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Does training affect the tactile oblique effect?

Does training affect the tactile oblique effect?


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In the visual sciences it is known that the oblique effect can be reduced by means of training. The oblique effect is observed when testing subjects psychophysically with a grating acuity task (e.g., the BaGa test). Visual acuity is better when horizontal or vertical gratings are tested than when diagonals are used. The performance in discerning diagonal gratings has been shown to improve after training subjects, although performance in the cardinal directions stays better than the oblique stimuli.

The oblique effect has been observed in the tactile sense too (the sense of touch). However, the amount of papers in the scientific literature is quite restricted in the tactile modality. I wasn't able to find evidence in the literature whether training can improve people's performance in tactile diagonal grating tasks.

Can training reduce the oblique effect in the tactile modality, comparable to that observed in visual grating tasks?


Indeed, research on this particular question is somewhat lacking, but what is available suggests that training does improve performance in tactile tests of the oblique effect.

In an article published 1999, Gentaz & Rossetti lament:

Unfortunately, the effect of practice on the haptic oblique effect has not been yet studied.

An indication that this might soon be remedied was noted in Junker-Tschopp, Gentaz & Viviani (2010):

We used bars instead of fuzzy stimuli (such as Gabor's patches) because this study is part of a larger project in which we also tested learning effects in the haptic modality (blindfolded participants explored manually a rod with varying orientations).

It does not look like the results of this "larger project" were ever published. However, they are reviewed in the book Psychology of Touch and Blindness by Morton A. Heller and Edouard Gentaz (one of the authors of the above mentioned papers) published in 2013 (pp 56-57):

… Junker-Tschopp, Gentaz, and Viviani (2010) investigated the extent to which visual and haptic perception are penetrable by cognitive factors by assessing the effect of learning on the perception of orientations. The "oblique effect" questions the nature of the linkages between perception and cognition… In the haptic modality, the results showed that practice resulted in a general dramatic improvement of orientation discriminabilty. Furthermore, the anisotropic bias in orientation perception is actually suppressed by a global learning paradigm…

These results are in line with the idea that the persistence of the oblique effect across modalities indicates that it is situated in higher cognitive processes (it is a top-down effect). This theory is backed by evidence demonstrating the similarity of the effect across visual and tactile modalities, so the effect of training would be expected to be similar in both.

Unfortunately, not everything is the same about the oblique effect across modalities, and authors note differences such as the role of gravity cues, memory constraints, reference frame, and while training does improve discrimination, it never eliminates the oblique effect, suggesting some bottom-up influence, and hence the potential for differences in results.

In a recent review, Mier (2014) examines the influence of training and feedback on the haptic perception of parallelity, and comes to a more guarded conclusion suggesting a more significant role for bottom-up processes:

… Kappers and coworkers (2008) found that the deviations were only marginally affected by training and feedback. Without informing their participants about their biased performance, they studied the effects of visual training (seeing the correct orientations), haptic training (feeling the correct orientations) and combined visuo-haptic training (seeing and feeling the correct orientations). In addition they studied the effect of error feedback on the performance of the participants, again under visual, haptic and visual-haptic conditions. They showed that the robustness of the deviations persisted even after participants received haptic and/or visual feedback and training. Haptic or visual training did not significantly decrease the magnitude of the deviations, only combining both training modes resulted in a small but significant improvement… Although providing participants with haptic and visual feedback about their errors reduced the deviations, performance was still far from being veridical… As the authors state, it might be that extension of the feedback phase would eventually lead to more veridical parallel matching.

Compared to the visual realm, where training has failed to eliminate the oblique effect, the effectiveness of training on the tactile oblique effect is unclear. The first study suggests that training is more effective on the tactile oblique effect, and is capable of entirely eliminating it, while the second study suggests that the tactile effect is less amenable to training than in the visual modality. Note however, that the second study refers specifically to haptic perception of parallelity, which is a specific sub-case of the oblique effect where exceptionally large oblique effects have been found, and therefore may not be applicable in general. More research is needed.


Studies reported in this paper have been supported by grants from the following foundations and granting agencies: the Lundbeck Foundation (to Ron Kupers), the European Union (Grant IST-2001-38040 and IST-2006-027141 to Pietro Pietrini), the Italian Ministry of Education, University and Research (PRIN RBNE018ET9-003, 200411841, and 2006117208 to Pietro Pietrini), Fondazione IRIS, Castagneto Carducci (Livorno, Italy to Pietro Pietrini), the Danish Medical Research Council (to Maurice Ptito), and the Harland Sanders Foundation (to Maurice Ptito). Pietro Pietrini and Emiliano Ricciardi wish to thank the Unione Italiana Ciechi for its support to the blindness research program, and the MRI Laboratory at the Fondazione “Gabriele Monasterio” Regione Toscana/CNR (Pisa, Italy).

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Keywords: vision, blindness, consciousness, qualia, cross-modal plasticity, supramodality, rewiring

Citation: Kupers R, Pietrini P, Ricciardi E and Ptito M (2011) The nature of consciousness in the visually deprived brain. Front. Psychology 2:19. doi: 10.3389/fpsyg.2011.00019

Received: 23 November 2010 Paper pending published: 04 January 2011
Accepted: 25 January 2011 Published online: 14 February 2011.

Morten Overgaard, Aarhus University, Denmark

Ryota Kanai, University College London, UK
Steven Laureys, University of Liège, Belgium

Copyright: © 2011 Kupers, Pietrini, Ricciardi and Ptito. This is an open-access article subject to an exclusive license agreement between the authors and Frontiers Media SA, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are credited.


Imagining angles and orientations

The foregoing supposes that limited visual imagery ability might hamper blind individuals in their processing of haptic space. More compelling evidence would of course follow from a direct test of imagery ability in the blind. In a review Kaski (2002) convincingly argued that even congenitally blind individuals can work with mental images. Still, there might be quantitative and qualitative performance differences with sighted persons which could effect certain aspects of haptic space processing (cf. Aleman et al. 2001 Cornoldi and Vecchi 2003). Thinus-Blanc and Gaunet (1997) suggested that lack of vision from early in life would lower the amount of information stored in the form of mental images and complicate executing complex computations that rely on such types of representations. Noordzij et al. (2007) conducted a study on imagery ability in blind and sighted which appears directly relevant for the current issue of haptic orientation processing. While on an auditory and visual form imagery task, there were only marginal differences between groups, sighted individuals outperformed the blind on a spatial imagery task. Importantly, this task asked participants to generate analogue images of two digitally presented clocks times and to compare the angles between the hands of the clocks for this pair of times.

As can been seen in Fig.  6 , while all groups showed an inverse linear relation between angular differences and error rates, indicating continuous, analogue mental computations, the blind groups clearly had more difficulty here. This suggests a difficulty in mental imaging of spatial orientations. 2 We wish to argue that this also affects the perception and interpretation of the orientations which the hands feel.

Judging the angles between the hands of the clock of digitally presented pairs of clock times. Adapted from Noordzij et al. (2007)


Multimodal spatial orientation deficits in left-sided visual neglect

Patients with right-sided temporo-parietal lesions often show contralesional neglect. However, neglect patients may also show spatial–perceptual deficits beyond the bisection and space exploration deficits frequently assessed in the horizontal plane, that is, deficits in the judgment of the subjective visual vertical or horizontal. In a recent study (Kerkhoff, G. & Zoelch, C., Disorders of visuo–spatial orientation in the frontal plane in patients with visual neglect following right or left parietal lesions. Exp. Brain Res., 1998122:108–120) we found significant perturbations in the perception of these three visual–spatial axes in patients with contralesional neglect from right or left parietal lesions. To examine if this finding extends also to another modality we investigated how neglect patients perform tasks of visual– and tactile–spatial judgments of axis-orientation in the frontal plane. Visual–spatial and tactile–spatial judgments of the subjective vertical, horizontal and a right oblique orientation were obtained from patients with and without neglect as well as from normal subjects. Patients with left neglect showed a significant, contraversive tilt of all three visual–spatial axes (+5.6° to +9.5°, counterclockwise), and of the three tactile–spatial axes as well (+5.2° to +10.5°, counterclockwise). In contrast, right and left hemisphere lesioned control patients without neglect and normal control subjects showed unimpaired visual and tactile–spatial judgments (constant errors: <1.0°). Difference thresholds in the visual–spatial tasks and unsigned errors in the tactile–spatial tasks were selectively elevated in the neglect group in contrast to all other subject groups. Spatial orientation deficits were significantly associated with the severity of clinical neglect (r=0.55–0.88), and with the patients’ ambulation performance (r=0.45–0.70). Furthermore, crossmodal axis orientation tests in two neglect patients showed a similar counterclockwise tilt of +5° to +15°, suggesting a similar spatial deficit in both modalities. Orientation judgments were significantly aggravated by a 25°-tilt of the head to the left, as tested in one neglect patient, while a comparable rightward head-tilt improved spatial judgments in both modalities. This suggests that spatial orientation judgments are significantly modulated by gravitational input in neglect patients. Together these results are interpreted as evidence for multisensory spatial orientation deficits in neglect patients which are modulated by head-position and are related to their accompanying postural impairment.


Cognitive Psychology Study Guide Questions and Ch. 1-4 Book Questions for EXAM 1

After the lesion, the rats were still able to run through the maze without issue.

Lashley concluded that over time, after learning, you have a mental version of something, such as the map of the maze somewhere in your brain.

When brain damage occurs, you have location and size of injury

location: you still have mostly intact memory,

b) Thesis: Descartes: Sense is not reliable, logic (rationalism) is the only thing that is reliable & the Evil Genius Theory.

Antithesis: (British Empericists) Lock/Berekley/Hume: Sense is the only thing that is reliable, for physical aspects are not reliable & tabala rasa (blank slate, when you are born) and EXPERIENCE ALLOWS US TO GAIN KNOWLEDGE

Synthesis: Kant: Categories of the understanding: Three buckets (organizational structure like Thesis), God, cause, etc. When you are born, buckets are empty (TABALA RASA), and as you experience things, these go into the buckets, which allow you to gain knowledge through experience.


Haptic perception: A tutorial

This tutorial focuses on the sense of touch within the context of a fully active human observer. It is intended for graduate students and researchers outside the discipline who seek an introduction to the rapidly evolving field of human haptics. The tutorial begins with a review of peripheral sensory receptors in skin, muscles, tendons, and joints. We then describe an extensive body of research on “what” and “where” channels, the former dealing with haptic perception of objects, surfaces, and their properties, and the latter with perception of spatial layout on the skin and in external space relative to the perceiver. We conclude with a brief discussion of other significant issues in the field, including vision-touch interactions, affective touch, neural plasticity, and applications.

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Notable Research [ edit | edit source ]

Roger Shepard and Metzler (1971) originally discovered this phenomenon. Their research showed that the reaction time for participants to decide if the pair of items matched or not was linearly proportional to the angle of rotation from the original position. That is, the more an object has been rotated from the original, the longer it takes an individual to determine if the 2 images are of the same object or enantiomorphs (Sternberg 247).

In further research, Shepard and Cooper (1982) have proposed the concept of a "Mental Imagery" facility, which is responsible for the ability to mentally rotate visual forms. Additionally, it has been found it does not matter on which axis an object is rotated, but rather the degree to which it is rotated that has the most significant effect on response time. So rotations within the depth plane (i.e., 2D rotations) and rotations in depth (3D rotations) behave similarly. Thus, the matching requires more time as the amount of depth rotation increases, just as for within the depth plane.

In subsequent research, it has been found that response times increase for degraded stimuli and can decrease when participants are allowed to practice mentally rotating imagery (Sternberg 247). This research has been instrumental in showing how people use mental representations to navigate their environments.

Recent breakthroughs have allowed psychologists to discover what parts of the brain correspond to the use of this mental imagery function. Using Functional Magnetic Resonance Imaging, psychologists have shown that when participants are performing mental rotation tasks, there is activation in Brodmann's areas 7A and 7B, the middle frontal gyrus, extra-striate cortex, the hand somastosensory cortex, and frontal cortex (Cohen et al.).


What is the theoretical basis for EMDR therapy?

Shapiro (1995) developed the Accelerated Information Processing model to describe and predict the effects of EMDR therapy. More recently, Shapiro (2001, 2018) expanded this into the Adaptive Information Processing (AIP) model to broaden its applicability. She hypothesizes that humans have an inherent information processing system that generally processes the multiple elements of experiences to an adaptive state where learning takes place. She conceptualizes memory as being stored in linked networks that are organized around the earliest related event and its associated affect. Memory networks are understood to contain related thoughts, images, emotions, and sensations. The AIP model hypothesizes that if the information related to a distressing or traumatic experience is not fully processed, the initial perceptions, emotions, and distorted thoughts will be stored as they were experienced at the time of the event. Shapiro argues that such unprocessed experiences become the basis of current dysfunctional reactions and are the cause of many mental disorders. She proposes that EMDR therapy successfully alleviates mental disorders by processing the components of the distressing memory. These effects are thought to occur when the targeted memory is linked with other more adaptive information. When this occurs, learning takes place, and the experience is stored with appropriate emotions able to guide the person in the future.


Discussion

The 2PD task is widely used clinically (Dellon, 1981 American Society for Surgery of the Hand, 1983 Van Boven and Johnson, 1994 Lundborg and Rosen, 2004 Jerosch-Herold, 2005 Campbell et al., 2013) and has been used also in several research laboratories to characterize tactile spatial acuity in healthy populations (Godde et al., 2000 Kennett et al., 2001 Dinse et al., 2006 Boles and Givens, 2011). Nevertheless, our results confirm that the 2PD threshold is not a pure measure of spatial acuity. The data support the use of an equally convenient alternative task – 2POD. Unlike 2PD, 2POD performance approaches chance levels as tip separation approaches zero, as expected of a rigorous measure of spatial acuity.

2PD Performance Benefits from a Non-Spatial Cue

Our findings support and extend upon a previous literature revealing that the 2PD task presents a non-spatial cue. Like Johnson and Phillips (1981), who conducted 2PD testing on the fingertip, we found that participants could reliably discriminate between a single point and two points at zero separation. On the fingertip, finger base, palm, and forearm, the mean 2PD γ value was significantly above 0.5, indicating that participants were able to perform correctly even at zero tip separation. Thus, 2PD performance is starkly inconsistent with the known spatial distribution of SA-1 mechanoreceptive afferents (Johansson and Vallbo, 1979, 1980 Olausson et al., 2000). We conclude that the 2PD task presents a non-spatial cue, allowing participants to infer the presence of two points without distinctly perceiving them.

We concur with Craig and Johnson (2000) that a likely non-spatial cue in the 2PD task is a response magnitude cue: due either to skin mechanics or to neural interactions among branches of individual afferent fibers, two closely spaced stimulus points elicit fewer action potentials in the underlying afferents than does a single-point of equal indentation (Vega-Bermudez and Johnson, 1999). For instance, when a one-point stimulus over an SA-1 receptive field center is compared to a two-point stimulus consisting of that same point plus another at 1 mm distance, the two-point stimulus elicits on average about 30% fewer action potentials. A similar effect, though weaker in magnitude, is observed when neither point overlies the center of the receptive field (Vega-Bermudez and Johnson, 1999). Thus, by merely detecting the total number of action potentials elicited in the afferent population rather than the spatial profile of neural activity, a participant could infer whether the stimulus contained one point or two (Figures 8A,B).

Figure 8. Neural response magnitude cues in the 2PD task. The three panels show hypothetical activity profiles of a population of central somatosensory neurons in response to three stimulus configurations: (A) a single point, (B) two closely spaced points, and (C) two points separated by a greater distance. We assume that the activity of central neurons reflects approximately that of the SA-1 afferents, described in Vega-Bermudez and Johnson (1999). In the textbook view of the 2PD task, the stimulus configurations illustrated in (A) and (B) would be indistinguishable from one another, because both configurations result in a single peak of neural activity. However, the neurophysiological data (Vega-Bermudez and Johnson, 1999) suggest that the population response in (B) is of lower magnitude than in (A), a cue that allows the participant to distinguish (A) from (B) by non-spatial means. In (C), the two activity peaks are indeed distinguishable spatially in addition, because each activity peak in (C) has equal height to the single peak in (A), the total population response in (C) is greater that in (A), giving rise to another magnitude cue.

We note that a magnitude cue will also exist, in the opposite direction, at somewhat larger tip separations, where interactions between stimuli are not expected at the single-neuron level. For instance, a two-point stimulus at 1 cm separation should elicit about twice the number of action potentials in the afferent population as would a one-point stimulus of equal indentation, because the two-point stimulus will activate about twice as many neurons (Figures 8A,C). Therefore, the 2PD task is apparently beset with magnitude cues at all tip separations.

An additional non-spatial cue that might sometimes accompany the 2PD task is a temporal cue: if the investigator fails to apply the two points simultaneously, the participant may perceive two contacts that are distinct in time. In this case, the participant could infer that two points touched the skin, even when unable to distinguish the points spatially. A limitation of any manual stimulus application method is that exact simultaneity is not achievable. Because humans are able to distinguish temporal delays between tactile stimuli of approximately 10 ms (Gescheider, 1967 Gescheider et al., 2003), any delay of this duration or longer between the two points of contact could produce a perceptible temporal cue. We note, however, that even when the 2PD task was conducted with an automated apparatus that touched the two tips against the skin with less than 2 ms delay, performance was approximately 80%-correct at zero tip separation (Johnson and Phillips, 1981). Thus, a temporal cue, while plausibly facilitating 2PD task performance under manual stimulus delivery, is unlikely to account for the extraordinary performance of participants at zero tip separation.

An alternate explanation for above-chance 2PD performance at zero tip separation, put forth by Stevens and Patterson (1995), is that participants make use of a length cue: two apposed points might feel longer than a single point. However, we believe it unlikely that our participants could detect the 0.25 mm difference in length between our single-point stimulus and the two apposed points. In a length discrimination experiment using raised edges of either 0.5 or 5 mm baseline length, Stevens and Patterson (1995) reported that on the fingertip the average adult participant could distinguish with 71% accuracy edges that differed by 0.8𠄰.9 mm in length. This length discrimination threshold is consistent with the estimated SA-1 receptive field spacing on the fingertip of approximately 1 mm (Johansson and Vallbo, 1979, 1980 Olausson et al., 2000). The implication of this finding is that the 2PD task would present a perceptual length cue at zero tip separation on the fingertip whenever the individual points have a size of approximately 0.8 mm or more. This would seem to rule out a length cue in the present study, as our point stimulus had a width of approximately 0.25 mm. Furthermore, to be detectable on the finger base, palm, and forearm, which have lower receptor densities than the fingertip, the length difference would presumably need to be much larger than 0.8 mm. Nevertheless, our participants performed significantly above chance at zero tip separation on those body sites as well.

2PD Performance Reflects Both Spatial and Non-Spatial Information

Because it is contaminated by one or more non-spatial cues, the 2PD task is prone to yield spuriously good performance. Consequently, tactile spatial deficits – particular if not severe – may be undetected or underestimated by 2PD testing. For instance, van Nes et al. (2008) reported that 2PD testing detected mild polyneuropathy caused by diabetes mellitus, chronic inflammatory demyelinating polyneuropathy, Guillain-Barré syndrome, uremia, and other causes, with a sensitivity of only 28%. Similarly, Van Boven and Johnson (1994) found that following elective mandibular surgery that injured but did not transect the inferior alveolar nerve, 2PD on the lip returned to normal levels much earlier in the course of recovery than did grating orientation performance, a rigorous measure of spatial acuity (see below). The authors argue that, owing to the presence of non-spatial cues, 2PD grossly overestimated the initial recovery of tactile spatial function.

Despite the presence of non-spatial cues, it would be an overly critical indictment to conclude that 2PD conveys no information regarding a patient’s spatial acuity. It seems clear that spatial as well as non-spatial cues influence 2PD task performance, particularly at larger tip separations. Presumably for this reason, more severe injuries, such as nerve transections, do result in lasting elevation of 2PD thresholds despite the return of tactile sensitivity as measured by monofilament testing (Rosen et al., 2000 Jerosch-Herold, 2003). Nerve transection, unlike nerve crush, is thought to result in the misdirection of sensory axons during re-innervation the shuffling of these axons causes severe deficits in spatial acuity (Van Boven and Johnson, 1994 Rosen et al., 2000), thereby elevating the 2PD threshold.

Among the neurologically healthy participants tested here, fewer than half had measurable 75%-correct 2PD thresholds on the four skin sites due presumably to non-spatial cues, performance did not consistently drop below 75%-correct even at zero tip separation. Nevertheless, the 2PD performance of all participants did fall below 95%-correct at small tip separations. Analyzing participants’ 95%-correct thresholds on the four body sites, we found that they correlated with mean receptive field spacing. This result is in keeping with previous reports that 2PD performance worsens on skin areas with sparser receptor distribution (Weinstein, 1968). Furthermore, the 95%-correct thresholds on the 2PD task did not differ significantly from those on the 2POD task. Presumably, at larger tip separations when distinct points are more reliably perceptible, participants do make use of the spatial pattern of the afferent population discharge.

For researchers who wish to use the 2IFC 2PD task, these results might suggest the adoption of the 95%-correct threshold as a valid performance measure. Nevertheless, we caution that the accurate estimation of a 95%-correct threshold is difficult. Conducting computer simulations of sensory tests using the method of limits, for instance, we found that the test-retest variance of the 95%-correct threshold estimate was consistently – and often considerably – greater than that of the 75%-correct threshold estimate. This difference owes to the shallower slopes of the psychometric functions (Figure 4) as they near the upper asymptote, which translates into a greater uncertainty in the x-axis value of the estimate, caused by any uncertainty in the %-correct measurement (Zuberbühler, 2002). Rather than attempting to estimate a 95%-correct threshold, we suggest that clinicians and researchers simply set aside the 2PD task and replace it with one that ensures a more purely spatial measure of acuity.

In this study, we conducted a 2IFC version of the 2PD task in order to most accurately assess the presence of non-spatial cues. In the 2IFC version, because a single-point and a two-point stimulus are presented on each trial, the participants are able to directly compare the neural responses that occur in the two configurations. Participants may therefore rather quickly become aware of non-spatial cues in this version of the task. A commonly used alternative version of the task employs single-interval trials. In each trial, the participant is stimulated just once, with either one or two-points, and asked to identify the configuration. This single-interval version of the task, though subject to the effects of response criteria (Gescheider, 1997 MacMillan and Creelman, 2005), may in fact be preferable to the 2IFC version, because with appropriate instruction the participant can be encouraged to respond “two” only when two distinct points are clearly perceived (Kalisch et al., 2007). The single-interval task may therefore mitigate the effect of neural magnitude cues on performance, thereby yielding a more purely spatial measure of acuity. In this regard, we note that the average single-interval 2PD 50% correct threshold obtained by Kalisch et al. (2007) from the right index fingers of untrained participants was approximately 1.6 mm, a tip separation that presented in our 2IFC 2PD task would yield on average 85% correct performance (see Figure 4A). Based on our finding that the 2PD and 2POD tasks yield similar performance at large tip separations, we suspect that the thresholds measured by Kalisch et al. (2007) indeed reflect primarily the participant’s spatial acuity. In general, the single-interval 2PD task, combined with instructions to participants to adopt an appropriately conservative response criterion, may produce the most reliable spatial acuity data achievable with the 2PD task.

2POD is a Rigorous and Convenient Measure of Tactile Spatial Acuity

Unlike the 2PD task, the 2POD task involves the spatial discrimination of orientation, with two points always presented. Thus, we reasoned that the 2POD task would avoid the non-spatial cues that plague the 2PD task: the neural population response magnitude should be the same, on average, for the two orientations, and a temporal delay between the two points of contact, if present, would not compromise the task to perform successfully, the participant would still need to discern the orientation of the points. Therefore, we predicted that 2POD performance would approach chance as the tip separation approached zero. Our results confirmed this prediction.

To our knowledge, we are the first to propose the exact version of the 2POD task described here, though Stevens and colleagues used similar tasks (Stevens and Patterson, 1995 Stevens et al., 1996) and Weber himself explored two-point perception in the horizontal compared to the vertical orientation (Weber, 1996). In Stevens and Patterson (1995), a pair of longitudinal two-point stimuli and a pair of two-point stimuli of non-matching orientations (longitudinal and transverse) were presented on every trial the participant was asked to identify which interval had the non-matching pairs. In Stevens et al. (1996), a single two-point stimulus was given in either longitudinal or transverse orientation, and the participant was asked to identify the orientation. Some participants in Stevens and Patterson (1995) performed correctly at zero tip separation, perhaps because relatively large caliper tips (0.44 mm each) permitted the perception of orientation even when fully closed. To prevent this, we recommend that the 2POD task be performed with caliper tips of approximately 0.25 mm diameter.

The 2POD task that we have used combines the rigor of a gold standard in tactile spatial acuity testing, the grating orientation task, with the convenience of the 2PD task. In the grating orientation task, participants attempt to discern the orientation (typically, horizontal or vertical) of square-wave gratings with equal ridge and groove width. Groove width is reduced to make the task more difficult, or increased to make it easier. Acuity is measured as the groove width whose orientation the participant can discern with a particular probability (e.g., 75%-correct). Whether a grating is applied horizontally or vertically, it is expected to elicit on average the same afferent population discharge magnitude only the spatial structure of the population discharge varies. Therefore, to perform the task correctly the participant must discern the spatial pattern of afferent activity, rendering this a rigorous test of tactile spatial acuity (Johnson and Phillips, 1981 Gibson and Craig, 2002, 2006). The similarity to the 2POD task is clear.

While tactile research laboratories such as ours make extensive use of the grating orientation task (Goldreich and Kanics, 2003 Goldreich et al., 2009 Peters et al., 2009 Wong et al., 2011a,b, 2013), we recognize that the task has certain practical disadvantages, particularly as concerns the clinical setting. Among these is that each grating must be prefabricated consequently, the variable of interest, groove width, cannot be adjusted outside a pre-determined range. This is particularly problematic if one wishes to test patients who may have atypical spatial acuity due to neurological damage. The 2POD task does not suffer from this practical inconvenience. Rather, like the 2PD task, the 2POD task is remarkably flexible in requiring only a single tool (calipers) that is easily adjustable during testing.

Recommendations for Future Studies and for Clinical Practice

In conclusion, our data confirm that the 2IFC 2PD task is contaminated by one or more unintended non-spatial cues that result in inflated spatial acuity reports. An alternative task, 2POD, provides a rigorous measure of spatial acuity. The advantage of 2POD over 2PD as a measure of spatial acuity is summarized in Figure 9.

Figure 9. Advantage of 2POD over 2PD for tactile spatial acuity assessment. Each panel depicts idealized circular receptive fields of nine SA-1 afferents for clarity, only non-overlapping fields are shown. Asterisks represent point stimuli. In 2PD, the participant attempts to distinguish between a single point (A) and two points separated by some distance, e.g., (B) or (C). For illustration, we assume that a single point evokes 100 action potentials per second in the central SA-1. When two points fall within the same receptive field (B), they evoke fewer action potentials than the single point. For instance, two points at 1 mm separation evoke on average 88% the firing rate of a single point (Vega-Bermudez and Johnson, 1999). Thus, the participant can distinguish one from two points based on the number of action potentials (magnitude cue), even when the two points cannot be individually perceived. When separated by a greater distance (C), the two points can be perceived, because they fall within separate receptive fields (spatial cue). In addition, the magnitude cue has reversed direction, as the total number of action potentials in the two-point condition (200) is twice that in the one-point condition. Thus, the two-point task conveys spatial information at larger separations but is contaminated by a magnitude cue at all separations. In 2POD, the participant attempts to distinguish between two points separated horizontally and two points separated vertically by the same distance: (B) vs. (D), or (C) vs. (E). These stimuli evoke an equal number of action potentials, eliminating the magnitude cue and forcing the participant to rely on purely spatial information. When the points fall within a single receptive field, as in (B) and (D), their orientation is indistinguishable. When the points fall within distinct receptive fields, as in (C) and (E), their orientation is distinguishable.

We have performed the 2POD task using vertically and horizontally (i.e., longitudinally and transversely) oriented stimuli. One recommendation for future studies and for clinical practice would be to use oblique (e.g., 녅-degree) orientations. The use of oblique stimuli would offer two practical advantages. First, it would permit greater tip separations. On the digits and limbs, the maximum tip separation in the vertical-horizontal 2POD task is limited to the width of the body part, a constraint that is overcome by the use of oblique stimuli. Second, the use of oblique stimuli would prevent magnitude cues that might arise from receptive field anisotropy. A majority of receptive fields on the fingers and palm reportedly are elongated rather than circular furthermore, roughly two-thirds of the elongated fields are oriented longitudinally with respect to the arm (Johansson and Vallbo, 1980). Perhaps for this reason, performance anisotropy has been reported on several body areas, in a variety of tactile acuity tests (Essock et al., 1992 Stevens and Patterson, 1995 Gibson and Craig, 2005), beginning with the report by Weber himself that 2PD acuity was better when the tips were aligned transversely (Weber, 1996). The use of oblique stimuli should prevent performance anisotropy caused by alignment of the two-point configuration in parallel or orthogonal to the average receptive field orientation.

Given its evident advantages, we recommend that 2POD replace 2PD testing in the clinic and in research settings. Additional studies should be carried out to further validate the 2POD task by measuring inter-rater and test-retest reliability and by comparing 2POD with grating orientation thresholds in neurologically healthy participants and in patients. Our laboratory has previously shown that grating orientation thresholds correlate with fingertip surface area (Peters et al., 2009), suggesting that receptive fields are more widely spaced in larger fingers. As an exploratory analysis, we checked for this effect in the current 2PD and 2POD data, but not surprisingly, we observed no significant correlations between finger size and performance on either task in our relatively small participant sample. In analogy with previous grating orientation studies, we predict that, with sufficiently large sample sizes (Peters et al., 2009) or with trained participants (Wong et al., 2013), 2POD performance will also be found to correlate with finger size.

Although we have used adaptive psychophysical data collection methods and mathematical analyses in order to evaluate the 2POD and 2PD tasks, we suggest that more practical, less elaborate procedures be used in the clinic. To facilitate the use of the task for clinical purposes, we recommend that the patient be stimulated with 10 or 20 2POD 2IFC trials at each of several tip separations. A plot could then be made of the number of correct responses at each separation. The interpolated tip separation corresponding to 75%-correct could be reported as the patient’s spatial acuity. Alternatively, for greater convenience and to reduce testing time, a single-interval 2POD task could be used, in which the participant is stimulated just once on each trial, and attempts to identify the stimulus orientation we favor the 2IFC testing protocol, however, to prevent possible criterion effects (Gescheider, 1997). For equipment, we recommend the use of adjustable calipers with pointed tips not exceeding 0.25 mm width and 0.5 mm thickness. One such device is the Absolute Digimatic caliper (Mitutoyo Corp.) used in this study many similar devices are available from Starrett Co., Digital Measurement Metrology, Inc., and other companies. The cost of these calipers ranges from under ␠ to over 𤄀, depending on their material and precision.


Abstract

Spatial deficits are frequent after brain damage, particularly right hemisphere stroke. Visual judgments of line orientation (LINE) are often impaired after right parietal lesions. Perception of line orientation is an important visuoperceptual component of visuoconstructive capacities. Yet, little is known about modulating factors in LINE and effective treatments are rare for this disorder. Studies in patients with spatial neglect show that horizontal random dot motion (RDM) significantly modulates horizontal spatial disorders, both transiently and permanently after treatment. In the current study, we investigated whether rotational RDM modulates judgements in an oblique LINE task in 20 patients with right-hemispheric first ever stroke (10 of them with a disorder in LINE and 10 without such a disorder), and 10 healthy, age-matched subjects. Subjects were tested under three experimental conditions: (1) with a static background of small white dots, (2) with slow clockwise or (3) counterclockwise circular RDM of these background stimuli, while they performed the LINE task. In the baseline condition with static background, the impaired patient group showed a significant counterclockwise tilt. Clockwise rotating RDM normalized this deficit transiently but completely, while counterclockwise rotating RDM slightly aggravated it, though not significantly. Tilts in the LINE task were significantly correlated with left visuospatial neglect. Similar but much smaller effects were obtained in the spatially unimpaired patients and the normal controls. These results show that rotational RDM modulates deficits of line orientation in patients with right-sided stroke, possibly by influencing higher spatial representations devoted to the perception of oblique lines.


Abstract

Spatial deficits are frequent after brain damage, particularly right hemisphere stroke. Visual judgments of line orientation (LINE) are often impaired after right parietal lesions. Perception of line orientation is an important visuoperceptual component of visuoconstructive capacities. Yet, little is known about modulating factors in LINE and effective treatments are rare for this disorder. Studies in patients with spatial neglect show that horizontal random dot motion (RDM) significantly modulates horizontal spatial disorders, both transiently and permanently after treatment. In the current study, we investigated whether rotational RDM modulates judgements in an oblique LINE task in 20 patients with right-hemispheric first ever stroke (10 of them with a disorder in LINE and 10 without such a disorder), and 10 healthy, age-matched subjects. Subjects were tested under three experimental conditions: (1) with a static background of small white dots, (2) with slow clockwise or (3) counterclockwise circular RDM of these background stimuli, while they performed the LINE task. In the baseline condition with static background, the impaired patient group showed a significant counterclockwise tilt. Clockwise rotating RDM normalized this deficit transiently but completely, while counterclockwise rotating RDM slightly aggravated it, though not significantly. Tilts in the LINE task were significantly correlated with left visuospatial neglect. Similar but much smaller effects were obtained in the spatially unimpaired patients and the normal controls. These results show that rotational RDM modulates deficits of line orientation in patients with right-sided stroke, possibly by influencing higher spatial representations devoted to the perception of oblique lines.


Discussion

The 2PD task is widely used clinically (Dellon, 1981 American Society for Surgery of the Hand, 1983 Van Boven and Johnson, 1994 Lundborg and Rosen, 2004 Jerosch-Herold, 2005 Campbell et al., 2013) and has been used also in several research laboratories to characterize tactile spatial acuity in healthy populations (Godde et al., 2000 Kennett et al., 2001 Dinse et al., 2006 Boles and Givens, 2011). Nevertheless, our results confirm that the 2PD threshold is not a pure measure of spatial acuity. The data support the use of an equally convenient alternative task – 2POD. Unlike 2PD, 2POD performance approaches chance levels as tip separation approaches zero, as expected of a rigorous measure of spatial acuity.

2PD Performance Benefits from a Non-Spatial Cue

Our findings support and extend upon a previous literature revealing that the 2PD task presents a non-spatial cue. Like Johnson and Phillips (1981), who conducted 2PD testing on the fingertip, we found that participants could reliably discriminate between a single point and two points at zero separation. On the fingertip, finger base, palm, and forearm, the mean 2PD γ value was significantly above 0.5, indicating that participants were able to perform correctly even at zero tip separation. Thus, 2PD performance is starkly inconsistent with the known spatial distribution of SA-1 mechanoreceptive afferents (Johansson and Vallbo, 1979, 1980 Olausson et al., 2000). We conclude that the 2PD task presents a non-spatial cue, allowing participants to infer the presence of two points without distinctly perceiving them.

We concur with Craig and Johnson (2000) that a likely non-spatial cue in the 2PD task is a response magnitude cue: due either to skin mechanics or to neural interactions among branches of individual afferent fibers, two closely spaced stimulus points elicit fewer action potentials in the underlying afferents than does a single-point of equal indentation (Vega-Bermudez and Johnson, 1999). For instance, when a one-point stimulus over an SA-1 receptive field center is compared to a two-point stimulus consisting of that same point plus another at 1 mm distance, the two-point stimulus elicits on average about 30% fewer action potentials. A similar effect, though weaker in magnitude, is observed when neither point overlies the center of the receptive field (Vega-Bermudez and Johnson, 1999). Thus, by merely detecting the total number of action potentials elicited in the afferent population rather than the spatial profile of neural activity, a participant could infer whether the stimulus contained one point or two (Figures 8A,B).

Figure 8. Neural response magnitude cues in the 2PD task. The three panels show hypothetical activity profiles of a population of central somatosensory neurons in response to three stimulus configurations: (A) a single point, (B) two closely spaced points, and (C) two points separated by a greater distance. We assume that the activity of central neurons reflects approximately that of the SA-1 afferents, described in Vega-Bermudez and Johnson (1999). In the textbook view of the 2PD task, the stimulus configurations illustrated in (A) and (B) would be indistinguishable from one another, because both configurations result in a single peak of neural activity. However, the neurophysiological data (Vega-Bermudez and Johnson, 1999) suggest that the population response in (B) is of lower magnitude than in (A), a cue that allows the participant to distinguish (A) from (B) by non-spatial means. In (C), the two activity peaks are indeed distinguishable spatially in addition, because each activity peak in (C) has equal height to the single peak in (A), the total population response in (C) is greater that in (A), giving rise to another magnitude cue.

We note that a magnitude cue will also exist, in the opposite direction, at somewhat larger tip separations, where interactions between stimuli are not expected at the single-neuron level. For instance, a two-point stimulus at 1 cm separation should elicit about twice the number of action potentials in the afferent population as would a one-point stimulus of equal indentation, because the two-point stimulus will activate about twice as many neurons (Figures 8A,C). Therefore, the 2PD task is apparently beset with magnitude cues at all tip separations.

An additional non-spatial cue that might sometimes accompany the 2PD task is a temporal cue: if the investigator fails to apply the two points simultaneously, the participant may perceive two contacts that are distinct in time. In this case, the participant could infer that two points touched the skin, even when unable to distinguish the points spatially. A limitation of any manual stimulus application method is that exact simultaneity is not achievable. Because humans are able to distinguish temporal delays between tactile stimuli of approximately 10 ms (Gescheider, 1967 Gescheider et al., 2003), any delay of this duration or longer between the two points of contact could produce a perceptible temporal cue. We note, however, that even when the 2PD task was conducted with an automated apparatus that touched the two tips against the skin with less than 2 ms delay, performance was approximately 80%-correct at zero tip separation (Johnson and Phillips, 1981). Thus, a temporal cue, while plausibly facilitating 2PD task performance under manual stimulus delivery, is unlikely to account for the extraordinary performance of participants at zero tip separation.

An alternate explanation for above-chance 2PD performance at zero tip separation, put forth by Stevens and Patterson (1995), is that participants make use of a length cue: two apposed points might feel longer than a single point. However, we believe it unlikely that our participants could detect the 0.25 mm difference in length between our single-point stimulus and the two apposed points. In a length discrimination experiment using raised edges of either 0.5 or 5 mm baseline length, Stevens and Patterson (1995) reported that on the fingertip the average adult participant could distinguish with 71% accuracy edges that differed by 0.8𠄰.9 mm in length. This length discrimination threshold is consistent with the estimated SA-1 receptive field spacing on the fingertip of approximately 1 mm (Johansson and Vallbo, 1979, 1980 Olausson et al., 2000). The implication of this finding is that the 2PD task would present a perceptual length cue at zero tip separation on the fingertip whenever the individual points have a size of approximately 0.8 mm or more. This would seem to rule out a length cue in the present study, as our point stimulus had a width of approximately 0.25 mm. Furthermore, to be detectable on the finger base, palm, and forearm, which have lower receptor densities than the fingertip, the length difference would presumably need to be much larger than 0.8 mm. Nevertheless, our participants performed significantly above chance at zero tip separation on those body sites as well.

2PD Performance Reflects Both Spatial and Non-Spatial Information

Because it is contaminated by one or more non-spatial cues, the 2PD task is prone to yield spuriously good performance. Consequently, tactile spatial deficits – particular if not severe – may be undetected or underestimated by 2PD testing. For instance, van Nes et al. (2008) reported that 2PD testing detected mild polyneuropathy caused by diabetes mellitus, chronic inflammatory demyelinating polyneuropathy, Guillain-Barré syndrome, uremia, and other causes, with a sensitivity of only 28%. Similarly, Van Boven and Johnson (1994) found that following elective mandibular surgery that injured but did not transect the inferior alveolar nerve, 2PD on the lip returned to normal levels much earlier in the course of recovery than did grating orientation performance, a rigorous measure of spatial acuity (see below). The authors argue that, owing to the presence of non-spatial cues, 2PD grossly overestimated the initial recovery of tactile spatial function.

Despite the presence of non-spatial cues, it would be an overly critical indictment to conclude that 2PD conveys no information regarding a patient’s spatial acuity. It seems clear that spatial as well as non-spatial cues influence 2PD task performance, particularly at larger tip separations. Presumably for this reason, more severe injuries, such as nerve transections, do result in lasting elevation of 2PD thresholds despite the return of tactile sensitivity as measured by monofilament testing (Rosen et al., 2000 Jerosch-Herold, 2003). Nerve transection, unlike nerve crush, is thought to result in the misdirection of sensory axons during re-innervation the shuffling of these axons causes severe deficits in spatial acuity (Van Boven and Johnson, 1994 Rosen et al., 2000), thereby elevating the 2PD threshold.

Among the neurologically healthy participants tested here, fewer than half had measurable 75%-correct 2PD thresholds on the four skin sites due presumably to non-spatial cues, performance did not consistently drop below 75%-correct even at zero tip separation. Nevertheless, the 2PD performance of all participants did fall below 95%-correct at small tip separations. Analyzing participants’ 95%-correct thresholds on the four body sites, we found that they correlated with mean receptive field spacing. This result is in keeping with previous reports that 2PD performance worsens on skin areas with sparser receptor distribution (Weinstein, 1968). Furthermore, the 95%-correct thresholds on the 2PD task did not differ significantly from those on the 2POD task. Presumably, at larger tip separations when distinct points are more reliably perceptible, participants do make use of the spatial pattern of the afferent population discharge.

For researchers who wish to use the 2IFC 2PD task, these results might suggest the adoption of the 95%-correct threshold as a valid performance measure. Nevertheless, we caution that the accurate estimation of a 95%-correct threshold is difficult. Conducting computer simulations of sensory tests using the method of limits, for instance, we found that the test-retest variance of the 95%-correct threshold estimate was consistently – and often considerably – greater than that of the 75%-correct threshold estimate. This difference owes to the shallower slopes of the psychometric functions (Figure 4) as they near the upper asymptote, which translates into a greater uncertainty in the x-axis value of the estimate, caused by any uncertainty in the %-correct measurement (Zuberbühler, 2002). Rather than attempting to estimate a 95%-correct threshold, we suggest that clinicians and researchers simply set aside the 2PD task and replace it with one that ensures a more purely spatial measure of acuity.

In this study, we conducted a 2IFC version of the 2PD task in order to most accurately assess the presence of non-spatial cues. In the 2IFC version, because a single-point and a two-point stimulus are presented on each trial, the participants are able to directly compare the neural responses that occur in the two configurations. Participants may therefore rather quickly become aware of non-spatial cues in this version of the task. A commonly used alternative version of the task employs single-interval trials. In each trial, the participant is stimulated just once, with either one or two-points, and asked to identify the configuration. This single-interval version of the task, though subject to the effects of response criteria (Gescheider, 1997 MacMillan and Creelman, 2005), may in fact be preferable to the 2IFC version, because with appropriate instruction the participant can be encouraged to respond “two” only when two distinct points are clearly perceived (Kalisch et al., 2007). The single-interval task may therefore mitigate the effect of neural magnitude cues on performance, thereby yielding a more purely spatial measure of acuity. In this regard, we note that the average single-interval 2PD 50% correct threshold obtained by Kalisch et al. (2007) from the right index fingers of untrained participants was approximately 1.6 mm, a tip separation that presented in our 2IFC 2PD task would yield on average 85% correct performance (see Figure 4A). Based on our finding that the 2PD and 2POD tasks yield similar performance at large tip separations, we suspect that the thresholds measured by Kalisch et al. (2007) indeed reflect primarily the participant’s spatial acuity. In general, the single-interval 2PD task, combined with instructions to participants to adopt an appropriately conservative response criterion, may produce the most reliable spatial acuity data achievable with the 2PD task.

2POD is a Rigorous and Convenient Measure of Tactile Spatial Acuity

Unlike the 2PD task, the 2POD task involves the spatial discrimination of orientation, with two points always presented. Thus, we reasoned that the 2POD task would avoid the non-spatial cues that plague the 2PD task: the neural population response magnitude should be the same, on average, for the two orientations, and a temporal delay between the two points of contact, if present, would not compromise the task to perform successfully, the participant would still need to discern the orientation of the points. Therefore, we predicted that 2POD performance would approach chance as the tip separation approached zero. Our results confirmed this prediction.

To our knowledge, we are the first to propose the exact version of the 2POD task described here, though Stevens and colleagues used similar tasks (Stevens and Patterson, 1995 Stevens et al., 1996) and Weber himself explored two-point perception in the horizontal compared to the vertical orientation (Weber, 1996). In Stevens and Patterson (1995), a pair of longitudinal two-point stimuli and a pair of two-point stimuli of non-matching orientations (longitudinal and transverse) were presented on every trial the participant was asked to identify which interval had the non-matching pairs. In Stevens et al. (1996), a single two-point stimulus was given in either longitudinal or transverse orientation, and the participant was asked to identify the orientation. Some participants in Stevens and Patterson (1995) performed correctly at zero tip separation, perhaps because relatively large caliper tips (0.44 mm each) permitted the perception of orientation even when fully closed. To prevent this, we recommend that the 2POD task be performed with caliper tips of approximately 0.25 mm diameter.

The 2POD task that we have used combines the rigor of a gold standard in tactile spatial acuity testing, the grating orientation task, with the convenience of the 2PD task. In the grating orientation task, participants attempt to discern the orientation (typically, horizontal or vertical) of square-wave gratings with equal ridge and groove width. Groove width is reduced to make the task more difficult, or increased to make it easier. Acuity is measured as the groove width whose orientation the participant can discern with a particular probability (e.g., 75%-correct). Whether a grating is applied horizontally or vertically, it is expected to elicit on average the same afferent population discharge magnitude only the spatial structure of the population discharge varies. Therefore, to perform the task correctly the participant must discern the spatial pattern of afferent activity, rendering this a rigorous test of tactile spatial acuity (Johnson and Phillips, 1981 Gibson and Craig, 2002, 2006). The similarity to the 2POD task is clear.

While tactile research laboratories such as ours make extensive use of the grating orientation task (Goldreich and Kanics, 2003 Goldreich et al., 2009 Peters et al., 2009 Wong et al., 2011a,b, 2013), we recognize that the task has certain practical disadvantages, particularly as concerns the clinical setting. Among these is that each grating must be prefabricated consequently, the variable of interest, groove width, cannot be adjusted outside a pre-determined range. This is particularly problematic if one wishes to test patients who may have atypical spatial acuity due to neurological damage. The 2POD task does not suffer from this practical inconvenience. Rather, like the 2PD task, the 2POD task is remarkably flexible in requiring only a single tool (calipers) that is easily adjustable during testing.

Recommendations for Future Studies and for Clinical Practice

In conclusion, our data confirm that the 2IFC 2PD task is contaminated by one or more unintended non-spatial cues that result in inflated spatial acuity reports. An alternative task, 2POD, provides a rigorous measure of spatial acuity. The advantage of 2POD over 2PD as a measure of spatial acuity is summarized in Figure 9.

Figure 9. Advantage of 2POD over 2PD for tactile spatial acuity assessment. Each panel depicts idealized circular receptive fields of nine SA-1 afferents for clarity, only non-overlapping fields are shown. Asterisks represent point stimuli. In 2PD, the participant attempts to distinguish between a single point (A) and two points separated by some distance, e.g., (B) or (C). For illustration, we assume that a single point evokes 100 action potentials per second in the central SA-1. When two points fall within the same receptive field (B), they evoke fewer action potentials than the single point. For instance, two points at 1 mm separation evoke on average 88% the firing rate of a single point (Vega-Bermudez and Johnson, 1999). Thus, the participant can distinguish one from two points based on the number of action potentials (magnitude cue), even when the two points cannot be individually perceived. When separated by a greater distance (C), the two points can be perceived, because they fall within separate receptive fields (spatial cue). In addition, the magnitude cue has reversed direction, as the total number of action potentials in the two-point condition (200) is twice that in the one-point condition. Thus, the two-point task conveys spatial information at larger separations but is contaminated by a magnitude cue at all separations. In 2POD, the participant attempts to distinguish between two points separated horizontally and two points separated vertically by the same distance: (B) vs. (D), or (C) vs. (E). These stimuli evoke an equal number of action potentials, eliminating the magnitude cue and forcing the participant to rely on purely spatial information. When the points fall within a single receptive field, as in (B) and (D), their orientation is indistinguishable. When the points fall within distinct receptive fields, as in (C) and (E), their orientation is distinguishable.

We have performed the 2POD task using vertically and horizontally (i.e., longitudinally and transversely) oriented stimuli. One recommendation for future studies and for clinical practice would be to use oblique (e.g., 녅-degree) orientations. The use of oblique stimuli would offer two practical advantages. First, it would permit greater tip separations. On the digits and limbs, the maximum tip separation in the vertical-horizontal 2POD task is limited to the width of the body part, a constraint that is overcome by the use of oblique stimuli. Second, the use of oblique stimuli would prevent magnitude cues that might arise from receptive field anisotropy. A majority of receptive fields on the fingers and palm reportedly are elongated rather than circular furthermore, roughly two-thirds of the elongated fields are oriented longitudinally with respect to the arm (Johansson and Vallbo, 1980). Perhaps for this reason, performance anisotropy has been reported on several body areas, in a variety of tactile acuity tests (Essock et al., 1992 Stevens and Patterson, 1995 Gibson and Craig, 2005), beginning with the report by Weber himself that 2PD acuity was better when the tips were aligned transversely (Weber, 1996). The use of oblique stimuli should prevent performance anisotropy caused by alignment of the two-point configuration in parallel or orthogonal to the average receptive field orientation.

Given its evident advantages, we recommend that 2POD replace 2PD testing in the clinic and in research settings. Additional studies should be carried out to further validate the 2POD task by measuring inter-rater and test-retest reliability and by comparing 2POD with grating orientation thresholds in neurologically healthy participants and in patients. Our laboratory has previously shown that grating orientation thresholds correlate with fingertip surface area (Peters et al., 2009), suggesting that receptive fields are more widely spaced in larger fingers. As an exploratory analysis, we checked for this effect in the current 2PD and 2POD data, but not surprisingly, we observed no significant correlations between finger size and performance on either task in our relatively small participant sample. In analogy with previous grating orientation studies, we predict that, with sufficiently large sample sizes (Peters et al., 2009) or with trained participants (Wong et al., 2013), 2POD performance will also be found to correlate with finger size.

Although we have used adaptive psychophysical data collection methods and mathematical analyses in order to evaluate the 2POD and 2PD tasks, we suggest that more practical, less elaborate procedures be used in the clinic. To facilitate the use of the task for clinical purposes, we recommend that the patient be stimulated with 10 or 20 2POD 2IFC trials at each of several tip separations. A plot could then be made of the number of correct responses at each separation. The interpolated tip separation corresponding to 75%-correct could be reported as the patient’s spatial acuity. Alternatively, for greater convenience and to reduce testing time, a single-interval 2POD task could be used, in which the participant is stimulated just once on each trial, and attempts to identify the stimulus orientation we favor the 2IFC testing protocol, however, to prevent possible criterion effects (Gescheider, 1997). For equipment, we recommend the use of adjustable calipers with pointed tips not exceeding 0.25 mm width and 0.5 mm thickness. One such device is the Absolute Digimatic caliper (Mitutoyo Corp.) used in this study many similar devices are available from Starrett Co., Digital Measurement Metrology, Inc., and other companies. The cost of these calipers ranges from under ␠ to over 𤄀, depending on their material and precision.


Cognitive Psychology Study Guide Questions and Ch. 1-4 Book Questions for EXAM 1

After the lesion, the rats were still able to run through the maze without issue.

Lashley concluded that over time, after learning, you have a mental version of something, such as the map of the maze somewhere in your brain.

When brain damage occurs, you have location and size of injury

location: you still have mostly intact memory,

b) Thesis: Descartes: Sense is not reliable, logic (rationalism) is the only thing that is reliable & the Evil Genius Theory.

Antithesis: (British Empericists) Lock/Berekley/Hume: Sense is the only thing that is reliable, for physical aspects are not reliable & tabala rasa (blank slate, when you are born) and EXPERIENCE ALLOWS US TO GAIN KNOWLEDGE

Synthesis: Kant: Categories of the understanding: Three buckets (organizational structure like Thesis), God, cause, etc. When you are born, buckets are empty (TABALA RASA), and as you experience things, these go into the buckets, which allow you to gain knowledge through experience.


Imagining angles and orientations

The foregoing supposes that limited visual imagery ability might hamper blind individuals in their processing of haptic space. More compelling evidence would of course follow from a direct test of imagery ability in the blind. In a review Kaski (2002) convincingly argued that even congenitally blind individuals can work with mental images. Still, there might be quantitative and qualitative performance differences with sighted persons which could effect certain aspects of haptic space processing (cf. Aleman et al. 2001 Cornoldi and Vecchi 2003). Thinus-Blanc and Gaunet (1997) suggested that lack of vision from early in life would lower the amount of information stored in the form of mental images and complicate executing complex computations that rely on such types of representations. Noordzij et al. (2007) conducted a study on imagery ability in blind and sighted which appears directly relevant for the current issue of haptic orientation processing. While on an auditory and visual form imagery task, there were only marginal differences between groups, sighted individuals outperformed the blind on a spatial imagery task. Importantly, this task asked participants to generate analogue images of two digitally presented clocks times and to compare the angles between the hands of the clocks for this pair of times.

As can been seen in Fig.  6 , while all groups showed an inverse linear relation between angular differences and error rates, indicating continuous, analogue mental computations, the blind groups clearly had more difficulty here. This suggests a difficulty in mental imaging of spatial orientations. 2 We wish to argue that this also affects the perception and interpretation of the orientations which the hands feel.

Judging the angles between the hands of the clock of digitally presented pairs of clock times. Adapted from Noordzij et al. (2007)


Multimodal spatial orientation deficits in left-sided visual neglect

Patients with right-sided temporo-parietal lesions often show contralesional neglect. However, neglect patients may also show spatial–perceptual deficits beyond the bisection and space exploration deficits frequently assessed in the horizontal plane, that is, deficits in the judgment of the subjective visual vertical or horizontal. In a recent study (Kerkhoff, G. & Zoelch, C., Disorders of visuo–spatial orientation in the frontal plane in patients with visual neglect following right or left parietal lesions. Exp. Brain Res., 1998122:108–120) we found significant perturbations in the perception of these three visual–spatial axes in patients with contralesional neglect from right or left parietal lesions. To examine if this finding extends also to another modality we investigated how neglect patients perform tasks of visual– and tactile–spatial judgments of axis-orientation in the frontal plane. Visual–spatial and tactile–spatial judgments of the subjective vertical, horizontal and a right oblique orientation were obtained from patients with and without neglect as well as from normal subjects. Patients with left neglect showed a significant, contraversive tilt of all three visual–spatial axes (+5.6° to +9.5°, counterclockwise), and of the three tactile–spatial axes as well (+5.2° to +10.5°, counterclockwise). In contrast, right and left hemisphere lesioned control patients without neglect and normal control subjects showed unimpaired visual and tactile–spatial judgments (constant errors: <1.0°). Difference thresholds in the visual–spatial tasks and unsigned errors in the tactile–spatial tasks were selectively elevated in the neglect group in contrast to all other subject groups. Spatial orientation deficits were significantly associated with the severity of clinical neglect (r=0.55–0.88), and with the patients’ ambulation performance (r=0.45–0.70). Furthermore, crossmodal axis orientation tests in two neglect patients showed a similar counterclockwise tilt of +5° to +15°, suggesting a similar spatial deficit in both modalities. Orientation judgments were significantly aggravated by a 25°-tilt of the head to the left, as tested in one neglect patient, while a comparable rightward head-tilt improved spatial judgments in both modalities. This suggests that spatial orientation judgments are significantly modulated by gravitational input in neglect patients. Together these results are interpreted as evidence for multisensory spatial orientation deficits in neglect patients which are modulated by head-position and are related to their accompanying postural impairment.


Notable Research [ edit | edit source ]

Roger Shepard and Metzler (1971) originally discovered this phenomenon. Their research showed that the reaction time for participants to decide if the pair of items matched or not was linearly proportional to the angle of rotation from the original position. That is, the more an object has been rotated from the original, the longer it takes an individual to determine if the 2 images are of the same object or enantiomorphs (Sternberg 247).

In further research, Shepard and Cooper (1982) have proposed the concept of a "Mental Imagery" facility, which is responsible for the ability to mentally rotate visual forms. Additionally, it has been found it does not matter on which axis an object is rotated, but rather the degree to which it is rotated that has the most significant effect on response time. So rotations within the depth plane (i.e., 2D rotations) and rotations in depth (3D rotations) behave similarly. Thus, the matching requires more time as the amount of depth rotation increases, just as for within the depth plane.

In subsequent research, it has been found that response times increase for degraded stimuli and can decrease when participants are allowed to practice mentally rotating imagery (Sternberg 247). This research has been instrumental in showing how people use mental representations to navigate their environments.

Recent breakthroughs have allowed psychologists to discover what parts of the brain correspond to the use of this mental imagery function. Using Functional Magnetic Resonance Imaging, psychologists have shown that when participants are performing mental rotation tasks, there is activation in Brodmann's areas 7A and 7B, the middle frontal gyrus, extra-striate cortex, the hand somastosensory cortex, and frontal cortex (Cohen et al.).


What is the theoretical basis for EMDR therapy?

Shapiro (1995) developed the Accelerated Information Processing model to describe and predict the effects of EMDR therapy. More recently, Shapiro (2001, 2018) expanded this into the Adaptive Information Processing (AIP) model to broaden its applicability. She hypothesizes that humans have an inherent information processing system that generally processes the multiple elements of experiences to an adaptive state where learning takes place. She conceptualizes memory as being stored in linked networks that are organized around the earliest related event and its associated affect. Memory networks are understood to contain related thoughts, images, emotions, and sensations. The AIP model hypothesizes that if the information related to a distressing or traumatic experience is not fully processed, the initial perceptions, emotions, and distorted thoughts will be stored as they were experienced at the time of the event. Shapiro argues that such unprocessed experiences become the basis of current dysfunctional reactions and are the cause of many mental disorders. She proposes that EMDR therapy successfully alleviates mental disorders by processing the components of the distressing memory. These effects are thought to occur when the targeted memory is linked with other more adaptive information. When this occurs, learning takes place, and the experience is stored with appropriate emotions able to guide the person in the future.


Studies reported in this paper have been supported by grants from the following foundations and granting agencies: the Lundbeck Foundation (to Ron Kupers), the European Union (Grant IST-2001-38040 and IST-2006-027141 to Pietro Pietrini), the Italian Ministry of Education, University and Research (PRIN RBNE018ET9-003, 200411841, and 2006117208 to Pietro Pietrini), Fondazione IRIS, Castagneto Carducci (Livorno, Italy to Pietro Pietrini), the Danish Medical Research Council (to Maurice Ptito), and the Harland Sanders Foundation (to Maurice Ptito). Pietro Pietrini and Emiliano Ricciardi wish to thank the Unione Italiana Ciechi for its support to the blindness research program, and the MRI Laboratory at the Fondazione “Gabriele Monasterio” Regione Toscana/CNR (Pisa, Italy).

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Keywords: vision, blindness, consciousness, qualia, cross-modal plasticity, supramodality, rewiring

Citation: Kupers R, Pietrini P, Ricciardi E and Ptito M (2011) The nature of consciousness in the visually deprived brain. Front. Psychology 2:19. doi: 10.3389/fpsyg.2011.00019

Received: 23 November 2010 Paper pending published: 04 January 2011
Accepted: 25 January 2011 Published online: 14 February 2011.

Morten Overgaard, Aarhus University, Denmark

Ryota Kanai, University College London, UK
Steven Laureys, University of Liège, Belgium

Copyright: © 2011 Kupers, Pietrini, Ricciardi and Ptito. This is an open-access article subject to an exclusive license agreement between the authors and Frontiers Media SA, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are credited.


Haptic perception: A tutorial

This tutorial focuses on the sense of touch within the context of a fully active human observer. It is intended for graduate students and researchers outside the discipline who seek an introduction to the rapidly evolving field of human haptics. The tutorial begins with a review of peripheral sensory receptors in skin, muscles, tendons, and joints. We then describe an extensive body of research on “what” and “where” channels, the former dealing with haptic perception of objects, surfaces, and their properties, and the latter with perception of spatial layout on the skin and in external space relative to the perceiver. We conclude with a brief discussion of other significant issues in the field, including vision-touch interactions, affective touch, neural plasticity, and applications.

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