Cognitive Science Program

Vision is superior to touch in shape perception even with equivalent peripheral input (2015)
Yoonju Cho, James C Craig, Steven S Hsiao, Sliman J Bensmaia
Journal of Neurophysiology, 115 (1),

Abstract

Results from previous studies suggest that two-dimensional spatial patterns are processed similarly in vision and touch when the patterns are equated for effective size or when visual `stimuli are blurred to mimic the spatial filtering of the skin. In the present study, we measured subjects' ability to perceive the shape of familiar and unfamiliar visual and tactile patterns to compare form processing in the two modalities. As had been previously done, the two-dimensional tactile and visual patterns were adjusted in size to stimulate an equivalent number of receptors in the two modalities. We also distorted the visual patterns using a filter that accurately mimics the spatial filtering effected by the skin to further equate the peripheral images in the two modalities. We found that vision consistently outperformed touch regardless of the precise perceptual task and of how familiar the patterns were. Based on an examination of both the earlier and current data, we conclude that visual processing of both familiar and unfamiliar two-dimensional patterns is superior to its tactile counterpart except under very restricted conditions.

Perceptual Constancy of Texture Roughness in the Tactile System (2011)
Takashi Yoshioka, James C Craig, Graham Beck, Steven S Hsiao
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience, 31 (48), 17603-17611

Abstract

Our tactual perception of roughness is independent of the manner in which we touch the surface. A brick surface feels rough no matter how slowly or how rapidly we move our fingers, despite the fluctuating sensory inputs that are transmitted to the finger. Current theories of roughness perception rely solely on inputs from the cutaneous afferents, which are highly affected by scan velocity and force. The question then is: how is roughness constancy achieved? To this end, we characterized the subject's perceived roughness in six scanning conditions. These included two modes of touch: direct touch, where the finger is in contact with the surface, and indirect touch, where the surface is scanned with a hand-held probe; and three scanning modes: active (moving the hand across a stationary surface), passive (moving the surface across a stationary hand), and pseudo-passive (subject's hand is moved by the experimenter across a stationary surface). Here, we show that roughness constancy is preserved during active but not passive scanning, indicating that the hand movement is necessary for roughness constancy in both direct and indirect touch. Roughness constancy is also preserved during pseudo-passive scanning, which stresses the importance of proprioceptive input. The results show that cutaneous input provides the signals necessary for roughness perception and that proprioceptive input resulting from hand movement—rather than a motor efference copy—is necessary to achieve roughness constancy. These findings have important implications in providing realistic sensory feedback for prosthetic-hand users.

Neural Mechanisms of Tactile Motion Integration in Somatosensory Cortex (2011)
Y.C. Pei, Steven S Hsiao, James C Craig, Sliman J Bensmaia
Neuron, 69 (3), 536-547

Abstract

How are local motion signals integrated to form a global motion percept? We investigate the neural mechanisms of tactile motion integration by presenting tactile gratings and plaids to the fingertips of monkeys, using the tactile analogue of a visual monitor and recording the responses evoked in somatosensory cortical neurons. The perceived directions of the gratings and plaids are measured in parallel psychophysical experiments. We identify a population of somatosensory neurons that exhibit integration properties comparable to those induced by analogous visual stimuli in area MT and find that these neural responses account for the perceived direction of the stimuli across all stimulus conditions tested. The preferred direction of the neurons and the perceived direction of the stimuli can be predicted from the weighted average of the directions of the individual stimulus features, highlighting that the somatosensory system implements a vector average mechanism to compute tactile motion direction that bears striking similarities to its visual counterpart.

Shape Invariant Coding of Motion Direction in Somatosensory Cortex (2010)
Y.C. Pei, Steven S Hsiao, James C Craig, Sliman J Bensmaia
PLoS Biology, 8 (2),

Abstract

Invariant representations of stimulus features are thought to play an important role in producing stable percepts of objects. In the present study, we assess the invariance of neural representations of tactile motion direction with respect to other stimulus properties. To this end, we record the responses evoked in individual neurons in somatosensory cortex of primates, including areas 3b, 1, and 2, by three types of motion stimuli, namely scanned bars and dot patterns, and random dot displays, presented to the fingertips of macaque monkeys. We identify a population of neurons in area 1 that is highly sensitive to the direction of stimulus motion and whose motion signals are invariant across stimulus types and conditions. The motion signals conveyed by individual neurons in area 1 can account for the ability of human observers to discriminate the direction of motion of these stimuli, as measured in paired psychophysical experiments. We conclude that area 1 contains a robust representation of motion and discuss similarities in the neural mechanisms of visual and tactile motion processing.

Aging and tactile temporal order (2010)
James C Craig, Roger P Rhodes, Thomas Busey, Diane Kewley-Port
Attention Perception & Psychophysics, 72 (1), 226-235

Abstract

Although it is generally held that speed of processing declines with age, there have been few studies in which tactile temporal processing has been examined with older subjects. In the present study, temporal order judgments were obtained from a group of younger subjects (n = 28, mean age = 23.5 years) and a group of older subjects (n = 93, mean age = 69.8 years). The subjects judged the temporal order of two patterns presented to the same finger, four patterns presented to the same finger, and two patterns presented to different hands. Depending on the task, the average thresholds for the older subjects ranged from two to five times longer than the thresholds from the younger subjects. In absolute terms, the largest difference between the young and older subjects was seen in correctly identifying the order of four patterns, a difference of more than 500 msec. There was some support for the decline in temporal processing being due in part to a slowing in cognitive processing, and, depending on the task, in part to stimulus persistence and difficulty in pattern identification.

Convergence of Submodality-Specific Input Onto Neurons in Primary Somatosensory Cortex (2009)
Y.C. Pei, Peter Denchev, Steven S Hsiao, James C Craig
Journal of Neurophysiology, 102 (3), 1843-1853

Abstract

At the somatosensory periphery, slowly adapting type 1 (SA1) and rapidly adapting (RA) afferents respond very differently to step indentations: SA1 afferents respond throughout the entire stimulus interval (sustained response), whereas RA afferents respond only at stimulus onset (on response) and offset (off response). We recorded the responses of cortical neurons to step indentations and found many neurons in areas 3b and 1 to exhibit properties that are intermediate between these two extremes: These neurons responded during the sustained portion of the stimulus and also at the offset of the stimulus. Several lines of evidence indicate that these neurons, which exist in large proportions even at these early stages of somatosensory cortical processing, receive input from both populations of afferents. First, we show that many cortical neurons have both a significant sustained response and a significant off response. Second, the strength of the off response is uncorrelated with that of the sustained response, which is to be expected if sustained and off responses stem from different populations of afferent fibers. Third, the bulk of the variance in cortical responses to step indentations can be accounted for using a linear combination of both SA1 and RA responses. Finally, we show that the off response in cortical neurons does not reflect rebound from inhibition. We conclude that the convergence of modality specific input onto individual neurons is common in primary somatosensory cortex and discuss how this conclusion might be reconciled with previous findings.

The effects of age on sensory thresholds and temporal gap detection in hearing, vision, and touch (2009)
Larry E. Humes, Thomas Busey, James C Craig, Diane Kewley-Port
Attention Perception & Psychophysics, 71 (4), 860-871

Abstract

Differences in sensory function between young (n 5 42, 18—31 years old) and older (n 5 137, 60—88 years old) adults were examined for auditory, visual, and tactile measures of threshold sensitivity and temporal acuity (gap-detection threshold). For all but one of the psychophysical measures (visual gap detection), multiple measures were obtained at different stimulus frequencies for each modality and task. This resulted in a total of 14 dependent measures, each based on four to six adaptive psychophysical estimates of 75% correct performance. In addition, all participants completed the Wechsler Adult Intelligence Scale (Wechsler, 1997). Mean data confirmed previously observed differences in performance between young and older adults for 13 of the 14 dependent measures (all but visual threshold at a flicker frequency of 4 Hz). Correlational and principalcomponents factor analyses performed on the data from the 137 older adults were generally consistent with task and modality independence of the psychophysical measures.

Discriminating smooth from grooved surfaces: Effects of random variations in skin penetration (2008)
James C Craig, Roger P Rhodes, Gregory O Gibson, Sliman J Bensmaia
Experimental Brain Research, 188 (3), 331-340

Abstract

The ability to discriminate a smooth surface from a grooved one depends on several variables, including the width of the grooves and the force with which the skin is contacted. It has been hypothesized that this smooth–grooved discrimination with statically presented stimuli is based on intensity cues, namely, the overall difference in perceived intensity between the smooth and grooved surfaces. To test this hypothesis, the perceived intensities of test stimuli were varied on a trial-by-trial basis by varying the depth of penetration the contactor was allowed to travel into the skin. As compared to a control condition in which stimuli were presented with the same average penetration and contrary to the hypothesis, random variations in penetration produced no decline in smooth–grooved performance. The total amount of conformance was an accurate predictor of sensitivity across various penetrations and across two test sites (distal finger pad and finger base). It appears that subjects are making absolute rather than comparative judgments in the smooth–grooved task. A recently developed continuum mechanical model of the responses of first-order mechanoreceptive afferents to static stimuli provided both a good fit to the data and indicated what aspect of the peripheral neural image was relevant for discriminating smooth surfaces from grooved surfaces.

The Representation of Stimulus Orientation in the Early Stages of Somatosensory Processing (2008)
Sliman J Bensmaia, Peter Denchev, J Francis Dammann, James C Craig
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience, 28 (3), 776-786

Abstract

At an early stage of processing, a stimulus is represented as a set of contours. In the representation of form, a critical feature of these local contours is their orientation. In the present study, we investigate the representation of orientation at the somatosensory periphery and in primary somatosensory cortex. We record the responses of mechanoreceptive afferents and of neurons in areas 3b and 1 to oriented bars and edges using a variety of stimulus conditions. We find that orientation is not explicitly represented in the responses of single afferents, but a large proportion of orientation detectors (∼50%) can be found in areas 3b and 1. Many neurons in both areas exhibit orientation tuning that is preserved across modes of stimulus presentation (scanned vs indented) and is relatively insensitive to other stimulus parameters, such as amplitude and speed, and to the nature of the stimulus, bar or edge. Orientation-selective neurons tend to be more SA (slowly adapting)-like than RA (rapidly adapting)-like, and the strength of the orientation signal is strongest during the sustained portion of the response to a statically indented bar. The most orientation-selective neurons in SI are comparable in sensitivity with that measured in humans. Finally, responses of SI neurons to bars and edges can be modeled with a high degree of accuracy using Gaussian or Gabor filters. The similarity in the representations of orientation in the visual and somatosensory systems suggests that analogous neural mechanisms mediate early visual and tactile form processing.

A dense array stimulator to generate arbitrary spatio-temporal tactile stimuli (2007)
Justin H Killebrew, Sliman J Bensmaia, John F Dammann, Peter Denchev
The Journal of Neuroscience Methods, 161 (1), 62-74

Abstract

The generation and presentation of tactile stimuli presents a unique challenge. Unlike vision and audition, in which standard equipment such as monitors and audio systems can be used for most experiments, tactile stimuli and/or stimulators often have to be tailor-made for a given study. Here, we present a novel tactile stimulator designed to present arbitrary spatio-temporal stimuli to the skin. The stimulator consists of 400 pins, arrayed over a 1 cm2 area, each under independent computer control. The dense array allows for an unprecedented number of stimuli to be presented within an experimental session (e.g., up to 1200 stimuli per minute) and for stimuli to be generated adaptively. The stimulator can be used in a variety of modes and can deliver indented and scanned patterns as well as stimuli defined by mathematical spatio-temporal functions (e.g., drifting sinusoids). We describe the hardware and software of the system, and discuss previous and prospective applications.

The effect of force and conformance on tactile intensive and spatial sensitivity (2006)
Gregory O Gibson, James C Craig
Experimental Brain Research, 170 (2), 172-181

Abstract

The effect of force on intensive and spatial processing was examined with three measures of tactile sensitivity. One of the measures based on intensive cues is the smooth-grooved (SM/GV) task, and the two other measures based on spatial cues are the grating orientation and gap detection tasks. Measures were made at two locations that vary in sensitivity and in the density of innervation of the primary afferent fibers, the right index fingerpad and the palmar surface of the proximal phalanx (fingerbase). At each location, psychometric functions were generated for each of the three measures for two forces (50 and 200 g). The results indicated that increasing force led to marked improvement on the task that relied on intensive cues; however, on the tasks that relied on spatial cues, force had no effect on performance. Biomechanical measures were made of the depth to which the skin invades the grooves of the contactors (conformance) at the two test sites, with the two forces, and with different groove widths. Conformance was found to be a joint function of force and groove width. Further, performance on the SM/GV task could be predicted by the amount of conformance. The psychophysical results are consistent with the view that increasing conformance increases neural activity in the primary afferent fibers, and that this increase in neural activity improves SM/GV performance, but has little effect on the quality of the spatial image.

Visual motion interferes with tactile motion perception (2006)
James C Craig
Perception, 35 (3), 351-367

Abstract

Previous studies have demonstrated that visual apparent motion can alter the judgment of auditory apparent motion. We investigated the effect of visual apparent motion on judgments of the direction of tactile apparent motion. When visual motion was presented at the same time as, but in a direction opposite to, tactile motion, accuracy in judging the direction of tactile apparent motion was substantially reduced. This reduction in performance is referred to as ‘the congruency effect’. Similar effects were observed when the visual display was placed either near to the tactile display or at some distance from the tactile display (experiment 1). In experiment 2, the relative alignment between the visual and tactile directions of motion was varied. The size of the congruency effect was similar at 0° and 45° alignments but much reduced at a 90° alignment. In experiment 3, subjects made confidence ratings of their judgments of the direction of the tactile motion. The results indicated that the congruency effect was not due to subjects being unsure of the direction of motion and being forced to guess. In experiment 4, static visual stimuli were shown to have no effect on the judgments of direction of the tactile stimuli. The extent to which the congruency effect reflects capture effects and is the result of perceptual versus post-perceptual processes is discussed.

The crossed-hands deficit in tactile temporal-order judgments: The effect of training (2006)
Jamees C Craig, Adrienne N Belser
Perception, 35 (11), 1561-1572

Abstract

Several recent studies have shown that judgments of temporal order for tactile stimuli presented to the two hands are greatly affected by crossing the hands. The size of the threshold for judging temporal order may be up to four times larger with the hands crossed as compared to the hands uncrossed. The results from these recent studies suggest that with crossed hands, contrary to many situations involving the integration of tactile and proprioceptive information, subjects have difficulty in adjusting their perception of tactile inputs to correspond with the spatial positions of the hands. In the present study we examined the effect of training in judging temporal order on the size of this crossed-hands deficit—the difference in the thresholds for temporal-order judgments when the hands are crossed and uncrossed. All training procedures produced significant declines in the size of the deficit. With training, the difference between crossed-hands and uncrossed-hands temporal-order thresholds dropped from several hundred milliseconds to as little as 19 ms. A group of percussionists with experience in playing with crossed hands showed the same crossed-hands effects as non-musicians. The results were consistent in showing that the crossed-hands deficit was never completely eliminated but was greatly reduced with training. The implication is that subjects are able to adjust to the crossed-hands posture with modest amounts of training. The results are discussed in terms of the explanations that have been offered for the crossed-hands deficit.

Tactile spatial sensitivity and anisotropy (2005)
Gregory O Gibson, James C Craig
Perception & Psychophysics, 67 (6), 1061-1079

Abstract

A gap detection task was examined for its usefulness as a measure of tactile spatial sensitivity and as a measure of anisotropy. In Experiment 1, sensitivity was measured with a gap detection task both with and without a latex glove at three locations on the hand: the fingerpad, fingerbase, and palm. Results showed that sensitivity varied as a function of location and was correlated with changes in the density of innervation of the primary afferent fibers. In accord with other measures of spatial sensitivity, the glove had a moderate effect on sensitivity in the gap detection task. The results both with and without the glove were more similar to those obtained using another measure of spatial sensitivity, the grating orientation task, than to those obtained using the smooth-grooved task, which is considered an intensive measure. In Experiments 2-4, anisotropy was examined using the gap detection and grating orientation tasks, as well as the smooth-grooved task. Locations on the index finger, palm, and arm were tested. Results indicated that anisotropy was revealed only by tasks that relied on spatial cues. The differences between spatial sensitivity measured in the proximal-distal orientation as compared with the lateral-medial orientation varied by location and were as much as 2.35/1. The results are discussed in terms of what they may reveal about the underlying mechanisms responsible for tactile anisotropy.

The trajectory effect in intermodal temporal order judgments (2005)
James C Craig
Perception, 34 (3), 357-370

Abstract

Subjects judged which one of two patterns, a visual or a tactile pattern, had been presented first. The visual and tactile displays were placed in close spatial proximity. The patterns appeared to move across their respective displays. Although irrelevant to the temporal order judgment (TOJ), the direction of motion of the patterns—the trajectory—affected the judgments. When the leading pattern was moving towards the trailing pattern (consistent movement), subjects tended to judge it, correctly, as leading. When the leading pattern was moving away from the trailing pattern (inconsistent movement), subjects tended to judge it, incorrectly, as trailing. Changing the spatial position of the arrays such that the pattern trajectories were no longer towards one another eliminated the effect of movement on TOJs. Although there was a substantial difference in performance on consistent and inconsistent trials, there were no differences in subjects' ratings of their performances. The results demonstrate that the trajectory effect can be obtained multimodally. The issues whether the effect of motion alters the perceived temporal separation between the visual and tactile patterns, and whether the visual and tactile patterns are represented by a common framework, are discussed.