The tactile integration of local motion cues is analogous to its visual counterpart

Abstract

The visual and somatosensory systems have been shown to process spatial information similarly. Here we investigate tactile motion processing using stimuli whose perceptual properties have been well established in vision research, namely superimposed gratings (plaids), barber poles, and bar fields. In both modalities, information about stimulus motion (speed and direction) conveyed by neurons at low levels of sensory processing is ambiguous, a conundrum known as the aperture problem. Our results suggest that the tactile perception of motion, analogous to its visual counterpart, operates in multiple stages: first, the perceived direction of motion is determined by a majority vote from local motion detectors, which are subject to the aperture problem. As in vision, the conflict between the cues from terminators and other local motion cues is gradually resolved over time so that the perceived direction approaches the veridical direction of motion.aperture problem ͉ psychophysics ͉ plaid ͉ barber pole ͉ somatosensory B oth vision and touch share the common problem of inferring stimulus form, texture, and motion from a spatiotemporal pattern of activation across a two-dimensional sensory sheet (i.e., the retina and skin). The two systems have been found to process information about two-dimensional spatial form in a similar fashion (1-3). In both systems, information about motion can be acquired by analyzing how stimulus contours change over time. Both the visual and somatosensory systems may therefore have evolved analogous mechanisms to process motion information as well. Then again, the analogy between the two systems is not absolute: for instance, depth ordering and transparency are problems that have no obvious analogue in the cutaneous sense (although palpation through gloves may involve a tactile equivalent of transparency). Furthermore, shear forces, which have no direct visual analogue, may contribute to the tactile perception of motion (4, 5). These differences between vision and touch may lead to differences in the way the two systems process motion.The study of motion processing provides an opportunity to address an important question in sensory neuroscience, namely: how is the environment represented at each stage of perceptual processing? Indeed, the speed and direction of motion of individual (one-dimensional) edges is ambiguous because information about the motion component parallel to their orientation is not available, a predicament known as the aperture problem (6) (Fig. 1). To acquire a veridical percept of an object's direction of motion, then, it is often necessary to integrate motion information across multiple stimulus contours that differ in orientation (7,8) or to rely on so-called terminators-such as end points, corners, and intersections-whose direction of motion is unambiguous (9, 10).The aperture problem is inherent to individual neurons at low levels of processing because these neurons have spatially restricted receptive fields and only ''see'' local contours of the stimulus. From the sta...

Visuotactile motion congruence enhances gamma-band activity in visual and somatosensory cortices

“…Our observation of effects in early sensory areas is intriguing when considering psychophysical evidence that the somatosensory system computes stimulus features such as orientation of edges and motion in a similar manner as the visual system Pei et al, 2008Pei et al, , 2010Pei et al, , 2011. This similarity between the two sensory systems could allow for motion signals to be integrated at an early level in the processing hierarchy.…”

Path integration in tactile perception of shapes

“…To form a global motion percept, the tactile system spatially integrates the local motion signals provided by primary afferents across the skin [4]. Accordingly, Pei and colleagues showed that the perceived direction of motion of a plaid surface (i.e., a surface formed by superimposing two gratings of different orientations) is the result of spatial integration of the different local motion components [5]. Conversely to decode the motion path of an object sliding over a fixed area of the skin, direction and speed information, which are directly available to the nervous system [6][7][8][9], would need to be integrated over time.…”

Steven Hsiao: In Memoriam

“…In fact, the direction signal conveyed by these neurons was invariant with other stimulus properties, including not only shape, but speed and amplitude as well. Steve and colleagues then measured the neuronal responses evoked by tactile analogs of stimuli that had been used to probe visual motion processing, including gratings, barberpoles, and random dot displays (Pei et al, 2008(Pei et al, , 2010(Pei et al, , 2011.…”