Neural correlates of boundary perception

Abstract

The responses of neurons in areas V1 (17) and V2 (18) of anesthetized and paralyzed rhesus monkeys and cats were recorded while presenting a set of computer-generated visual stimuli that varied in pattern, texture, luminance, and contrast. We find that a class of extrastriate cortical cells in cats and monkeys can signal the presence of boundaries regardless of the cue or cues that define the boundaries. These cue-invariant (CI) cells were rare in area V1 but easily found in V2. CI cortical cells responded more strongly to more salient boundaries regardless of the cue defining the boundaries. Many CI cortical cells responded to illusory contours and exhibited the same degree of orientation and direction selectivity when tested with boundaries defined by different cues. These cells have significant computational power inherent in their receptive fields since they were able to generalize across stimuli and integrate multiple cues simultaneously in order to signal boundaries. Cells in higher order cortical areas such as MT (Albright, 1992), MST (Geesaman & Anderson, 1996), and IT (Sary et al., 1993) have previously been reported to respond in a cue invariant fashion. The present results suggest that the ability to respond to boundaries in a cue-invariant manner originates at relatively early stages of cortical processing.

Electrophysiological indexes of illusory contours perception in humans

“…Our data do not seem to support the hypothesis of a striate cortex (V1) involvement in illusory contour perception (as suggested by Grosof et al [11], Hirsch et al [14] and Leventhal et al [22]). However, neurons signalling illusory boundaries are less numerous in V1 than in V2 [22], which might explain why a change in the activation pattern of V1 neurons is not easily detectable through scalp recordings of ERPs in humans.…”

“…More recently, cortical cells have been found in the extra-striate occipital areas signalling the presence of illusory defined boundaries in cats and monkeys [22]. According to the same study, cells with this property, although rare, were not totally absent in V1.…”

“…However, neurons signalling illusory boundaries are less numerous in V1 than in V2 [22], which might explain why a change in the activation pattern of V1 neurons is not easily detectable through scalp recordings of ERPs in humans. Our ERP data showed a significant trend, though not statistically significant, namely early sensory P1 response was affected by the presence of subjective contours (as suggested in the maps of Fig.…”

The direction-selective contrast response of area 18 neurons is different for first- and second-order motion

“…Stimuli defined by differences in derived properties such as contrast or texture ("second-order" stimuli- Chubb & Sperling, 1988;Cavanagh & Mather, 1989) also drive similarly stimulusselective responses in many early visual cortical neurons in cat areas 17018 (Zhou & Baker, 1993;Leventhal et al, 1998) and primate V1 (Chaudhuri & Albright, 1997). While neurons often respond more weakly to these second-order motion stimuli (e.g., Zhou & Baker, 1994) than to conventional luminance-defined ("first-order") bars or gratings, previous measurements of CRFs for these complex stimuli (O'Keefe & Movshon, 1998) examined neurons in area MT0V5 rather than early visual areas, and did not measure direction selectivity.…”

Edge Preserved Image Compression Using Extended Shearlet Transform

“…In order to achieve high compression ratio, most of the transform coding techniques use only low frequency components for compression. But in Human Visual system, selective neural cells have, undoubtedly, substantiated the perceptual importance of edges in an image (Marr and Ullman, 1981;Leventhal et al, 1998).…”