Abstract
Human and macaque observers can detect and discriminate visual forms defined by differences in texture. The neurophysiological correlates of visual texture perception are not well understood and have not been studied extensively at the single-neuron level in the primate brain. We used a novel family of texture patterns to measure the selectivity of neurons in extrastriate cortical area V2 of the macaque (Macaca nemestrina, Macaca fascicularis) for the orientation of texture-defined form, and to distinguish responses to luminance- and texture-defined form. Most V2 cells were selective for the orientation of luminance-defined form; they signaled the orientation of the component gratings that made up the texture patterns but not the overall pattern orientation. In some cells, these luminance responses were modulated by the direction or orientation of the texture envelope, suggesting an interaction of luminance and texture signals. We found little evidence for a "cue-invariant" representation in monkey V2. Few cells showed selectivity for the orientation of texture-defined form; they signaled the orientation of the texture patterns and not that of the component gratings. Small datasets recorded in monkey V1 and cat area 18 showed qualitatively similar patterns of results. Consistent with human functional imaging studies, our findings suggest that signals related to texture-defined form in primate cortex are most salient in areas downstream of V2. V2 may still provide the foundation for texture perception, through the interaction of luminance- and texture-based signals.
Highlights
Information about visual form is signaled by different cues
We measured the orientation-selective responses of neurons in monkey area V2 to texture-defined form using texture patterns that allowed us to distinguish responses to luminance and texture cues
We report results from 128 V2 neurons recorded in nine macaque monkeys
Summary
Information about visual form is signaled by different cues. Forms signaled by differences in luminance are termed “first order.”. Forms signaled by differences in texture, such as changes in orientation or contrast, are termed “second order” if they exclude overall luminance changes. Little is known about the neurophysiological correlates of texture perception in the primate brain, at the level of individual neurons. Human fMRI studies have implicated high-level areas in the ventral visual pathway, reporting differential activation to displays containing texture boundaries in areas V4, TEO, and LOC (Grill-Spector et al, 1998; Kastner et al, 2000). Orientation-selective responses to texturedefined form are modest in early visual areas, increasing gradually along the pathway, and strongest in ventral occipital cortex (Larsson et al, 2006). Neurons in V2 have been shown to be selectively sensitive to a number of visual features more com-
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