Contrast dependence of contextual effects in primate visual cortex

Abstract

The responses of neurons in the visual cortex to stimuli presented within their receptive fields can be markedly modulated by stimuli presented in surrounding regions that do not themselves evoke responses. This modulation depends on the relative orientation and direction of motion of the centre and surround stimuli, and it has been suggested that local cortical circuits linking cells with similar stimulus selectivities underlie these phenomena. However, the functional relevance and nature of these integrative processes remain unclear. Here we investigate how such integration depends on the relative activity levels of neurons at different points across the cortex by varying the relative contrast of stimuli over the receptive field and surrounding regions. We show that simply altering the balance of the excitation driving centre and surround regions can dramatically change the sign and stimulus selectivity of these contextual effects. Thus, the way that single neurons integrate information across the visual field depends not only on the precise form of stimuli at different locations, but also crucially on their relative contrasts. We suggest that these effects reflect a complex gain-control mechanism that regulates cortical neuron responsiveness, which permits dynamic modification of response properties of cortical neurons.

Contextual Masking of Oriented Lines: Interactions Between Surface Segmentation Cues

“…A distinct CRF stimulus, in contrast, yielded relief from suppression. Numerous subsequent studies have confirmed these effects (e.g., Cavanaugh et al 2002;Lamme 1995;Levitt and Lund 1997;Li et al 2000;Zipser et al 1996). These results reveal that similar effects occur for luminance contrast polarity.…”

“…These responses are often modulated by the copresence of stimuli surrounding the CRF (Allman et al 1985;Blakemore and Tobin 1972;Das and Gilbert 1999;DeAngelis et al 1994;Kapadia et al 1995;Knierim and van Essen 1992;Lamme 1995;Levitt and Lund 1997;Li and Li 1994;Maffei and Fiorentini 1976;Nelson and Frost 1978;Zipser et al 1996). These modulatory effects parallel many well-known examples of the influence of context on visual perception .…”

“…1) is a potent cue for perceptual segmentation (Bergen and Julesz 1983;Caputo 1996;Foster and Westland 1995;Li et al 2000) and has a marked influence over orientation judgments (Mareschal et al 2001;Sekuler 1965;Wehrhahn et al 1996;Westheimer et al 1976). Similarly, responses to oriented CRF stimuli have been found to be stronger in the presence of textured surrounds that promote perceptual segmentation (orthogonal lines) than in the presence of surrounds that do not promote segmentation (parallel lines) (Cavanaugh et al 2002;Fries et al 1977;Gilbert and Wiesel 1990;Knierim and van Essen 1992;Lamme 1995;Levitt and Lund 1997;Li et al 2000;Nelson and Frost 1978;Zipser et al 1996).…”

Attention and contrast differently affect contextual integration in an orientation discrimination task

“…That is, the perceived orientation of the target was shifted towards the orientation of the context bars. Contrast-dependent switching of contextual influences has also been demonstrated by a number of physiological studies (Levitt and Lund 1997;Polat et al 1998;Mizobe et al 2001), but have not, to our knowledge, been reported systematically in a psychophysical setting.…”

TiViPE Simulation of a Cortical Crossing Cell Model

“…This non classical surround provides input from a larger portion of the visual scene than originally thought, permitting integration of information at early levels in the visual processing stream. Recent works indicate that neuronal surround modulation at cross-orientation, an orientation orthogonal to the preferred orientation of the CRF, play a key role in intermediate-level visual tasks, such as perceptual pop-out [14], contrast facilitation [3,20], and contextual modulation [8,4,5], and could endow neurons with a graded specialization for processing angular visual features such as corners and junctions [18,4].…”