Different mechanisms underlie three inhibitory phenomena in cat area 17

Abstract

Recently, it has been proposed that all suppressive phenomena observed in the primary visual cortex (V1) are mediated by a single mechanism, involving inhibition by pools of neurons, which, between them, represent a wide range of stimulus specificities. The strength of such inhibition would depend on the stimulus that produces it (particularly its contrast) rather than on the firing rate of the inhibited cell. We tested this hypothesis by measuring contrast-response functions (CRFs) of neurons in cat V1 for stimulation of the classical receptive field of the dominant eye with an optimal grating alone, and in the presence of inhibition caused by (1) a superimposed orthogonal grating (cross-orientation inhibition); (2) a surrounding iso-oriented grating (surround inhibition); and (3) an orthogonal grating in the other eye (interocular suppression). We fitted hyperbolic ratio functions and found that the effect of cross-orientation inhibition was best described as a rightward shift of the CRF ('contrast-gain control'), while surround inhibition and interocular suppression were primarily characterised as downward shifts of the CRF ('response-gain control'). However, the latter also showed a component of contrast-gain control. The two modes of suppression were differently distributed between the layers of cortex. Response-gain control prevailed in layer 4, whereas cells in layers 2/3, 5 and 6 mainly showed contrast-gain control. As in human observers, surround gratings caused suppression when the central grating was of high contrast, but in over a third of the cells tested, enhanced responses for low-contrast central stimuli, hence actually decreasing threshold contrast.

Different Signal Enhancement Pathways of Attention and Consciousness Underlie Perception in Humans

“…Because contrast-polarity sensitivity is predominantly found subcortically in LGN and in layer 4 in V1 (Hubel and Wiesel, 1968;Levitt et al, 2001), our findings are consistent with the idea that interocular suppression operates at early visual stages (Blake, 1989;Tong et al, 2006), potentially as early as LGN or V1 (Sengpiel et al, 1998;Polonsky et al, 2000;Meese and Hess, 2004;Watanabe et al, 2004;Haynes et al, 2005;Bahrami et al, 2008;Yuval-Greenberg and Heeger, 2013). However, other research suggests that interocular masking at LGN or V1 is weak or nonexistent (Lehky and Maunsell, 1996;Leopold and Logothetis, 1996;Macknik and Martinez-Conde, 2004;Keliris et al, 2010;Watanabe et al, 2011).…”

“…However, apart from afterimages, attention can decrease perception or performance in motion-induced blindness (Geng et al, 2007;Schölvinck and Rees, 2009) and the motion aftereffect (Murd and Bachmann, 2011), for Troxler/peripheral fading (Lou, 1999;De Weerd et al, 2006), visual memory (Voss and Paller, 2009), SF (Yeshurun and Carrasco, 1998, the attentional blink (Olivers and Nieuwenhuis, 2005), and visual search (Smilek et al, 2006). These findings suggest that our conclusions may be valid beyond the context of afterimages.…”

“…1 A, B). The influence of consciousness on CRFs is not yet known, although one of the techniques to modulate conscious perception, interocular suppression, often, but not always, produces contrast gain functions (Sengpiel et al, 1998;Watanabe et al, 2004;Bahrami et al, 2008;Yuval-Greenberg and Heeger, 2013).…”

Attention model of binocular rivalry

“…Neural activity in visual cortex, measured with single-cell electrophysiology, exhibits rivalry-like alternations (80,81), and neural responses in visual cortex also exhibit interocular suppression (82,83). However, some of these experiments were performed with anesthetized animals.…”

Improving vision in adult amblyopia by perceptual learning

“…Neuronal responses in the visual cortex are tuned for location, orientation, and spatial frequency. Recent evidence from studies in the cat and the monkey (20,(22)(23)(24)(25) shows that neuronal responses in the primary visual cortex are modulated by remote image parts, with both excitatory and inhibitory effects observed, depending on stimulus contrast and configuration. Psychophysical and electrophysiological results show abnormal interactions in amblyopic patients (6,7), with an extended range of inhibition.…”