The neurophysiology of figure-ground segregation in primary visual cortex

Abstract

The activity of neurons in the primary visual cortex of the awake macaque monkey was recorded while the animals were viewing full screen arrays of either oriented line segments or moving random dots. A square patch of the screen was made to perceptually pop out as a circumscribed figure by virtue of differences between the orientation or the direction of motion of the texture elements within that patch and the surround. The animals were trained to identify the figure patches by making saccadic eye movements towards their positions. Almost every cell gave a significantly larger response to elements belonging to the figure than to similar elements belonging to the background. The figure- ground response enhancement was present along the entire extent of the patch and was absent as soon as the receptive field was outside the patch. The strength of the effect had no relation with classical receptive field properties like orientation or direction selectivity or receptive field size. The response enhancement had a latency of 30–40 msec relative to the onset of the neuronal response itself. The results show that context modulation within primary visual cortex has a highly sophisticated nature, putting the image features the cells are responding to into their fully evaluated perceptual context.

The role of oscillatory brain activity in object processing and figure–ground segmentation in human vision

“…These different schemes may explain the 490 opposing power changes in gamma reported here. While opposing power changes in 491 gamma within the same visual area have not been reported before, we note that previous 492 studies on figure-ground segregation have reported either increases (Lamme, 1995; 493…”

“…The role of gamma rhythms in figure-ground segregation is hypothesised to result from 486 one or two general processes: (i) region labelling, achieved by labelling corresponding 487 elements in an isomorphic surface representation (Lamme, 1995); and/or (ii) border 488 ownership coding, achieved through contour representation following the activity of 489 orientation-selective units (Craft, et al, 2007). These different schemes may explain the 490 opposing power changes in gamma reported here.…”

“…For example, studies on figure-ground coding in monkey V1 have reported 498 enhanced spike rates within an object"s surface representation (Lamme, 1995;Zipser, et 499 al., 1996). On the other hand, multi-unit cellular recording in non-human primates showed 500 strong decoupling of population activity across a figure/ground border (Gail, et al, 2000).…”

Occipital network for figure/ground organization

“…The essence of Wgure/ ground organization is to assign an increased salience to the Wgure relative to the ground regions. In contrast to neurophysiological studies (e.g., Lamme 1995), to date no fMRI study has reported a response that is retinotopically matched with an arbitrary Wgure shape, in the absence of diVerentiating local cues.…”

“…In terms of neural architecture, does the mechanism employ lateral interactions (e.g., Gerrits and Vendrik 1970;Grossberg and Mingolla 1985;Grossberg 1994;Baek and Sajda 2005;Pao et al 1999;Zhaoping 2005), top-down feedback (e.g., Lamme and Roelfsema 2000;Lamme et al 2002;Roelfsema et al 2002;Craft et al 2007) or more sophisticated combinations? In terms of its coding mechanism, do the Wgure/ground conWgurations use border-based coding (e.g., von der Heydt et al 2003Heydt et al , 2005Craft et al 2007) or region-based coding (e.g., Lamme 1995;Zipser et al 1996;Lamme et al 1998;Super et al 2001;Roelfsema et al 2002)?…”