Figure-ground interaction in the human visual cortex

Abstract

Discontinuities in feature maps serve as important cues for the location of object boundaries. Here we used multi-input nonlinear analysis methods and EEG source imaging to assess the role of several different boundary cues in visual scene segmentation. Synthetic figure/ground displays portraying a circular figure region were defined solely by differences in the temporal frequency of the figure and background regions in the limiting case and by the addition of orientation or relative alignment cues in other cases. The use of distinct temporal frequencies made it possible to separately record responses arising from each region and to characterize the nature of nonlinear interactions between the two regions as measured in a set of retinotopically and functionally defined cortical areas. Figure/background interactions were prominent in retinotopic areas, and in an extra-striate region lying dorsal and anterior to area MT+. Figure/background interaction was greatly diminished by the elimination of orientation cues, the introduction of small gaps between the two regions, or by the presence of a constant second-order border between regions. Nonlinear figure/background interactions therefore carry spatially precise, time-locked information about the continuity/discontinuity of oriented texture fields. This information is widely distributed throughout occipital areas, including areas that do not display strong retinotopy.

The Selectivity of Task-Dependent Attention Varies with Surrounding Context

“…This suggests that the stimulus differences across the four configurations were small enough to leave the strength of suppression from the center to surround unchanged. Our findings are similar to those of Appelbaum et al (2008) who measured SSVEPs to a center and surround configuration reversing at different frequencies as a function of the gap between them. They showed that the frequency-tagged response to the center, whose size was fixed, was independent of gap size, which parallels our finding that the fixed-size surround evokes similar responses in all configurations regardless of gap size in the ignored condition.…”

“…Our choice of gap size and phase offset was based on previous research that shows that the interaction between center and surround configurations varies as a function of gap size and degree of phase offset. This interaction was greatest for abutting gratings and was negligible by a gap size of 0.2° (Xu et al, 2005;Appelbaum et al, 2008). Thus we expect a weak interaction (if any) at a gap size of 0.1°and no significant interaction at a gap size of 0.25°.…”

Neural evidence for competition-mediated suppression in the perception of a single object

“…One set of theories and models posit that two adjacent regions compete for object status (Craft et al, 2007;Grossberg, 1994;Kienker et al, 1986;Sejnowski & Hinton, 1987) with the winner perceived as the object, and the loser perceived as a shapeless ground. There has been some debate regarding whether neural responses are facilitated for perceived objects (Appelbaum, Wade, Vildavski, Pettet, & Norcia, 2006;Appelbaum, Wade, Pettet, Vildavski, & Norcia, 2008;Lamme, 1995), suppressed for grounds (Likova & Tyler, 2008;Peterson & Skow, 2008;Salvagio et al, 2012;Tsotsos, Culhane, Kei Wai, Lai, Davis, & Nuflo, 1995), or whether both effects occur (Strother et al, 2012). Here, our use of retinotopic mapping and precise localization of the cortical representations of the figure and ground allowed us to provide supporting evidence for ground suppression as a mechanism behind object perception.…”

The time course of shape discrimination in the human brain

“…In the interest of brevity, we provide an overview of these methods, and reference the reader to our previous work (Ales and Norcia, 2009;Appelbaum and Norcia, 2009;Appelbaum et al, 2006Appelbaum et al, , 2008 for a more a more detailed description.…”