How attention affects border ownership in early visual areas.

Editor's Note: These short, critical reviews of recent papers in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to summarize the important findings of the paper and provide additional insight and commentary. For more information on the format and purpose of the Journal Club, please see Review of Fang et al. The classic problem of figure-ground segregation draws from a more general problem of determining the side to which the border belongs. The one-sided assignment of the border to regions is termed as " border ownership " and the region to which the border is assigned is perceived as the figure (Nakayama et al., 1989). There is considerable evidence to show that figure-ground assignment is not completed before the influence of spatial attention, thereby resulting in mutual interactions possibly through inputs from higher visual areas (Vecera et al., 2004). Fang et al. (2009) elegantly demonstrated that attention modulates border ownership in early visual areas. Fang et al. (2009) used functional magnetic resonance imaging (fMRI) adaptation to investigate whether the neural population in V1 and V2 are selective for border ownership and whether its processing is influenced by inputs from higher visual areas. Attention was manipulated by two separate tasks that used stimuli whose contextual information determined the border ownership [Fang et al. (2009), their Fig. 1]. The stimuli used for the experimental condition were square-wave radial-grating annulus with bright and dark alternating stripes. Either the bright or the dark stripes were longer in the radial direction, both inwards and outwards, causing the borders to be assigned to the bright or the dark regions, respectively. The control condition used stimuli in which figure-ground distinction was not possible. A trial began with an adaptation period followed by the test stimulus interleaved by blank interval. In one-third of the trials, the test stimulus differed from the adapting stimulus resulting in change in border ownership (different trial). In the rest of the trials, the adapting stimulus was either the same as the test stimulus (same trials) or followed by only blank intervals without any test stimulus (blank trials). In the attention-demanding task, the observers were asked to detect a transient change in luminance of the fixation point that occurred randomly throughout the trial. During the less demanding task, the observers had to identify the test stimulus (bright border or dark border) at the end of the trial. Event-related averages of …