Preserved local but disrupted contextual figure-ground influences in an individual with abnormal function of intermediate visual areas.
Bottom Line: We found that contextual influences on figure-ground organization were selectively disrupted in LG, while local sources of figure-ground influences were preserved.Effects of object knowledge and familiarity on figure-ground organization were also significantly diminished.Our results suggest that the mechanisms mediating contextual and familiarity influences on figure-ground organization are dissociable from those mediating local influences on figure-ground assignment.
Affiliation: UCL Institute of Cognitive Neuroscience, University College London, 17 Queen Square, London WC1N 3AR, UK. firstname.lastname@example.orgShow MeSH
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Mentions: The mechanisms of familiarity influences on figure-ground organization have sparked debate. Some have suggested that object knowledge functions in a top-down, interactive manner (Vecera & O’Reilly, 1998, 2000) perhaps relying on feedback connections from shape-sensitive higher-order visual areas to border-ownership neurons in lower-order areas. Others have suggested that these influences may arise through early (106–156 ms: Trujillo, Allen, Schnyer, & Peterson, 2010) or bottom-up processing of familiarity cues (Peterson, 1999) and are dissociable from conscious object recognition (Peterson et al., 2000). Given LG's profoundly pathological function in intermediate visual areas and impaired object recognition, testing him provides an opportunity to assess the role of intermediate visual areas in familiarity influences on figure-ground organization. Accordingly, we showed him (and control participants) familiar and scrambled bipartite stimuli like those in Fig. 6A and B, adapted from previous work on figure-ground familiarity influences with normal observers (Peterson & Gibson, 1994a; Peterson et al., 2000; Peterson & Kim, 2001). We asked participants to indicate which side (left or right) was figural/in-front. In line with previous work, we expected controls to choose the side depicting the common object more often in the intact than the scrambled condition. If LG shows a similar difference between these two conditions, it would show preserved familiarity influences on figure-ground organization despite his object recognition difficulties and suggest that intermediate visual cortex has no necessary role in familiarity effects on figure-ground. To assess his explicit object recognition, subsequent to the figure-ground test we gave him an explicit naming task with the same exact edges used in the figure-ground task. However, in this explicit naming task, the edges did not appear in bipartite stimuli. Instead, each edge appeared as the edge of a single black region on a fully surrounding gray background (see Fig. 7). The explicit naming task also gave participants unlimited exposure time unlike the figure-ground task which had only a brief exposure (100 ms) in order to encourage first impression responses.
Affiliation: UCL Institute of Cognitive Neuroscience, University College London, 17 Queen Square, London WC1N 3AR, UK. email@example.com