The persistence of global form (Part II): Figure-specific fMRI activity in V1

Abstract

In Part I we showed persistence-related activity in V1. Was this activity localized to the retinotopic location of the figure? If so, this would suggest that higher-tier visual areas facilitate the representation of figure-specific visual information in V1.We measured fMRI activity in V1 during the visual persistence of global forms. We used global forms of three different sizes in two different experiments: an eccentricity-localizer and the main persistence experiment. The purpose of the eccentricity-localizer was to identify three retinotopic locations (ROIs) in V1, each of which would correspond to the eccentricity of the figures used in the persistence experiment. The purpose of the persistence experiment was to assess the relationship between persistence-related fMRI activity and figure size (eccentricity). We observed a sustained increase in fMRI activity (persistence) in ROIs that corresponded to the size of a given figure. Activity was reduced in the remaining two ROIs, indicating suppression. That is, we observed fMRI responses retinotopically such that increases in fMRI activity corresponding to a maintained representation of figure were delineated from background-specific decreases in fMRI activity (related to the suppression of the background). Part I suggested that higher-tier visual areas influence activity in V1 via feedback. The results presented here suggest that this influence is specific to the retinotopic location of the figure, which explains why previous studies (prior to Part I) failed to observe persistence in V1. These studies used large early visual ROIs that included both sustained fMRI activity (persistence) and reduced fMRI activity (suppression), which combined to produce a null effect. More importantly, our present results are consistent with a recurrent processing account of figure-ground segregation that predicts which image regions are preferentially perceived as figure or as background.