Opposing dorsal/ventral stream dynamics during figure-ground segregation

Abstract

The visual system has been commonly subdivided into two segregated visual processing streams: The dorsal pathway processes mainly spatial information, and the ventral pathway specializes in object perception. Recent findings, however, indicate that different forms of interaction cross-talk exist between the dorsal and the ventral stream. Here, we used TMS and concurrent EEG recordings to explore these interactions between the dorsal and ventral stream during figure-ground segregation. In two separate experiments, we used repetitive TMS and single-pulse TMS to disrupt processing in the dorsal V5/HMT+ and the ventral lateral occipital area stream during a motion-defined figure discrimination task. We presented stimuli that made it possible to differentiate between relatively low-level figure boundary detection from higher-level surface segregation processing steps during figure-ground segregation. Results show that disruption of V5/HMT+ impaired performance related to surface segregation; this effect was mainly found when V5/HMT+ was perturbed in an early time window 100 msec after stimulus presentation. Surprisingly, disruption of the lateral occipital area resulted in increased performance scores and enhanced neural correlates of surface segregation. This facilitatory effect was also mainly found in an early time window 100 msec after stimulus presentation. These results suggest a push-pull interaction in which dorsal and ventral extrastriate areas are being recruited or inhibited depending on stimulus category and task demands.