Abstract
One of the challenging task for the human visual system is how they extract and integrate the local elements from the cluttered background into the global contour perception. Although previous studies have suggested the involvement of both striate and extrastriate cortex for this intermediate-level processing of visual perception, their relative roles and dynamic interactions between these areas are largely unknown. To examine whether the recurrent processing between the lower and higher-level visual areas plays a causal role in contour integration, we applied fMRI-guided transcranial magnetic stimulation (TMS) on early visual cortex (V1/V2) and intermediate-level visual area (V3B) at four SOAs (60/80, 90/110, 120/140 or 150/170 ms) (plus a no-TMS condition) while the participants performed a contour detection task. Results showed that both V1/V2 and V3B were critically involved in the process of contour integration. Importantly, the first critical inference time window for V1/V2 (120/140 ms, p < .05, Cohen's d = 0.57) follows that for V3B (90/110 ms, p < .05, Cohen's d = 0.58). The inference effect was also found at 150/170 ms for both areas (V1/V2: p = .05, Cohen's d = 0.50; V3B: p = .08, Cohen's d = 0.41). These findings suggested that the critical contribution of V3B to contour integration was earlier than that of V1/V2. The present study provides direct evidence supporting the causal role of the recurrent processing between V3B and V1/V2 in contour integration and agree with the data from monkey physiology. Our findings fit well with the incremental grouping theory (Roelfsema, 2006; Roelfsema & Houtkamp, 2011), in which a feedforward sweep generates a coarse template in higher visual areas with large receptive fields before the processing of detail information in lower visual areas with small receptive field through feedback mechanisms.
Meeting abstract presented at VSS 2017