Feature integration but not feature separation can be modulated by TMS

How the brain integrates visual information across time into coherent percepts is an open question. Here, we investigated this integration using a feature fusion paradigm. In feature fusion, two stimuli are presented in immediate succession. The stimuli are not perceived individually but as one fused stimulus. For example, a left and a right offset Vernier presented in rapid succession are perceived as one Vernier that is nearly aligned. It has been shown that feature fusion can be modulated by transcranial magnet stimulation (TMS) over the occipital cortex for a surprisingly long duration of 400 ms, showing that neural representations interact for this duration. Here, we show that these Vernier stimuli are perceived individually if separated by interstimulus interval (ISI) of only 20 ms. TMS has no effect on the perception of either of the two Verniers. If instead of an ISI a pattern mask is presented for 20 ms, Verniers fuse again and fusion can be modulated by TMS. Our results suggest that TMS can affect Vernier representations only when features are bound into one object, but not when the very same features belong to different objects. [Johannes Rüter is supported by the Swiss National Science Foundation]