Dynamics of Visual Feature Integration and Decision Making

The human brain analyzes a visual object first by basic feature detectors. These features are integrated in subsequent stages of the visual hierarchy. Generally it is assumed that the information about these basic features is lost once the information is send to the next stage in the visual hierarchy. To investigate the time course of feature integration I used transcranial magnetic stimulation (TMS) and the feature fusion paradigm. In feature fusion, two stimuli that differ in one feature are presented in rapid succession such that they are not perceived individually but as one single stimulus only. The fused percept is an integration of the features of both stimuli. Here, I show that, first, the original feature information persists in the visual system for a surprisingly long time. Second, the neural representations of the features interact when the two are integrated into a fused percept, but not when they are perceptually separated. Third, the "window of integration" within which features can be integrated spans about 100 ms and forth, the integration process precedes not only consciousness but also decision making.