Effects of Temporal Expectations on the Perception of Motion Gestalts.

Gestalt psychology has traditionally ignored the role of attention in perception, leading to the view that autonomous processes create perceptual configurations that are then attended. More recent research, however, has shown that spatial attention influences a form of Gestalt perception: the coherence of random-dot kinematograms (RDKs). Using ERPs, we investigated whether temporal expectations exert analogous attentional effects on the perception of coherence level in RDKs. Participants were presented fixed-length sequences of RDKs and reported the coherence level of a target RDK. The target was indicated immediately after its appearance by a postcue. Target expectancy increased as the sequence progressed until target presentation; afterward, remaining RDKs were perceived without target expectancy. Expectancy influenced the amplitudes of ERP components P1 and N2. Crucially, expectancy interacted with coherence level at N2, but not at P1. Specifically, P1 amplitudes decreased linearly as a function of RDK coherence irrespective of expectancy, whereas N2 exhibited a quadratic dependence on coherence: larger amplitudes for RDKs with intermediate coherence levels, and only when they were expected. These results suggest that expectancy at early processing stages is an unspecific, general readiness for perception. At later stages, expectancy becomes stimulus specific and nonlinearly related to Gestalt coherence.