Two experiments investigated the neural mechanisms of Gestalt
grouping by recording high-density event-related brain potentials
(ERPs) during discrimination tasks. In Experiment 1, stimulus
arrays contained luminance-defined local elements that were
either evenly spaced or grouped into columns or rows based on
either proximity or similarity of shape. Proximity grouping
was indexed by a short-latency positivity (110–120 ms)
over the medial occipital cortex and a subsequent right
occipitoparietal negativity. Grouping by similarity was reflected
only in a long-latency occipitotemporal negativity. In Experiment
2, proximity grouping was examined when local elements were
defined by motion cues, and was again associated with a medial
occipital positivity. However, the subsequent long-latency
negativity was now enhanced over the left posterior areas. The
implications of these results to the neural substrates subserving
different grouping processes are discussed.