The dynamics of bi-stable alternation in ambiguous motion displays: a fresh look at plaids.

Prolonged observations of moving plaids lead to bi-stable alternations between coherency and transparency. However, most studies of plaids used brief presentations and a 2AFC between the two interpretations, thus overlooking the dynamical aspect of plaid perception. In other domains, most notably binocular rivalry, it was shown that the dynamics of the bi-stable alternations reveal important insights about the underlying mechanisms. Here we develop methods to study the dynamics of plaid perception. Observers continually indicated their percept (coherency or transparency) during presentations that lasted 1-5 min. Two measures of the relative strength of the coherency percept were derived from those data: C/[C+T], the relative time spent seeing coherency, and RTtransp, the response time to report transparency. Those measures are independent of each other yet tightly correlated, and both show systematic relations to manipulations of plaid parameters. Furthermore, the two measures are sensitive to manipulations in wide parametric regimes, including ranges where brief-presentation methods suffer from "ceiling" and "floor" effects. We conclude that studying the dynamics of bi-stability in plaids can provide new and unsuspected findings about motion integration and segmentation.