SPATIAL SCALE-DEPENDENT IN-PHASE AND ANTIPHASE DIRECTIONAL BIASES IN THE PERCEPTION OF SELF-ORGANIZED MOTION PATTERNS

A long row of evenly spaced dots is displaced on successive frames by half the distance between the dots. Although these stimuli are directi onally ambiguous, spatially and temporally coherent unidirectional and oscillatory motion patterns are perceived as a result of the temporal persistence of competing in-phase and anti-phase directional biases, respectively. The perceiver's spatial scale is critical is determining whether dots are near enough to favor an in-phase bias or far enough apart to favor an anti-phase bias. The results are explained by a diff erential-gradient model of cooperative interaction, which specifies th at the strength of facilitating (excitatory) interactions among motion detectors with similar directional selectivity falls off with distanc e at a greater rate than the strength of competing inhibiting interact ions.