Detection of stimulus change: The hypothetical roles of visual transient responses

Two random-dot patterns (D1 and D2) were displayed briefly in close temporal succession, separated by an interstimulus interval (ISI). The two patterns were identical except that D2 could contain one more element (addition) or one less element (subtraction) than D1. Observers were required to detect the addition or subtraction using a two-alternative forced-choice method. Three experiments were designed to examine Phillips and Singer’s (1974) suggestion that detection of additions and subtractions can be explained in terms of neural ON and OFF responses. Experiment 1 replicated Phillips and Singer’s finding that performance is progressively impaired as the ISI is increased. In Experiment 2, sudden shifts in luminance between D1 and D2 were combined with several durations of ISI to produce transient responses in a novel manner. Experiment 3 explored the roles of transient neural responses and of configurational changes as determinants of performance. Most predictions based on Phillips and Singer’s model were confirmed by the experimental outcomes. Some discrepancies between theory and data are noted, and directions for further research are suggested.