Response latencies to the onset and offset of visual stimuli

Simple response times (RTs) are known to be slower to the offset of a visua l stimulus than to its onset. This is called the onset advantage. In the fi rst of four experiments, we discovered that a spurious onset advantage can be produced by the long persistence of P31 phosphor. In the remaining three experiments, we found that offset RTs were slower only when they were made in a context in which responses to the abrupt onset of some stimuli had to be suppressed. We tested this hypothesis of response suppression in two wa ys: (1) by mixing regular onset trials with other trials on which a respons e to an onset had to be suppressed, and (2) by ramping the emergence of "of fset" stimuli over time, so that offsets were the only abrupt events in the display. In both cases, we found that the onset advantage depended critica lly on whether the responses were made in a context of response suppression . We conclude that the onset advantage is mediated not by sensory factors s uch as visible persistence, but by response programming factors that are st rongly affected by contextual events.