Abstract
Simple decisions about features or properties of visual stimuli have been shown to involve a process of accumulating noisy sensory information over time, until a criterion amount of information has been attained and a decision can be made. High-resolution sensory information is accessible for several hundred milliseconds following stimulus offset (iconic memory), and may therefore act as a further source of evidence from which information is accumulated. In this study, we asked participants to make a series of simple judgments as to whether coherent motion in a random-dot stimulus was moving left or right (2AFC). Participants responded either immediately (speed-accuracy trade-off), after a varying blank delay (100–800 ms), or after a masked delay (100–800 ms). We found that when participant's post-stimulus responses were delayed by viewing a blank screen, decision accuracy improved for up to 400 ms. However, when the blank screen was replaced by a sensory masking stimulus, which has been shown to interfere with iconic memory, accuracy was significantly lower. The results of this study suggest that we can continue to accumulate evidence from an iconic store in the absence of a physical stimulus, and hence improve decision accuracy. Furthermore, the rate at which evidence is accumulated from a memory representation of the stimulus was found to match the rate of evidence accumulation during stimulus viewing.