Abstract
Human vision briefly retains a trace of a stimulus after it disappears. This trace—iconic memory—is often believed to be a surrogate for the original stimulus, a representational structure that can be used as if the original stimulus were still present. To investigate its nature, a flicker-search paradigm was developed that relied upon a full scan (rather than partial report) of its contents. Results show that for visual search it can indeed act as a surrogate, with little cost for alternating between visible and iconic representations. However, the duration over which it can be used depends on the type of task: some tasks can use iconic memory for at least 240 ms, others for only about 190 ms, while others for no more than about 120 ms. The existence of these different limits suggests that iconic memory may have multiple layers, each corresponding to a particular level of the visual hierarchy. In this view, the inability to use a layer of iconic memory may reflect an inability to maintain feedback connections to the corresponding representation.
Highlights
It has long been known that human vision retains a brief trace of any stimulus it encounters
Error rates were much the same for all cadences, indicating that no speed-accuracy trade-offs occurred. These results indicate that the information in iconic memory can survive without serious degradation for at least 240 ms, consistent with conclusions obtained elsewhere (e.g., Sperling, 1960; Graziano and Sigman, 2008)
GENERAL DISCUSSION The results above indicate that for all visual search tasks, iconic memory can act as a surrogate for about 120 ms: during this time it can be used as and effectively as if the original stimulus were present
Summary
The duration over which it can be used depends on the type of task: some tasks can use iconic memory for at least 240 ms, others for only about 190 ms, while others for no more than about 120 ms The existence of these different limits suggests that iconic memory may have multiple layers, each corresponding to a particular level of the visual hierarchy. In this view, the inability to use a layer of iconic memory may reflect an inability to maintain feedback connections to the corresponding representation
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