Abstract
Introduction: Task-evoked pupillary responses (TEPR) are a reliable measure of cognitive effort (Beatty, 1982). They vary systematically with working memory load (Kahneman & Beatty, 1966), up to a ceiling, when working memory capacity is reached (Granholm, et al., 1996). Our aim was to investigate whether the same pattern holds for in iconic memory. Methods: In each trial, five expert observers were presented with a set of differently-colored star-shaped items, spaced symmetrically around central fixation. Trials were blocked by set size, with either 4, 6, 8, or 10 items presented. After a 1000 ms exposure, a randomly chosen pair of neighboring items disappeared; this amounts to a zero-latency partial report post-cue. After 500 ms, the two items reappeared, with one changed to a new color and the other unchanged. Participants were instructed to look at the item that changed. Eye movements and pupil diameters were collected throughout the trial by a Tobii T120 eye tracker. Results and conclusions: When set size is below iconic memory capacity, performance on this task should be maximal. As set size exceeds capacity, performance should drop. Indeed, performance was near ceiling for up to 6 items, then started to decrease, pointing to a capacity of 6 items (see Blaser & Kaldy, 2010). However, unlike load-dependent TEPRs that were found in the working memory literature, TEPRs in this task did not increase with set size. In addition to this, there were no significant differences in TEPR between correct and incorrect trials (in set size 10), indicating that errors were caused by failures of memory retrieval, not effort. In short, increasing the load on iconic memory does not result in a concomitant pupil increase, suggesting that these increasing demands do not draw on the same set of cognitive resources demanded by working memory.
Meeting abstract presented at VSS 2013