Abstract
Studies on cognitive effort have shown that pupil dilation is a reliable indicator of memory load. However, it is conceivable that there are other sources of effort involved in memory that also affect pupil dilation. One of these is the ease with which an item can be retrieved from memory. Here, we present the results of an experiment in which we studied the way in which pupil dilation acts as an online marker for memory processing during the retrieval of paired associates while reducing confounds associated with motor responses. Paired associates were categorized into sets containing either 4 or 7 items. After learning the paired associates once, pupil dilation was measured during the presentation of the retrieval cue during four repetitions of each set. Memory strength was operationalized as the number of repetitions (frequency) and set-size, since having more items per set results in a lower average recency. Dilation decreased with increased memory strength, supporting the hypothesis that the amplitude of the evoked pupillary response correlates positively with retrieval effort. Thus, while many studies have shown that “memory load” influences pupil dilation, our results indicate that the task-evoked pupillary response is also sensitive to the experimentally manipulated memory strength of individual items. As these effects were observed well before the response had been given, this study also suggests that pupil dilation can be used to assess an item’s memory strength without requiring an overt response.
Highlights
The size of the pupil has repeatedly been shown to vary systematically with cognitive effort
Another potential source of cognitive effort as indexed by the pupillary response is retrieval effort. This relative difficulty is typically deduced from reaction times and accuracy measures that are thought to reflect the strength of the memory traces on retrieval processes (e.g., [9]) and the influence of contextual effects (e.g., [10,11])
The goal of the present study was to assess whether and how the memory strength of information retrieved from memory influences pupil dilation while reducing possible confounds associated with response execution
Summary
The size of the pupil has repeatedly been shown to vary systematically with cognitive effort (see e.g., [1] for a review). Van Gerven et al [3] and Karatekin [4] let participants memorize lists of serially presented digits and observed an increase in pupil dilation for each additional digit, and Granholm [5] showed that the pupil dilated with increased sequence length in digit span tasks until all cognitive capacity is used, after which the pupillary response decreased Another potential source of cognitive effort as indexed by the pupillary response is retrieval effort We varied frequency and recency to test whether retrieval-evoked pupil dilation is sensitive to the relative strength of the retrieved item’s memory trace
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