Schematic representation of working memory formation. At each stage of the process, cognitive resources are allotted to attend to both relevant and non-relevant extraneous stimuli and target stimulus encoding can be diminished by increasing the salience of these non-target stimuli.

monkeys were resistant to the distracting effects of the stimulus. However, delayed recall in aged monkeys was markedly impaired by visual interference during delay intervals. A second key aspect of the methodologies described above is the salience of the stimuli presented during delay intervals. The stimuli in each of these paradigms can be characterized as irrelevant or task-irrelevant in relation to the target stimulus to be remembered. The issue, then, is recognition by the subjects of the salience or lack thereof of the stimulus they are exposed to during variable delay intervals, an issue which is likely to impact the severity of recall impairment. More specifically, in the position memory paradigm using lit panels, the distracting stimulus was a random illumination of all of the panels by a light of a different hue than the target light for the duration of the delay. Thus, monkeys were not exposed to stimuli during delays that may be perceived as potentially matching the target sample.17 Similarly, in the food reward paradigm, animals were exposed to stimuli during delays that were semantically and spatially distinct from the food reward placement.18

The latter study included an examination of the temporal relationship between distracting stimuli and cognitive processing during delay intervals. These authors assessed the relative distracting effects of the same stimuli presented either immediately after presentation of the target stimulus (start of delay interval), during the middle of the delay interval, or immediately before presentation of a response opportunity (end of delay interval). Using the task-irrelevant distracting stimuli in these studies, temporal position of the stimulus during the delay interval did not alter the distracting effect of the stimulus. This stands in contrast to what would be predicted based on the hypothesis that distractibility involves disruption of the transition from selective attention to consolidation, which would be reflected in distractors placed early in the delay interval producing markedly greater impairment of recall than those placed elsewhere temporally. However, only cognitively impaired aged animals were employed in this study and it remains to be seen if younger animals respond similarly.

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