P3 amplitude attenuation secondary to increases in target-to-target interval (TTI) during spatial serial order recall: implications for EEG models of working memory function.

Research suggests that increasing delays in stimulus read-out can trigger declines in serial order recall accuracy due to increases in cognitive demand imposed by the delay; however, the exact neural mechanisms associated with this decline are unclear. Changes in neural resource allocation present as the ideal target and can easily be monitored by examining changes in the amplitude of an ERP component known as the P3. Changes in P3 amplitude secondary to exogenous pacing of stimulus read-out via increased target-to-target intervals (TTIs) during recall could reflect decreased neural resource allocation due to increased cognitive demand. This shift in resource allocation could result in working memory storage decay and the declines in serial order accuracy described by prior research. In order to examine this potential effect, participants were administered a spatial serial order processing task, with the recall series consisting of a series of correct ('match') or incorrect ('non-match' or 'oddball') stimuli. Moreover, the recall series included either a brief (500 ms) or extended (2000 ms) delay between stimuli. Results were significant for the presence of a P3 response to non-match stimuli for both experimental conditions, and attenuation of P3 amplitude secondary to the increase in TTI. These findings suggest that extending the delay between target recognition could increase cognitive demand and trigger a decrease in neural resource allocation that results in a decay of working memory stores.