Maintaining fixation does not increase demands on working memory relative to free viewing

The comparison of memory performance during free and fixed viewing conditions has been used to demonstrate the involvement of eye movements in memory encoding and retrieval, with stronger effects at encoding than retrieval. Relative to conditions of free viewing, participants generally show reduced memory performance following sustained fixation, suggesting that unrestricted eye movements benefit memory. However, the cognitive basis of the memory reduction during fixed viewing is uncertain, with possible mechanisms including disruption of visual-mnemonic and/or imagery processes with sustained fixation, or greater working memory demands required for fixed relative to free viewing. To investigate one possible mechanism for this reduction, we had participants perform a working memory task—an auditory n-back task—during free and fixed viewing, as well as a repetitive finger tapping condition, included to isolate the effects of motor interference independent of the oculomotor system. As expected, finger tapping significantly interfered with n-back performance relative to free viewing, as indexed by a decrease in accuracy and increase in response times. By contrast, there was no evidence that fixed viewing interfered with n-back performance relative to free viewing. Our findings failed to support a hypothesis of increased working memory load during fixation. They are consistent with the notion that fixation disrupts long-term memory performance through interference with visual processes.