Eye Movements in the “Morris Maze” Spatial Working Memory Task Reveal Deficits in Strategic Planning

Analysis of eye movements can provide insights into processes underlying performance of cognitive tasks. We recorded eye movements in healthy participants and people with idiopathic Parkinson’s disease during a token foraging task based upon the spatial working memory (SWM) component of the widely used CANTAB test battery. Participants selected boxes (using a mouse click) to reveal hidden tokens. Tokens were never hidden under a box where one had been found before, such that memory had to be used to guide box selections. A key measure of performance in the task are Between Search Errors (BSEs) in which a box where a token has previously been found is selected again. Eye movements were found to be most commonly directed towards the next box to be clicked on, but fixations also occurred at rates higher than expected by chance on boxes further ahead or back along the search path. Looking ahead and looking back in this way was found to correlate negatively with BSEs and was significantly reduced in Parkinson’s patients. Refixating boxes where tokens had already been found correlated with BSEs and the severity of Parkinson’s disease symptoms. It is concluded that eye movements can provide an index of cognitive planning in the task. Refixations on locations where a token has been found may also provide a sensitive indicator of visuo-spatial memory integrity. Eye movement measures derived from the SWM task may prove useful in the assessment of executive functions, neurological and psychiatric disease in the future