Are your eyes following your thoughts? Exploring individual differences in internal coupling

The eyes are remarkably active during internal cognitive processes and often couple to internal events, but there is substantial interindividual variability in the amount of this internal coupling. These variations present considerable challenges for predicting cognitive states and raise important theoretical questions about their origins. This study explores whether internal coupling serves as a compensation mechanism to supports internal activities when task demands exceed individual's cognitive resources or if internal coupling occurs as a byproduct of mental imagery, with its co-occurrence determined by the quality of an individual's mental image. We examined how consistently eye movements aligned with imagined movement in a visuospatial working memory task and related these coupled saccades to measures of working memory capacity (Complex span tasks) and imagery skills (VVIQ, OSIVQ). We found that the rate of coupled saccades, when the task was performed entirely in mind, ranged from zero to 90 %. The data showed some indications that people with lower working memory capacity and lower vividness of visual imagination might benefit from internal coupling, hinting at some functional and compensatory role of coupling. However, these results were not robust, and no adaptive response to increased task demands was observed, challenging the notion of strategic use of internal coupling. The quality of mental imagery influenced internal coupling, with the removal of a visual spatial reference reducing coupling frequency, especially in those participants with lower spatial working memory capacity. Overall, while internal coupling is partly related to functional aspects and the quality of mental images, a substantial portion of individual differences remained unexplained, highlighting the need for further research into the role of eye movements during internal cognitive processes.