Differential Effects of Visual and Auditory Cognitive Tasks on Smooth Pursuit Eye Movements.

Smooth pursuit eye movements (SPEM) are important to gather visual information that guides our interactions with moving objects (e.g., tracking a tennis ball, or following a car when driving). In many neurological conditions, from Parkinson's disease to stroke, the voluntary control of SPEM can be compromised. Therefore, SPEMs can serve as sensitive proxies for assessing cognitive and sensorimotor function. Prior research has shown that SPEMs are influenced by attention and working memory load, yet it remains unclear how the sensory modality of concurrent tasks interacts with these effects. Here, we conducted a 3 (working memory load: no load, easy [low load], and hard [high load]) × 2 (sensory modality: visual vs. auditory) experiment to examine how working memory load and secondary task modality interact to affect SPEM in healthy young adults. Participants tracked a moving circle while simultaneously performing an arithmetic task, where they added either constant (1) or variable (1-5) numbers which were presented visually or auditorily. Our results showed that a secondary auditory task increased tracking variability during high cognitive load. In contrast, we found that the visual task improved tracking, reducing variability irrespective of cognitive load. We interpret our results as evidence that auditory processing requires additional top-down control that is critical for the control of smooth pursuit, diverting resources required for smooth pursuit and, consequently, increasing SPEM variability. These findings emphasize the importance of sensory modality in understanding the interactions between working memory and oculomotor control. We suggest that auditory secondary cognitive tasks may provide a more sensitive test of sensorimotor control deficits in future research with clinical populations.