Microsaccade direction reveals the variation in auditory selective attention processes.

Abstract

Selective spatial attention plays a critical role in perception in the daily environment where multiple sensory stimuli exist. Even covertly directing attention to a specific location facilitates the brain's information processing of stimuli at the attended location. Previous behavioral and neurophysiological studies have shown that microsaccades, tiny involuntary saccadic eye movements, reflect such a process in terms of visual space and can be a marker of spatial attention. However, it is unclear whether auditory spatial attention processes that are supposed to interact with visual attention processes influence microsaccades and vice versa. Here, we examine the relationship between microsaccade direction and auditory spatial attention during dichotic oddball sound detection tasks with human participants of both sexes. The results showed that the microsaccade direction was generally biased contralateral to the ear to which the oddball sound was presented or that to which sustained auditory attention was directed. The post-oddball modulation of microsaccade direction was associated with the behavioral performance of the detection task. The results suggest that the inhibition of stimulus-directed microsaccade occurs to reduce erroneous orientation of ocular responses during selective detection tasks. We also found that the correlation between microsaccade direction and neural response to the tone originated from the auditory brainstem (frequency-following response: FFR). Overall, the present study suggests that microsaccades can be a marker of auditory spatial attention and that the auditory neural activity fluctuates over time with the states of attention and the oculomotor system, also involving the auditory subcortical processes.Significance statement Microsaccades, tiny involuntary saccadic eye movements, reflect covert visual attention and influence neural activity in the visual pathway depending on the attention states. However, we lack convincing evidence of whether and how microsaccades reflect auditory spatial attention and/or neural activity along the auditory pathway. Intriguingly, we showed that the microsaccade direction exhibited systematic stimulus-related change and correlated with auditory brainstem frequency-following response (FFR) during the dichotic selective attention task. These results suggest that microsaccades are associated with general spatial attention processes, not restricted to the visual domain, and can be a good tool for accessing fluctuating neural activity that may covary with the attention states.