Microsaccade Direction Reveals the Variation in Auditory Selective Attention Processes.

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 (MSs), 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 MSs and vice versa. Here, we examine the relationship between MS direction and auditory spatial attention during dichotic oddball sound detection tasks with human participants of both sexes. The results showed that the MS 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 postoddball modulation of MS direction was associated with the behavioral performance of the detection task. The results suggest that the inhibition of stimulus-directed MSs occurs to reduce erroneous orientation of ocular responses during selective detection tasks. We also found that the correlation between MS direction and neural response to the tone originated from the auditory brainstem (frequency-following response). Overall, the present study suggests that MSs 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 auditory subcortical processes.