How do pupillary light responses and microsaccades allude to voluntary and involuntary auditory attention?

Pupillary light responses (PLR) and microsaccades allude to voluntary and involuntary visual attention, presumably reflecting the function of the frontal eye field and superior colliculus. In line with such allusion to visual attention, we recently found that PLR corresponds to the luminance condition of the voluntarily attended auditory space and object (Liao et al., 2023). This suggests a common audio-visual spatial attention mechanism underlying the neural circuits controlling eye movements. The current study further examines how PLR and microsaccades allude to voluntary and involuntary auditory attention using the same stimuli. Data from Liao et al. (2023) were reanalyzed to investigate the effect of voluntary attention on microsaccades and compare the PLR result with that induced by involuntary attention. To probe involuntary attention, we applied the Posner cueing paradigm. A task-irrelevant yet salient noise burst was presented to the left or right ear (or location) via headphones (or loudspeakers) before the target sound. Participants identified the target sound as quickly as possible while ignoring the noise distractor. Behavioral results confirmed an involuntary attentional shift to the distractor, as evidenced by faster reaction times when the target was presented on the same side as the distractor than when it was presented on the opposite side. Pupillary response, in contrast to the finding relating to voluntary auditory attention in Liao et al. (2023), showed little to no significant difference corresponding to the luminance condition where the distractor was presented. Microsaccades were found to occur in the same direction as the voluntarily attended sound and involuntarily attended distractor at different timings. Opposite microsaccadic directional bias was found only to the distractor, suggesting inhibition of return. These findings suggest an interaction between the top-down modulation and sound-driven attentional orienting underlying the microsaccade-generation system. The PLR reflects voluntary auditory attention but not involuntary auditory attention.