Seeing an Auditory Object: Pupillary Light Response Reflects Covert Attention to Auditory Space and Object

Attention to the relevant object and space is the brain's strategy to effectively process the information of interest in complex environments with limited neural resources. Numerous studies have documented how attention is allocated in the visual domain, whereas the nature of attention in the auditory domain has been much less explored. Here, we show that the pupillary light response can serve as a physiological index of auditory attentional shift and can be used to probe the relationship between space-based and object-based attention as well. Experiments demonstrated that the pupillary response corresponds to the luminance condition where the attended auditory object (e.g., spoken sentence) was located, regardless of whether attention was directed by a spatial (left or right) or nonspatial (e.g., the gender of the talker) cue and regardless of whether the sound was presented via headphones or loudspeakers. These effects on the pupillary light response could not be accounted for as a consequence of small (although observable) biases in gaze position drifting. The overall results imply a unified audiovisual representation of spatial attention. Auditory object-based attention contains the space representation of the attended auditory object, even when the object is oriented without explicit spatial guidance.