Listening shapes seeing: Sustained auditory spatial attention enhances early visual-cortical processing

How does the auditory system implement spatial selection without a dedicated cortical map for space? One hypothesis holds that auditory spatial attention draws on a supra-modal network including the parietal-occipital cortex; an alternative implicates subcortical structures (e.g., superior colliculus) with no direct recruitment of visual cortex. To adjudicate between these accounts, we used a dichotic listening paradigm and tested whether sustained auditory spatial attention produces the behavioral and neural signatures of visual spatial attention, which would only be expected if auditory attention engages the same cortical mechanisms. Participants listened to two digit streams, spoken by male and female voices, played from left and right speakers. They were instructed to attend to either the left stream, the right stream, or a specific voice gender. A behavioral experiment (N=24) showed higher discrimination accuracy for visual stimuli appearing intermittently at the auditorily attended relative to unattended location. Furthermore, participants gaze was reliably biased towards the attended location. In a second experiment (N=14), we used electrophysiological recordings of frequency-tagged visual evoked potentials to more directly assess early visual processing, and found enhanced visual-cortical responses for stimuli matching the location of the attended auditory stream. In addition, occipital alpha power (8-11 Hz) was reduced over the hemisphere contralateral to the attended sound stream. Together, these effects mirror the hallmarks of visual-spatial attention, suggesting that auditory spatial attention co-opts the architecture of the visual cortex to implement spatial selection, thereby directly enhancing visual processing. Significance statementHuman can effortlessly direct spatial attention to a sounds location in the external world. Yet the auditory system has no dedicated spatial map in the brain, raising a fundamental question: how does auditory spatial attention arise? We show that sustained attention to a sound based on its location produces well-known signatures of visual spatial attention: enhanced visual-perceptual sensitivity, larger early visual-cortical responses, and modulation of occipital alpha-band activity and oculomotor behavior. This converging behavioral and neural evidence demonstrates that auditory spatial attention actively engages and reshapes early visual processing, pointing to a supra-modal attention system shared across the senses.