Front-back asymmetries in endogenous auditory spatial attention.

Research on endogenous auditory spatial attention typically uses headphones or sounds in the frontal hemispace, which undersamples panoramic spatial hearing. Crossmodal attention studies also show that visual information impacts spatial hearing and attention. Given the overlap between vision and audition in frontal space, we tested the hypothesis that the distribution of endogenous auditory spatial attention would differ when attending to the front versus back hemispace. Participants performed a non-spatial discrimination task where most sounds were presented at a standard location, but occasionally shifted to other locations. Auditory spatial attention cueing and gradient effects across locations were measured in five experiments. Accuracy was greatest at standard versus shift locations, and was comparable when attending to the front or back. Reaction time measures of cueing and gradient effects were larger when attending to the front versus back midline, a finding that was evident when the range of spatial locations was 180° or 360°. When participants were blindfolded, the front/back differences were still present. Sound localization and divided attention tasks showed that the front/back differences were attentional, rather than perceptual, in nature. Collectively, the findings reveal that the impact of endogenous auditory spatial attention depends on where attention is being focused.