Modality-dependant attentional control in human sound localization

Rudolf Andoga1, Martin Bernát1, Beáta Tomoriová1, and Norbert Kop?o1,2
1 Technical University of Košice, Letná 9, 04001 Košice, Slovakia
2 Boston University, 677 Beacon St., Boston, MA 02215
rudolf.andoga@tuke.sk, tomorib@alternet.sk, kopco@bu.edu

A behavioral experiment was performed to determine 1) whether a priori information influences sound localization, and 2) whether the influence depends on the modality through which the information is provided. Sound localization performance was measured for transient auditory stimuli coming from one of ten locations, spaced from 
-90° to 90° in the frontal horizontal plane of the listener. In most runs, a cue preceded the stimulus and indicated the hemisphere (left vs. right) from which the subsequent stimulus arrived. The cues differed by modality (visual: arrow shown on a computer screen, or auditory: lateralized tone), informativeness (cue predicted the target side correctly on 100%, 80%, or 50% of trials), and by the stimulus onset asynchrony (SOA) between the cue and the target (400, 800, and 1600 ms). The listeners were instructed to focus their attention to the side indicated by the cue. 

The effect of cue was evaluated by computing the mean response and the standard deviation in the responses with and without the cue. Independent of modality, a cue that indicated an incorrect side biased the responses towards its side, i.e., medially. A cue that indicated the target side correctly had an effect that depended on the cue modality: while the auditory cue still caused a medial bias, the visual cue caused the opposite, lateral bias that grew with increasing SOA. The information provided by the cue never decreased the standard deviation in responses. However, a visual cue that indicated an incorrect side caused a consistent increase in the responses at the largest SOA. 

These results indicate that the mechanisms that control auditory spatial attention are modality dependent and that they operate on relatively long time scales.