The influence of an auditory accessory stimulus on saccadic responses to multiple visual targets

K.E. Troidl1, H. Colonius1,2

1Graduiertenkolleg Psychoakustik, Universität Oldenburg, Germany (e-mail:karine@uni-oldenburg.de);
2SFB Neurokognition, Universität Oldenburg, Germany

The effects of multiple visual stimuli on saccadic eye movements have been studied extensively. Saccades are systematically affected by stimulus properties such as intensity, size, and interstimulus spacing. (Findlay, 1982). The integration of auditory and visual stimuli became a topic of oculomotor research recently, since it is supposed that both modalities converge on SC. Auditory stimuli can facilitate responses to visual stimuli, particularly with both stimuli at the same spatial location (e.g., Colonius & Arndt, 1998). Most investigations on visual-auditory interaction have been restricted to situations with just one visual and one auditory stimulus. Here we investigate the influence of an auditory accessory on saccadic reaction times with multiple visual target stimuli. Subjects were instructed to make saccades toward any of two visual stimuli presented at an eccentricity of 8 deg or 24 deg to the right or left of fixation point. Additionally, via an virtual acoustic environment, an auditory stimulus (white noise) was presented at the same eccentricity of either visual stimulus and with a stimulus onset asynchrony (SOA) of -50, 0, or 50 ms. Although the subjects were allowed to ignore the white noise, it became obvious that the auditory accessory stimulus influenced the selection of the visual target. With the visual targets in opposite hemispheres, a significant bias toward the visual target accompanied by the auditory stimulus was observed, under all SOA's. However, if the visual stimuli appeared within the same hemisphere, the auditory stimulus had no influence on the selection process when subjects selected the more central target stimulus. On the level of saccadic reaction times, the auditory stimulus always had a facilitative effect. Eye movements were the faster the earlier the auditory stimulus was presented for both visual targets. Generally, these results support the idea of an integration of visual and auditory stimuli in a joint saliency map.