Abstract
The integration of information gained through various sensory modalities enables living organisms to execute motor acts rapidly. The purpose of the study was to examine how effectively visual cues can be integrated for the rapid generation of saccadic eye movements. Previous work has established that when saccadic eye movements are made to singly appearing visual targets, a bimodal distribution of saccadic latencies is often obtained, the first mode of which has been termed “express saccades.”
In this study we examined the rapidity with which saccadic eye movements can be generated to auditory and visual cues when they are presented singly and in combination. The visual display presented on a monitor consisted of a fixation spot which was followed by a single visual target that appeared either to the left and or to the right of the fixation spot. The auditory cue was provided through one of two speakers positioned to the left and right of the monitor. Eye movements were recorded enabling us to obtain a distribution of saccadic latencies. Data obtained from one of the monkeys we have studied showed 5% express saccades to singly appearing visual targets, 1% express saccades to singly presented auditory cues but 36% express saccades when single visual and auditory cues were presented together. Statistical analyses showed these effects to be highly significant (p <0.001). Similar results were obtained in another monkey.
The results establish that auditory and visual cues can be effectively integrated to produce a much higher percentage of express saccades than that obtained to visual and auditory cues alone. Having previously established that following superior colliculus inactivation express saccades are eliminated, we believe that this structure is likely to play a significant role in the integration of visual and auditory information for saccadic eye-movement generation.