Human Ss matched an auditory and a visual stimulus for subjective magnitude. Then each stimulus was used as a cue in a reaction time task. On occasions when both stimuli were presented simultaneously, Ss' responding was seen to be dominated by the visual stimulus. Of further interest was the finding that on some occasions of simultaneous light-tone presentation Ss were unaware that the tone had been presented. This apparent prepotency of the visual over the auditory stimulus was seen to persist across a variety of experimental conditions, which included giving Ss verbal instructions to respond to the tone when both stimuli were presented simultaneously.Organisms are constantly exposed to a contiguous array of stimuli rather than to the isolated action of a single stimulus. Of this array, certain stimuli are more likely to be attended to than others. Such stimuli may be called prepotent for that particular organism. It has been shown, for example, that cats will attend only to the auditory component of a compound CS made up of a soft low tone and a bright flashing light. Thus, sound stimuli appear to be prepotent over light stimuli for the cat (Jane, Masterton, & Diamond, 1965).The four experiments described below represent a comparison ofthe auditory and visual modalities as to sensory prepotency for one of the most frequently used Ss in psychological research, the college freshman. EXPERIMENT IExperiment I involved observing the behavior that occurred when Ss were simultaneously presented with an auditory and a visual stimulus of equal subjective intensity, each of which had a characteristic response associated with it. MethodTen freshman psychology students at the University of Pittsburgh served as Ss. The group was composed of six males and four females. In a dimly illuminated room, each S was seated 4S em in front of a 30-cm-sq stimulus panel containing a S-cm speaker and a 6-W incandescent light source. Each S first matched an auditory and a visual stimulus for subjective intensity by adjusting the light with a Powerstat variable autotransformer until it was as bright as a . 4,OOO-Hz, 6S-dB SPL tone was loud. Then the matched stimuli were used as cues in a reaction time (RT) task.Each S placed his index fingers over two telegraph keys located directly in front of him. One key was designated as the "tone key," while the other was called the "light key." The right key was the tone key for five Ss, and the left key was the tone key for the remaining five Ss. There was one left-handed S in each condition. *This research was supported by U.S. Public Service Grant NS09027-03 from the National Institute of Neurological Diseases and Stroke. The author is indebted to Ross Perilman, who ran the Ss in Experiment II.S was instructed to press the tone key as soon as he heard the tone, or the light key as soon as he saw the light. A keypress terminated the stimulus. Light and tone onsets were manually controlled by E. A Standard timer measured RTs in milliseconds. After four practice trials, each S was given 30 simple RT...

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When simultaneously presented with a brief auditory and a brief visual stimulus of equal subjective magnitude, human subjects show a strong tendency to respond to the visual stimulus. The present experiments attempted to reduce or abolish this prepotency effect by manipulating the subject's visual fixation point, based upon the idea that eye orientation plays an important part in attending to either a brief auditory or a brief visual stimulus. The results suggested that visual prepotency in human subjects persists even when· peripheral rather than foveal vision is used.A recent series of experiments (Colavita, 1974) has demonstrated a strong visual prepotency in human subjects when they are placed in a conflict situation where they must respond to either a brief light stimulus or a brief tone stimulus. In these experiments, subjects matched an auditory and a visual stimulus for subjective magnitude. Then, each stimulus was used as a cue in a reaction time (RT) task_ On occasions when both stimuli were presented simultaneously, the subject's responding was seen to be dominated by the visual stimulus even when verbal instructions were given to respond to the tone in such instances. An interesting secondary finding was the fact that on some of the trials involving simultaneous lighttone presentations subjects were unaware that the tone had been presented.An attempt was made to explain the above results by referring to Broadbent's (1958) channel-switching model of information processing and attention. This model predicts that two simultaneously presented stimuli cannot be processed as effectively as the same two stimuli presented in succession. However, additional explanation is required for the fact that the visual channel is apparently sampled first by human subjects_We have proposed that for simultaneously presented auditory and visual stimuli of short duration, the resulting reflexive orienting response would more likely favor the visual rather than the auditory input. This proposal was based upon some evidence (Ades, 1944) that in the case of brief auditory and visual stimuli, the orienting response may ultimately involve the neural connections of the superior colliculus with the motor centers of the ventral tegmentum, medulla, and spinal cord. Thus, the visual channel might be sampled first by virtue of its more direct connections with the superior colliculus.Implicit in the above proposal is the idea that eye orientation plays an integral part in attending to either a brief auditory stimulus or a brief visual stimulus_ Thus, the visual prepotency noted in our RT task may be due to the fact that subjects are already fixating their gaze on the light source in anticipation of its being activated_ The two experiments reported below attempt to manipulate visual prepotency by altering subjects' visual ftxation point. EXPERIMENT IExperiment I was designed to measure sensory prepotency in a choice RT situation when the subject was instructed to use as a visual ftxation point a spot midway between the sound source an...

When human subjects are presented a light and a tone simultaneously, each of which serves as a cue in a reaction time task, responding is predominantly to the light. This phenomenon has been referred to as visual dominance. The present experiment attempted to test the hypothesis that when subjects must divide their attention between different objects in space, the visual channel is favored over the auditory channel. Rather than the "free-field" method used in our earlier work, our procedure involved the use of earphones to deliver the auditory stimulus. The results provided a further indication of the robustness of the visual dominance effect. While there was a slight reduction in the magnitude of the effect, as compared with the "free-field" situation, responding was still predominantly to the visual stimulus. 261Previous studies conducted in our laboratory over the past several years have demonstrated that when human subjects are presented a light and a tone sirnultaneously, each of which individually serves as a cue in a reaction time (RT) task, subjects respond predominantly to the light. This visual dominance effect is seen to persist when the subjective intensity of the tone is double that of the light (Colavita, 1974) , when subjects are given verbal instructions to respond to the tone rather than to the light (Colavita, 1974), when the tone source rathe r than the light source is used as a visual fixation point (Colavita, Tomko , & Weisberg, 1976) , and when subjects are required to respond to stimulus offset rather than stimulus onset (Colavita & Weisberg, 1979) _ The purpose of the present experiment was to explore a further aspect of this visual dominance effect . More specifically, we wished to test the idea that the subject has a finite amount of attention to direct to objects in space and that, for some reason, the visual channel receives a disproportionate amount of this quantity, to the detriment of attention to auditory events in space.We felt that one way to test this idea would be to deliver the auditory stimulus directly to the subject's ears via earphones rather than "free field," as had been the method of tone presentation used in our earlier experiments. The use of earphones should free the subject from the necessity of attending to the location of the tone in space and , possibly, bring about some change in the visual dominan ce effect.Simple tonal RT is generally reported to be faster than simple light RT. However, in the case of simultaneous light-tone presentation (what we call conflict trials), the subject's responding is dominated by the visual stimulus. Possibly, freeing the subject from the task of dividing his or her attention between two points in space (i.e., the sound source and the light source) through the use of earphones will reduce or abolish the visual dominance effect due to the greater speed of simple tonal RT over simple visual RT. On the other hand , the Copyright 1982 The Psychonomic Society , Inc. use of earphones might permit the subject to direct all of his or he...

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