Visual prepotency and eye orientation

Abstract

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...

Visual-auditory interaction in speeded classification: Role of stimulus difference

“…That is, the greater vulnerability of auditory classification to interference by orthogonal variation in an irrelevant visual stimulus, evident in the results of Melara and O'Brien, was probably not the fortuitous outcome of a mismatch in baseline levels of performance. Supporting the hypothesis of visual priority are findings obtained in cued RT tasks, in which visual and auditory stimuli, matched for subjective magnitude, have been presented together, showing that subjects respond predominantly to the visual stimulus, being unaware in some cases that the tone has even been presented (Colavita, 1974;Colavita, Tomko, & Weisberg, 1976;Colavita & Weisberg, 1979). This visual dominance was reduced but not abolished when the subjects were instructed to respond to the tones on conflicting trials, or when the tone was made twice as intense as the light (Colavita, 1974;Colavita et al, 1976).…”

Existence of competing modality dominances

“…In the original demonstration, Colavita (1974) presented participants with unimodal visual or auditory stimuli (a flash or a beep, respectively), with the instruction to respond as quickly as possible to either by pressing a designated response key (see also Colavita, Tomko, & Weisberg, 1976;Colavita & Weisberg, 1979;Egeth & Sager, 1977). The key analysis involved the error rate made on bimodal trials, where the instruction was to respond by pressing both unimodal (visual and auditory) response keys.…”

Familiarity of objects affects susceptibility to the sound-induced flash illusion

“…Visual dominance is a well-established phenomenon occurring when visual processing dominates over other sensory modalities as vision often constitutes the most reliable of the senses [6][7][8]10]. For example, in the ventriloquist effect [17] the observer perceives the auditory signal as emanating from the same location as the moving lips that he/she visually perceives.…”