The present article critically reviews the literature on the intersensory bias that results when the information available to different sensory modalities is caused to be discrepant. The characteristics for which discrepant sensory information has been provided include spatial location, shape, size/length, and orientation. Stimulus variables that affect the magnitude of intersensory bias are (a) structural factors, such as amount of discrepancy, active versus passive placement of the limb, and timing of the stimulus information, and (b) cognitive factors, such as subjects' awareness of the intersensory discrepancy, their assumption of the unitariness of the event being perceived, and the "compellingness" of the stimulus situation. Response variables that affect intersensory bias are the type and timing of the response required of the subjects. The evidence on developmental trends and individual differences in the susceptibility to intersensory bias is both sparse and conflicting. Also unclear is the relationship between intersensory bias and adaptation to perceptual rearrangement. None of the various theories-modality precision, directed attention, and modality appropriateness-accounts for all of the intersensory discrepancy results. Consequently, a new model is proposed, based on the supposition that intersensory bias is a result of an attempt by the perceptual system to maintain a perceptual experience consonant with a unitary event.Adult human perception is, for the most part, fully developed, very accurate, and served by a multiplicity of redundant cues. As a consequence, much of our current understanding of perceptual processes has come about when these processes have, for one reason or another, malfunctioned. Color blindness and congenital cataracts are examples of perceptual failures that have revealed a great deal about certain aspects of normal vision. Since such naturally occurring events are relatively rare, however, it has become a common procedure to deliberately interfere with the perception of otherwise normal human observers. The study of illusions is the best

Artificial discrepancy was created between information about azimuth coming from different sense modalities. The resolution of this discrepancy was examined for the cases of vision and proprioception, proprioception and audition, and vision and audition. Vision biases proprioceptive and auditory judgments. Proprioception biases auditory judgments and has a small effect on visual judgments. The results suggest that the combinations of sense modalities do not behave as an integrated system and the data are interpreted as indicating that different processes are involved in the resolution of discrepant directional information from different pairs of modalities.There has been considerable recent interest in the interactions of the various sense modalities. One technique that has been especially exploited is the creation of an artificial discrepancy between the information originating from one stimulus object but entering the organism via two modalities. Attention has been focused both on the initial reaction to the discrepancy (Is the information from one modality dominant over the other?) and on the subsequent adjustment to the discrepancy (Can one modality be said to accommodate to the other?). In much of the research the two modalities have been vision and proprioception and the discrepancy has involved visual distortion of a variety of stimulus dimensions, e.g., size (Rock & Victor, 1964), inclination (Klein, 1966), and spatial direction or azimuth (Hay, Pick, & Ikeda, 1965).The present study is an investigation of the initial reaction to a discrepancy between sense modalities in information about spatial direction. It ex tends to other pairs of sense modalities, our earlier work that included only vision and proprioception. The purpose of the presen t study was first to determine how the discrepancy of information coming from two sense modalities was resolved. For example, are there different degrees of bias or dominance that information coming from one modality has on different other modalities? Secondly, its purpose was to determine if a number of sense modalities functioned as a system. Specifically, would it be possible to predict the interaction of two modalities, knowing how each interacted with a third? Spatial direction was chosen as the contextual problem for this investigation since directional information is obtainable with relatively high precision via the three modalities of vision, proprioception, and audition.The basic design of the present study was a straightforward replication of one previous experiment that involved a discrepancy in azimuth between vision and proprioception (Hay, Pick, & Ikeda, 1965). In the presen t study there were three experiments that included a discrepancy between proprioception and audition, and between vision and audition, as well as the original discrepancy between vision and proprioception. In the original study Ss were asked to view their own finger (held passively on a shelf) through a prism that optically displaced its lateral position approximately 11 deg. The ...

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A magnitude estimation response procedure was used to evaluate the strength of visualauditory intersensory bias effects under conditions of spatial discrepancy. Major variables were the cognitive compellingness of the stimulus situation and instructions as to the unity or duality of the perceptual event. With a highly compelling stimulus situation and single-event instructions, subjects showed a very high visual bias of audition, a significant auditory bias of vision, and a sum of bias effects that indicated that their perception was fully consonant with the assumption of a single perceptual event. This finding reopens the possibility that the spatial modalities function as a transitive system, an outcome that Pick, Warren, and Hay (1969) had expected but did not obtain. Furthermore, the results support the model for intersensory interaction proposed by Welch and Warren (1980) with respect to the susceptibility of intersensory bias effects to several independent variables. Finally, a new means of assessing intersensory bias effects by the use of spatial separation threshold was demonstrated.

Two experiments demonstrated that when both vision and audition are providing information about temporal rates in the range of 4 to 10 Hz, audition has a much stronger influence on the bimodal percept than does vision. This case of auditory "dominance" over vision was shown to be neither the result of a difference between the sensory modalities in perceived intensity nor an artifact ofthe magnitude estimation procedure used by the subject to indicate perceived rate. It was concluded that these results provide support for a "modality appropriateness" hypothesis of the relative contribution of various sensory modalities in multimodal perception.