Sensory interaction: the joint effects of visual and auditory stimulation on critical flicker fusion frequency
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Abstract
The purpose of the present study was to formulate and test deductions from a theory of intersensory effects (stimulation of one sense modality modifying the sensitivity of another sense modality). A model of "mutually recruitable neurones" (MRN), a quasi-neurological construct advanced in recent research on intersensory effects, was employed to generate hypotheses concerning the magnitude and direction of such effects upon critical flicker fusion frequency (CFF) as a joint function of intensity of illumination and intensity of tone.
A review of the literature pertaining to sensory interaction suggested that among the factors which may determine the magnitude and direction of intersensory effects are the intensities of the stimuli applied jointly to two sensory systems.
The model of MRN was used to develop certain assumd relationships which were stated in terms of postulates. The experimental hypotheses, derived from these postulates, were applied to vision and audition and were stated as follows:
General Hypothesis:
Visual sensitivity is a joint function of visual stimulation and concurrent auditory stimulation.
Specific Hypotheses:
A) Facilitation and inhibition of visual sensitivity bear a diphasic relationship to the intensity of auditory stimulation. Visual sensitivity will increase and then decrease as a function of increasing intensity of auditory stimulation.
B) Facilitation of visual sensitivity brought about by auditory stimulation is a positive function of intensity of visual stimulation.
C) Inhibition of visual sensitivity brought about by auditory stimulation is a negative function of intensity of visual stimulation.
The data consisted of repeated thresholds obtained from two subjects. The measure of visual sensitivity was CFF. Intensity of visual stimulation consisted of three levels of brightness of the flashing light, while auditory stimulation consisted of twelve intensities of a 1550 cycle per second tone binaurally delivered. For each light intensity ascending and descending CFF's were measured continuously for a thirty second period prior to the onset of each tone and for a thirty second period immediately following the maximization of each of the tones.
Initially, the general hypothesis was supported only in the case of the second subject. Although intersensory effects were shown to depend on illumination in the case of both subjects, and both illumination and tone in the case of the second subject, CFF's of the first subject showed only facilitation in varying degrees across the tonal intensities. However, when further experimentation with this subject was carried out employing tones of greater intensity, inhibition of CFF was obtained, the heretofore lacking diphasic relationship could be shown, and inferentially the general hypothesis supported in the case of this subject as well as the second.
The absence of significant sensory interaction at a low level of illumination observed under the conditions of the present experiment was discussed in terms of the postulates. A post hoc scheme was offered which proposed that rather than increasing the magnitude of facilitation only, the effect of increasing illumination might be to increase the magnitude of all intersensory effects brought about by tone, whether facilitative or inhibitory. Conversely, the effect of decreasing illumination might be to decrease the magnitude of all intersensory effects. Unlike any of the other theories reviewed, the model of MRN allowed the statenent of an alternate postulate which would be consistent with the data obtained.
Implications of the experiment were discussed. In general the results were consistent with the main body of intersensory literature. The suggestion was made that while the form of the theoretical diphasic curve describing the relationship between a sensory response and stimulation to more than one sense organ may be of a general nature, applying to all individuals, the results of the present study suggest that considerable additional research may be necessary in order to specify whether a given individual must supply the parameters for these functions. Implications of the experiment were discussed. In general the results were consistent with the main body of intersensory literature. The suggestion was made that while the form of the theoretical diphasic curve describing the relationship between a sensory response and stimulation to more than one sense organ may be of a general nature, applying to all individuals, the results of the present study suggest that considerable additional research may be necessary in order to specify whether a given individual must supply the parameters for these functions.
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Thesis (Ph.D.)--Boston University
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