An Auditory Illusion Induced By Unambiguous Visual Stimuli. Elizabeth Yockey, Timothy Zeedyk, Jonathan Dereszynski, Department of Psychology, Alma College, Alma, Michigan 48801 Recent studies in the field of stimulus research have suggested that information from one sense can qualitatively affect the perception of information from another sense. A study done by L. Shams (et al., 2000) reported that a visual illusion was created by altering a near simultaneous auditory input with respect to a visual counterpart. In essence, a series of beeps after the tachistoscopic presentation of a white dot caused the illusion of multiple dots. A similar experiment was constructed by B.E. Stein (et al., 1996) which attempted to alter the intensity of a visual stimulus by an auditory stimulus. The subjects were presented with a LED flash and a simultaneous, broad-band, auditory stimulus. The auditory stimulus was reported to have increased the intensity of the visual stimulus at the lower visual intensity flashes. A crosslinking between auditory and visual sensory processes was again demonstrated in a study done by J.O. Spencer (et al., 1973). The study attempted to discern the ability to respond to auditory nonsense in the presence of visual images of varying complexity. The study demonstrated a slower response time with images of increased complexity. This suggests that the two sense may use the same Òprocessing powerÓ or they may be interlinked in some other way. In our study, we attempt to discern whether the reverse is true between visual and auditory stimuli. In many of these types of studies, the auditory stimulus affects the intensity, or other characteristics, of the visual stimulus. We attempt to discover if the visual stimulus can in some way alter the intensity of the auditory stimulus. Materials and Methods Population- Our population consisted of 21 Alma College students between the ages of 19 and 21. There were relatively equal numbers of male and female students. Apparatus-For this study we used a Macintosh computer. We used a program constructed by Dr. Walter Beagley that displayed a series of brief flashes on the screen in synchrony with a tone. First there was a single tone, then a single tone with the flashes, then another single tone. There were two variants to this stimulus. The first was one in which the tones were all of the same duration. The second was one in which the middle tone is shorter than the first or the third. There was a sequence of ten sets of three tones each. The stimuli were in an order which was unknown to the subjects. Testing-The subjects were presented with the test twice. Once without the computer monitor on so that they could observe the tones without the visual effect. The computer monitor was then turned on so that the visual effect could be observed and the test was then repeated. Subjects were then asked to identify if each series of tones sounded the same or different. Results were then recorded by hand and then transcribed to a Microsoft Excel spreadsheet. Statistical Analysis-Results were compiled into a Microsoft Excel spreadsheet. Means were taken for results indicating the tones were the same. Results and Conclusions Results-The effect of the illusion was a minor one. As our table shows, subjects presented equal tones without a flash performed slightly better than those exposed to equal tones with a flash. This was expected as the illusion was intended to distort the sound. Subjects presented different tones with a flash performed slightly better than those presented a tone without a flash. This is unexpected, however, many subjects reported that the flashes caused a prolonging of the tone, or it appeared to Òstretch out the soundÓ. Further testing would be required to verify this. Conclusions-We found the illusion to have a somewhat weak effect. If this experiment were repeated, we would use a slightly more discriminable tone difference. We would also investigate our subjects more thoroughly and avoid those with musical backgrounds. We found subjects with musical experience nearly immune to the effects of the illusion. We would also attempt to insure accurate test conditions as a few of the subjects did not comply with the instructions given before the testing. Literature Cited Shams, L., Kamitani, Y., and S. Shimojo. 2000. What you see is what you hear. Nature. 408(6814): 788. Spencer, J.O. 1973. Suppression of perceptual organization in the auditory mode by the presence of visual stimuli. Bulletin of the Psychonomic Society. 1(1-A): 31-32. Stein, B.E., London, N., Wilkinson, L.K., and D.D. Price. 1996. Enhancement of perceived visual intensity by auditory stimuli: A psychophysical analysis. Journal of Cognitive Neuroscience. 8(6): 497-506.