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Michael McBeath, Yoko Naylor; Blind Individuals Experience a Larger Body-Tilt Illusion than do the Sighted. Journal of Vision 2012;12(9):579. doi: 10.1167/12.9.579.
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© ARVO (1962-2015); The Authors (2016-present)
People generally exhibit a body-tilt illusion, experiencing an angle of 45° when tilted only 25°-35°. The illusion is larger when sensorially deprived, and decreases with added spatial information provided by either vision or audition. The illusion may have an ecological basis in that more tilt is experienced with body postures that detour recovery from falling (e.g. being compacted or leaning sideways). Independently, numerous studies with blind individuals document their increased non-visual sensitivity, such as superior ability in utilizing acoustic cues to judge spatial location. Such findings suggest that blind individuals likely differ from sighted in their propensity to process proprioceptive body tilt, particularly when acoustic information is available. The present study tests if blind individuals exhibit a weaker body-tilt illusion (consistent with more accurate non-visual sensory processing), or a stronger illusion (consistent with enhanced sensory resolution). We also examined if the tilt illusion systematically diminishes with increased salience of acoustic stimuli. We used an Aerotrim body-tilt machine to test 10 blind individuals and 8 sighted controls, each judging body-tilt at four levels of auditory salience, and with both eyes open versus closed. Our findings confirm that blind individuals experience a significantly larger body-tilt illusion, and that both blind and sighted populations exhibit systematic decreases in illusory tilt as auditory stimuli climb in salience through the progression of no sound, white noise, square wave, and baby crying stimuli. We also found an interaction with eyes open versus closed having no effect on blind participants, while the pattern with sighted participants replicates previous findings showing less of an illusion with eyes open. The pattern of findings is consistent with an ecological interpretation in which perceived body-tilt is systematically influenced by salience of acoustic stimuli and blind individuals, who presumably have enhanced non-visual senses, exhibit a stronger body-tilt illusion than do the sighted.
Meeting abstract presented at VSS 2012
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