Abstract
Though human sensations, such as the senses of hearing, sight, etc., are independent each other, the interference between two of them is sometimes observed, and is called cross-modal perception[1]. Hitherto we studied unimodal perception of visual sensation[2] and auditory sensation[3] respectively by differential geometry[4]. We interpreted the parallel alley and the distance alley as two geodesics under different conditions in a visual space, and depicted the trace of continuous vowel speech as the geodesics through phonemes on a vowel plane. In this work, cross-modal perception is similarly treated from the standpoint of non-Riemannian geometry, where each axis of a cross-modal sensory space represents unimodal sensation. The geometry allows us to treat asymmetric metric tensor and hence a non-Euclidean concept of anholonomic objects, representing unidirectional property of cross-modal perception. The McGurk effect in audiovisual perception[5] and ‘rubber hand’ illusion in visual tactile perception[6] can afford experimental evidence of torsion tensor. The origin of ‘bouncing balls’ illusion[7] is discussed from the standpoint of an audiovisual cross-modal sensory space in a qualitative manner.