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Shared content across perceptual modalities: lessons from cross-modal illusions.

Author(s): Casey O'Callaghan

Journal: Electroneurobiología
ISSN 0328-0446

Volume: 14;
Issue: 2;
Start page: 211;
Date: 2006;
Original page

Keywords: perception | mentation | illusion | cross-modal illusionsl sentience | visual experience | noemata | noema | noesis | consciousness studies | philosophy of mind | shared content across perceptual modalities

Each perceptual modality cannot fully be understood in isolation from the others. The recently discovered sound-induced flash illusion is a visual illusion induced by sound (Shams et al. 2000, 2002). A single flash paired with multiple beeps is perceived as multiple flashes. The illusion is characterized by its discoverers as being induced by audition as a result of "cross-modal perceptual interactions" (2002:147). Alva Noë has recently challenged on independent grounds what he calls the "snapshot conception" of visual experience according to which perception presents discrete snapshot-like contents that represent a scene "in sharp focus and uniform detail from the center out to the periphery" (Noë 2004, ch. 2). On the basis of a discussion of cross- and inter-modal perceptual effects, I argue in this paper that what I dub the "composite snapshot" conception of overall perceptual experience fails. Cross-modal and inter-modal illusions, including the sound-induced flash illusion and the more familiar ventriloquist illusion (in which vision influences sound localization) suggest that the influence of one modality upon the phenomenological and perceptual content of another modality requires for its explanation appeal to a dimension of shared content across perceptual modalities. The cross-modal illusions thus demonstrate that a visuo-centric focus in theorizing about perception and perceptual content threatens to blind us to the nature and character of perceptual experience. Such effects indicate that individual modalities cannot fully be understood in isolation from the others – even vision and visual content are illuminated by considering the non-visual modalities. Abandoning both the visuo-centric focus in theorizing about perceptual experience and the composite snapshot conception of experience also contributes to resolving puzzles about the other modalities. For instance, auditory perception plays a role in situating subjects in a world of objects and events. Auditory perception, that is, reveals not only a world of sounds but also furnishes information about the things and happenings that generate those sounds. How could audition, whose proper objects are sounds, include object-involving content? Appeal to a shared dimension of content among perceptual modalities makes this question tractable. Common content among modalities, appeal to which is required to explain cross-modal effects, could ground an explanation for how audition might furnish genuinely perceptual awareness of objects and happenings and not mere inferential or otherwise non-perceptual awareness. In short, attention to cross- and inter-modal effects and illusions enhances our understanding of the phenomenological and perceptual contents of experience by encouraging us to move beyond characterizing perceptual content as a composite of modality-specific contents. (Article in English).
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