Processes

Crossmodal perceptual illusions such as ventriloquism, the McGurk effect, the rubber hand, and the sound-induced flash demonstrate that one sense can causally impact perceptual processing and experience that is associated with another sense. This chapter argues that such causal interactions between senses are not merely accidental. Interactions between senses are part of typical perceptual functioning. Unlike synesthesia, they reveal principled perceptual strategies for dealing with noisy, fallible sensory stimulation from multiple sources. Recalibrations resolve conflicts between senses and weight in deference to the more reliable modality. Coordination between senses thus improves the coherence and the reliability of human perceptual capacities. Therefore, some perceptual processes of the sort relevant to empirical psychology are multisensory.

Awareness

Perceptual capacities need not be reflected as such in perceptual consciousness. Thus, a subject could possess multisensory perceptual capacities while perceptual consciousness remains sense specific. For instance, a subject could detect and differentiate novel intermodal features without corresponding, irreducibly multisensory perceptual awareness. In response, this chapter argues that perceptual awareness of an object or feature sometimes is constitutively, irreducibly multisensory. In particular, it argues that the exercise of multisensory perceptual capacities can serve to make features that are not otherwise perceptible available to conscious subjects for use in thought, reasoning, and rational action. Multisensory perception thereby fixes which features are occurrently accessible to conscious perceiving subjects. The implication is that multisensory perceptual awareness cannot fully be captured in terms of sense-specific awareness.

Conclusion

This chapter recounts the arguments and conclusions reached in preceding chapters concerning the respects in which perception and perceptual consciousness involve the coordinated use of multiple senses. It provides a synopsis of considerations favoring a richly multisensory account of perceptual processes, capacities, awareness, and experience. It retraces the book’s approach to differentiating senses construed as bundles of perceptual capacities unified and distinguished by the manner in which they are exercised, and to distinguishing perception from extraperceptual cognition by means of the explanatory roles the distinction plays in empirical psychology, rational psychology, and phenomenology. It describes the theoretical consequences of multisensory perception, negative and positive, and it explains their significance. The chapter concludes with the implications and future directions for a multisensory philosophy of perception.

Senses

Multisensory phenomena have been used to challenge the distinctness of our senses. Perceptual processes interact extensively and perform joint functions, while perceptual experience is constitutively and irreducibly multisensory. This chapter presents an account of the senses and what differentiates them. According to this proposal, each sense is a family of perceptual capacities unified and distinguished by the way in which those capacities are exercised. The relevant manner is an information-gathering activity type individuated by the information it functions to extract and the medium from which it does so. Perceiving involves exercising perceptual capacities in one or more sensory manners. Thus, perceptual episodes and experiences may be typed accordingly, without appealing to their phenomenology. The key to this approach is distinguishing the task of individuating senses from that of ascribing modalities to experiences. This account rejects the independence of the senses while preserving their distinctness. It illuminates richly multisensory perception and captures why it matters.

Experience

This chapter argues that perceptual experience is richly multisensory. In particular, phenomenal consciousness is constitutively and irreducibly multisensory. The reason is that the phenomenal character of a conscious multisensory episode can include more than what is associated with each of the respective senses plus whatever accrues due to simple co-consciousness. Exercising multisensory capacities thus makes a phenomenal difference to perceptual consciousness. This difference can obtain whether or not it would enable a subject to discriminate between two otherwise equivalent experiences. It follows that the character of a perceptual episode is not exhausted by what belongs to each of the senses. Therefore, not all perceptual experience is modality specific. Coordination among the senses thus makes possible new forms of perceptual consciousness. Multisensory perception extends the varieties of experience.

Capacities

This chapter argues that typical human subjects possess distinctive multisensory perceptual capacities. Empirical evidence and theoretical considerations support the claim that perceivers are differentially sensitive to novel intermodal features, such as identity, simultaneity, motion, causality, and flavor, that could not be perceived using one sense at a time nor using several senses working merely in parallel. In light of their role in grounding cognition and guiding action, such capacities belong to perception, rather than extraperceptual cognition, for the purposes of empirical and rational psychological explanation. Therefore, multisensory perceptual capacities can serve in psychological explanations that deal with subjects and their capacities, in contrast with just subpersonal processes and mechanisms. Multisensory perception targets new features in the world. The joint use of multiple senses thus extends human perceptual capacities.

Introduction

This chapter presents the book’s thesis, its central themes, and its plan of attack. First, it describes the unisensory paradigms for investigating perception that until recently prevailed in science and in philosophy. Next, it introduces the critical respects in which perception is multisensory and explains why this is a problem for unisensory theorizing. Finally, it introduces the central questions any multisensory philosophy of perception must face, and it outlines the answers and arguments in the chapters that follow. The thesis to be defended is that coordination among the senses enhances the coherence and the reliability of human sense perception, extends its reach, and makes possible novel varieties of perceptual consciousness.