Abstract
Casey O’Callaghan tackles a fundamental aspect of the interface between our brain and the world. He explores the multisensory nature of perception through the lens of theoretical and philosophical frameworks. The book mounts an incremental and compelling argument against theories that define perceptual consciousness as a collection of distinct, individual sensory experiences. O’Callaghan contends that the sense-by-sense approach is incomplete and that the sum of individual senses does not yield a complete account of sensory perception. He argues that sensory interactions are key to reliability of perception and, contrary to parallel unisensory perception, they can enrich perceptual consciousness over time. In this view, multisensory interactions are vital to reveal more of the world, and they could provide practical, epistemic, and aesthetic benefits. O’Callaghan goes on further with how perceptions formed by stimulations from the environment can lead to beliefs or trigger thoughts.
To build a case, the book begins by examining perceptual illusions when one sense can trigger illusions associated with other senses (chapter 2). It argues that sensory interactions generally conform to principles that enable us to get things right. In typical conditions, these processes compensate for ambiguity or conflict among sensory inputs by weighting more in favor of the more reliable modality. This makes sense in dealing with noisy, fallible sensory information that comes from multiple sources. The same processes, however, can produce illusions in certain circumstances in which sensory interactions through the same principles can become misleading. O’Callaghan then argues that perceptual systems hold capacities that are accessible only through coordinated use of multiple senses (chapter 3), and such multisensory capacities also apply to perceptual awareness and phenomenality—a process which determines what it is like to undergo a certain perceptual experience (chapters 4 & 5). On this ground, a key question is raised about what constitutes a sense (chapter 6). He goes on to propose that each sense is a collection of perceptual capacities, and what unites or distinguishes them is a distinctive manner by which those capacities are exercised—take for example the capacity to perceive shape which can be exercised through different modalities such as vision or touch. Throughout the chapters, the ground for skepticism from proponents of unisensory approaches are considered as well, and the rebuttal arguments are laid out in support of multisensory perceptual experiences.
Overall, the book is ripe with deductive reasonings and rational arguments that account for multisensory perceptual capacities in humans. At times, a familiar example or a typical scenario is described to aid readers navigate through complex concepts. For instance, in a place where the concept of sensory interaction and reliability of perception are discussed (page 42), you are asked to imagine sitting in a well-lit room where you can discern the location of someone talking by hearing and by sight. In cases like this, visual information can improve hearing and enhance spatial localization through sensory interaction. If you just trusted hearing or if visual and auditory information did not interact, adding vision would not make a difference in how you perceive sound location. Such tangible scenarios can help general-interest readers and would be valuable if used in more places throughout the book. It could be especially helpful where novel facets of perception are discussed in technical terms. In some parts, citations are included only in passing, which makes it difficult for non-expert readers to follow and understand their relevance. It was also surprising to see some of the great examples of multisensory processing such as spatial orientation and perception of gravity mentioned only in a footnote (page 74) or briefly in the epilogue (page 197), and not see them in support of crossmodal sensory interactions in more places throughout the book. I found the general format of the chapters with a synopsis or concluding segment at the end very helpful to effectively recount the key points raised. In addition, the final conclusions were clearly summed up in the last chapter (page 180). All in all, I think the book is successful in providing a sensible narrative that can dissect and describe boundaries between concepts related to multisensory attributes, perception, and cognition. It provides valuable perspectives to form hypotheses about brain functions related to sensory processing or integration and offers a structure to examine them accordingly. Anyone with interest in the study of sensory processing and perception would enjoy reading this book.
