Blackwell Handbook of Perception

Edited by E. Bruce Goldstein

Blackwell Publishers, 788pp, £85.00

ISBN 0 631 20683 3

Published January 2001

Perception is a major research focus in the disciplines of both psychology and physiology. The psychological approach to the study of perception is to characterise the relationship between a stimulus and the perceptual response it elicits; an enterprise termed "psychophysics". The physiological approach is to document the activity of brain cells (neurons) in response to sensory stimulation. Running through this collection of chapters is the theme that "cross-talk" between the psychophysical and physiological approaches has facilitated both disciplines' progress in understanding perception. Ultimately, to understand perception we must understand the relationship between physiological processes and their perceptual correlates. To do so will necessarily require extensive communication between disciplines, principally, Goldstein argues in the introductory chapter, with psychophysics guiding physiological research.

Nowhere in the book is the value of such inter-disciplinary communication better exemplified than in Gordon and Abramov's chapter on colour vision. The point that the sensation of colour derives entirely from processing by the nervous system is eloquently made with a quotation from Newton's Opticks: "For the rays to speak properly are not coloured. In them there is nothing else than a certain power and disposition to stir up a sensation of this or that Colour". Colour vision begins with the absorption of light by cones in the retina. The range of wavelengths absorbed by a given cone depends on the absorption spectrum of the photopigment it contains. In normal "trichromatic" human observers there are three classes of cone photoreceptor with peak sensitivities in the short-, medium- and long-wavelength ranges of the visible spectrum. While Thomas Young inferred that normal human vision is trichromatic nearly 200 years ago on the basis of psychophysical observations, it was over 150 years before the existence of three classes of cone photoreceptors in the human retina was confirmed physiologically. The wavelength of incident light is coded in the pattern of activity across these three cone classes. However, there is no simple correspondence between stimulus wavelength and perceived colour. Signals from the three cone classes are recombined in spectrally opponent retinal mechanisms. This physiological opponency was also predicted from psychophysical observation, this time by Edward Hering in 1920. Finally, visual signals from the retina are relayed deep into the brain where stimulus wavelength is translated into information about the reflectance properties ("colour") of objects in the visual scene by effectively discounting the spectral composition of the light illuminating the scene. While the phenomenon of colour constancy has been much studied by psychophysicists, understanding of the underlying cortical mechanisms is still far from complete.

Approximately half of the Blackwell Handbook of Perception is dedicated to vision, with chapters concentrating on the visual perception of space and objects by observers with normal and damaged brains, perception of and attention to visual events, and the contentious proposal that there are separate visual systems underlying action and perception. However, vision is but one of five senses. Five of the twenty-three chapters deal exclusively with auditory perception. Beginning with a description of basic auditory processing, this section takes the reader through the way in which sounds are localized and properties such as pitch and timbre are perceived, ending with chapters on the perception of music and recognition of the spoken word. One chapter is also devoted to each of the other three senses: smell, taste and touch.

The modular structure of the book, dividing perception into five senses and sub-dividing these senses into modalities such as colour vision and motion perception, reflects the highly modular architecture of our sensory systems. From the modular chapters, bound together, emerges a book whose significance well exceeds the sum of its parts. From patterns of neural activity distributed across our sensory systems emerges the unity of perceptual experience familiar to us all. However, in the case of the brain, it is far from clear how such unity arises. For example, if one area of the brain processes the motion of a visual stimulus while another area deals with its colour then how is it that the properties of motion and colour become associated with the same object? The question of how different attributes of the same object are bound together perceptually is known, aptly enough, as the Binding Problem. In his introduction, Goldstein refers to the Binding Problem with some understatement as "one of the more challenging problems in object recognition". In fact, the Binding Problem is one of the central questions of cognitive psychology. While there is, as yet, no adequate answer to the Binding Problem, the final two chapters of the book provide an excellent overview of recent progress in understanding the nature of inter-sensory and intra-sensory integration, respectively. The chapter by Stein and colleagues on neural mechanisms of cross-modal synthesis focuses on the role of a particular midbrain structure, the superior colliculus, in mediating interactions among the senses. The chapter by Nakayama concentrates on the nature of functional modules such as the face recognition system, arguing that the study of modular aspects of perception might lead to general principles underlying modules in other more cognitive domains.

The Blackwell Handbook of Perception is an excellent reference for researchers in perception and cognition. Each chapter begins with a page of contents, making it is easy to find relevant material quickly, and concludes with a list of suggested readings and additional topics. It is suitable for graduate students interested in perceptual psychology and possibly also advanced undergraduates.