Human Olfaction, Crossmodal Perception, and Consciousness

When philosophers attempt to provide a theory of perception they usually focus exclusively on vision, assuming, without argument, that it can serve as a model for perception in general, extendible, with minor modifications, to all other senses. This is a hopeless strategy and Andreas Keller’s monograph is a useful corrective to it. The concluding chapter, Comparing Olfaction and Vision, would be an excellent self-standing essay. In fact, it is Keller’s desire to distance himself from visuocentrism in the philosophy, psychology, and neuroscience of perception that led him to pursue a second doctorate on philosophy and write this monograph on olfactory perception. As Keller reminds us, “visual perception in humans is fundamentally different from human olfactory perception” (p.193). Olfaction does not maintain a permanent olfactory scene in the way vision sustains our view of our immediate surroundings. There is no agreed way to organize perceptual smell space or identify its fundamental categories as there is for color or sound space. Olfaction has close ties to the emotions and only weak links to language; odors are difficult to name. The grouping of odors in olfactory perception reflects the behavioral needs and responses of individuals, not physical similarities among the stimuli. These distinguishing features give olfaction a different function and character from vision; in particular, olfactory perception does not involve, for Keller, the perception of objects. A key reason for this conclusion is Keller’s conviction that the perceptual space of olfaction is not spatially or temporally structured. The arguments for this claim come in Chapter 3 where he discounts different attempts to establish candidates for olfactory objects. His strategy is to consider criteria for objecthood in a perceived scene and to see whether these criteria are met in the case of smells. These include a distinction between figure and ground in perception, and the so-called Many Properties problem of deciding, for any perceived scene, which properties go with which objects; an instance of the binding problem. Keller works through cases and finds them wanting. Smells may be distinct to the perceiver, the smell of baked goods and fresh coffee, say, but which is the figure and which is the ground? We seem unable to provide an answer. The trouble with this strategy is that is takes the figure-ground distinction in olfaction to be modeled on the visual case, and Keller even tells us at one point: