Why does the sense of smell vanish in the mouth? Testing predictions from two accounts

Headnote

Abstract When participants perceive flavor they do not recognise the role of smell. We examined two possible accounts of why: (1) a common attentional channel activated by taste; and (2) prior learning between taste and smell. Participants were asked to snifffood-related odors with a fluid in their mouth and profile each odor after expectorating. This process was later repeated for each odor, with some odors experienced with water on both occasions, and others with water on one occasion and sucrose (weak or strong) on the other. We investigated how reliable these odor profiles were and whether they were influenced by prior odor-taste learning (indexed by odor sweetness). For non-sweet smells, the presence of a tastant significantly improved profile reliability relative to water in the mouth. For sweet smells, tastant had no effect, which we suggest represents a cancelling out of the beneficial effects of the common attentional channel by the detrimental effects of prior learning. Thus, both mechanisms may contribute to masking the modal identity of smell thereby contributing to flavor binding.

Keywords Taste . Smell . Flavor . Multisensory integration

Introduction

Multisensory integration may occur when stimuli share a common spatial location and time-course (e.g., Stein,Wallace & Stanford, 2001). One example of this is flavor perception. Taste, olfactory, and somatosensory information arising from a common location in the mouth, and occurring over a similar time course, gives rise to flavor (e.g., Small & Prescott, 2005). The precise mechanics of flavor binding are a matter of debate, partly at least because some of its characteristics are unusual (Stevenson, 2014). In particular, olfaction has two modes of perception but only one set of receptors (Rozin, 1982). In one mode, odorants are perceived as smells arising in the environment when they are sniffed at the nose (orthonasal perception). In the other, odorants in food released by chewing stimulate the olfactory receptors via the internal nares (retronasal perception) and are described as "taste" or flavor.

What makes the distinction between these two modes of perception unusual is not the shiftof perceived location (nose/mouth), of which there are other examples (e.g., ventriloquism; Bertelson & Radeau, 1981), but the change in modality awareness.While the ventriloquist's voice may seem to arise from another source, it is still perceived as a...