Olfactory-induced synesthesias: A review and model.

Abstract

Recent reviews of synesthesia concentrate upon rare neurodevelopmental examples and exclude common olfactory-induced experiences with which they may profitably be compared. Like the neurodevelopmental synesthesias, odor-induced experiences involve different sensory modalities; are reliable, asymmetric (concurrents cannot induce), and automatic; and the inducer-concurrent relationship is learnt. Unlike neurodevelopmental synesthesias, these experiences are universal and their synesthetic nature goes unrecognized. Olfaction's ability to universally induce concurrents may result from its unique neuroanatomy, affording dual access to neocortex. We propose that concurrents arise here via a twofold process: by direct neocortical activation, which recovers a configural memory, and by attribution of this memory to the olfactory modality by thalamic attentional processes. The implications of this for other forms of synesthesia are then examined.

A deafening flash! Visual interference of auditory signal detection

“…Similar reasoning might explain why rare shape-taste correspondences are classified as synaesthetic, but not taste-smell associations (e.g. the 'sweet' smell of chocolate (Stevenson & Tomiczek, 2007;van Campen, 2008) which naturally belong together and are thus highly predictable. This perspective of ignored or discounted concurrents predicts that awareness of visuallyevoked sounds might be promoted in some individuals if attention is drawn to them under verifiably silent conditions.…”

Crossmodal correspondences between odors and contingent features: odors, musical notes, and geometrical shapes

“…A benefit of the present account comes, then, from proposing that attributions of "sweetness" (Stevenson & Boakes, 2004), pitch elevation (Belkin et al, 1997;Crisinel & Spence, 2012b), hue (Gilbert, Martin, & Kemp, 1996), brightness (Schiller, 1935), or shape (Hanson-Vaux et al, 2013; can be explained in terms of perceptual processes grounded in exposure and structural determinants, instead of being divided between "synesthetic" connections, on the one hand (Stevenson & Tomiczek, 2007), and conceptual or metaphorical transfers, on the other. It also crucially expands consideration of the crossmodal associations elicited by olfactory cues beyond the idiosyncratic evocations studied as the "Proust phenomenon" (e.g., Chu & Downes, 2002;Willander & Larsson, 2006.…”

“…The final section concludes with two arguments related to seeking a better understanding of the crossmodal correspondences holding between contingent features, such as those holding between smells and auditory or shape features: First, researchers should resist the idea that the associations are merely anecdotal, but rather should subject them to systematic investigation (see also Stevenson et al, 2012). Second, we propose an alternative framework to investigate the most surprising cases of crossmodal associations, one that contrasts with their being seen as either synesthetic connections (an interpretation that was suggested for smelltaste associations by Stevenson & Tomiczek, 2007, and is easily extended to crossmodal associations between smell and musical notes) or merely grounded in episodic memories (as has been proposed to explain "Proustian" associations between odors and visual images; see Chu & Downes, 2002;Willander & Larsson, 2006.…”

As bitter as a trombone: Synesthetic correspondences in nonsynesthetes between tastes/flavors and musical notes

“…We live in a multisensory world, and our brains constantly combine information from different sensory modalities in order to make sense of our environment (see Calvert, Spence, & Stein, 2004). The senses of taste and smell are so tightly combined in the evaluation of flavor that it is sometimes considered a form of synesthesia that is common to us all (Auvray & Spence, 2008;Small & Prescott, 2005;Stevenson & Tomiczek, 2007; see also Djordjevic, Zatorre, & Jones-Gotman, 2004). Moreover, the evaluation of the sweetness (i.e., a gustatory property) of a novel odor can be modified simply by pairing it during training with a sweet taste (Stevenson, Boakes, & Prescott, 1998).…”