DIGITIZING THE CHEMICAL SENSES 4
& Downes, 2000, 2002; Doop, Mohr, Folley, Brewer, & Park, 2006; Tortell, Luigi, Dozois,
Bouchard, Morie, & Ilan, 2007), induce hunger, and even bias our everyday behaviours
(Holland, Hendriks, & Aarts, 2005).
By contrast, stimulation of the sense of taste, retronasal olfaction,
2
and possibly also the
trigeminal sense are needed in order to deliver an authentic-tasting flavour experiences (e.g.,
Bult, de Wijk, & Hummel, 2007; Piqueras-Fiszman & Spence, 2016). Just think, for example,
about simulating the minty sensation associated with compounds such as 1-methol (the
principal flavour in mint). All three of these sensory systems are needed if one is to deliver
the characteristic minty aroma, the slightly bitter taste, and the cooling mouth-feel (involving
the tactile thermal nociceptors) associated with the experience of this particular stimulus
(Nagata, Dalton, Doolittle, & Breslin, 2005). Of course, it is not enough simply to stimulate
these senses; The relative intensity of these digital stimuli also needs to be right, as does the
time-course of increasing and decreasing sensation (see Obrist, Comber, Subramanian,
Piqueras-Fiszman, Velasco, & Spence, 2014; Stuckey, 2012), if one wants to simulate a
genuinely-compelling (i.e., authentic) minty sensation.
Taste (strictly-speaking, gustation) and flavour (the latter referring to the combined input of
gustatory, olfactory, and possibly also trigeminal stimulation) are undoubtedly complex
concepts to try and disentangle, both at the theoretical and at the empirical levels (see Spence,
Smith, & Auvray, 2015, for a review). Matters are made more confusing by the existence of
phenomenon such as oral referral (of odours to the oral cavity; see Spence, 2016a, for a
review), and the fact that different terms are sometimes used in different languages to refer to
these two percepts (e.g., Rozin, 1982; Spence, 2017a). Here it is perhaps helpful to bear in
mind that stimulation of the taste-buds on the human tongue may only give rise to the
sensation of sweet, bitter, salty, sour, and umami.
3
Everything else that we enjoy while tasting
– the meaty, the fruity, the floral, the herbaceous, and the roasted etc. – are all delivered by
the sense of smell instead.
4
That is, by volatile molecules hitting the olfactory receptors
embedded in the nasal mucosa. It is one of the tricks of the mind that so much of this
information, transduced by the olfactory receptors in the nose is referred to the mouth, giving
us all the illusion that we are tasting (this is what it is referred to as ‘oral referral’). So, when
talking about the digitization of the chemical senses, one needs to keep taste distinct from
tasting (the latter normally used to refer to the flavour perceived; see Spence et al., 2015). It
is worth bearing in mind that it has widely been estimated that 75-95% of what we think we
taste really reflects information delivered by the sense of smell (see Spence, 2015a, for a
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2
Retronasal olfaction is based on the volatile-rich air that is pulsed out from the back of the nose whenever we
swallow (e.g., Bojanowski & Hummel, 2012).
3
That said, a growing number of researchers now believe that oleogustus, or fatty acid, should be considered as
the sixth taste (e.g., Keast & Costanzo, 2015; Running, Craig, & Mattes, 2015). Then there is kokumi, not to
mention the recently-discovered taste for glucose oligomers (Lapis, Penner, & Lim, 2016). However, while we
may well be able to discriminate these stimuli in taste tests, it is not so clear that they are all necessarily
associated with a clearly identifiable taste percept.
4
It is currently unclear whether the metallic sensation one sometimes gets is a taste, a retronasal aroma, or a
flavour (see Skinner, Lim, Tarrega, Ford, Linforth, & Hort, in press; Spence et al., 2015).