Multi-Modal Food Perception

Think about food - when we eat food, from healthy vegetables to delicious cupcakes, we are not just engaging our sense of taste. We see the food, feel its texture in our hands and in our mouths, we smell it, and, of course, we taste it. A 2005 review paper by Verhagen and Engelen discusses the interactions between our senses when we eat, using evidence at the neural, perceptual, and behavioral levels. They describe the experience of eating thus:

   Taking in a piece of food will allow the rapid recognition of its size, shape, and temperature. When food is 
   chewed, this leads to the breakdown of its matrix which, in turn, releases odorants, tastants, and chemesthetic 
   substances; at the same time the moving tongue and palate can sample further the food's texture and temperature. 
   Breaking down of the food's matrix can concomitantly lead to vibrotactile and bone-conducted auditory sensations 
   (617).

Taste-smell Interactions

As Verhagen and Engelen mention, taste and smell hardly ever appear in isolation from one another when it comes to food, and there is some evidence that the olfactory and gustatory systems may, to a degree, work in tandem. According to Verhagen and Engelen, subthreshold taste and smell may be cross-modally integrated centrally - the anatomical basis for this is unknown, but may involve bimodal taste-smell neurons in the orbitofrontal cortex. As the authors also discuss, studies have shown that taste can enhance reported odour intensity, and vice versa. Additionally, people with sense-of-smell disorders also commonly have issues regarding taste. The link between taste and smell is very strong - some researchers even refer to this connection as a type of synaesthesia. cupcake.jpg

Taste-touch Interactions

Evidence presented in Verhagen and Engelen also demonstrates a link between taste and touch. Several studies mentioned in the paper showed that taste (sweetness versus citric acid) had an effect on reported viscosity ratings of food. Conversely, another study presented in this paper demonstrated an effect of taste on touch - taste stimuli were 'painted' onto parts of the tongue with taste receptors and parts of the tongue without taste receptors, resulting in a perception of taste that followed the tactile stimulus across all parts (635).

Other Taste Interactions

Temperature also has an effect on taste - as the temperature of food approaches that of the tongue, its rated taste intensity increases. In another study described by Verhagen and Engelen, Cruz and Green (2000) demonstrated that cooling or warming small areas of the tongue can result in weak taste sensations.

Taste can also affect tongue irritation - when foods containing piperine and capsaicin are consumed, sucrose, citric acid, or water can reduce the burning sensation experienced. The next time you eat spicy food, remember this! Conversely, taste irritants, like capsaicin, can affect taste, reducing the perceived intensity of sweetness.

Vision and taste are also somewhat inter-related when it comes to food perception, particularly when it comes to colour. In studies in which colour was added to water solutions, red was shown to increase perceived sweetness, although evidence for other colour-taste interactions is unclear.

Other Interactions

Verhagen and Engelen describe a number of studies showing interactions between smell and the other senses. A study by de Wijk et al. demonstrated that subjects' reports of the texture (creaminess, melting, and thickness) of an ingested sample of custard was affected by smell. Other studies described by Verhagen and Engelen showed that subjects were influenced by the texture of a sample when reporting the intensity of its odor.

Smell and irritation have also been shown to be related. In a study by Cain and Murphy (1980), researchers were able to suppress irritation in subjects using odour, and vice versa.

Effects on smell by vision have been reported as well, with studies showing that subjects are more likely to rate odours as more intense if colour intensity is also high. This effect can particularly be seen when it comes to odourless substances - subjects are more likely to rate an odourless substance as having an odour if it is coloured than if it is colourless.

Effects of temperature on smell and vice versa are also discussed by Verhagen and Engelen, although they say that this may in fact be due to the effects of temperature on odorous compounds, rather than any binding of the senses.

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