A further consequence of such odour/taste co-occurrence
is that odours that smell sweet (or salty, sour, bitter) are
able to modify those taste qualities when experienced
together as a flavour. Thus, a strawberry flavour (odour
plus sweet taste) is perceived as sweeter than the sweet
taste alone, despite the fact that the odour alone in
solution istasteless. Such odour-induced taste enhancement
has been obtained in many differentsettings using
diverse odourants and tastants [11,20]. One model
developed to explain this process proposes that each
experience of an odour always invokes a search of
memory for prior encounters with that odour. If the
initial experience of the odour was being paired with a
taste, a cross-modal stimulus — that is, a flavour — is
encoded in memory. Subsequently sniffing the odour
alone will evoke the most similar odour memory — the
flavour — that will include both the odour and the taste
component. Thus, for example, sniffing caramel odour
activates memory of caramel flavour, which includes a
sweet taste component. This results either in perceptions
of smelled taste properties such as sweetness or, in
the case of a mixture, a perceptual combination of the
odour memory with the physically present taste in
solution [21]. Although this happens automatically, to
a large extent we are conscious of the encoding of odour
taste properties. Hence, when untrained study participants
are asked to describe the quality of sniffed odours
the term ‘sweetness’ is used at least as often asthe actual
odour name, when that odour has been previously
paired with a sweet taste.