Taste Adaptation

Although the saliva that constantly bathes our tongue contains a number of taste stimuli, we ordinarily find it quite tasteless. However, if you were to rinse your tongue with water for a minute or so, you would find your own saliva to have a distinctly salty taste. And if you rinsed the tongue with a salt solution only somewhat saltier than your saliva, pure water would then taste distinctly sour-bitter. Thus, the tongue is constantly adapts to the stimuli that surround it and responds to changes from the adapting level. The range over which adaptation is complete is at least two orders of magnitude, or more than 100 to 1.

As in all the senses, adaptation in taste has many important functions. Most obvious is the role of adaptation in tuning out steady stimulation, as in the previous example. But this is only one of a number of functions of adaptation found in the senses in general. The effects discussed here tend to have their analogs in the other senses.

After adapting to a given concentration of salt, the tongue is better able to detect changes in concentration near the adapting level than it would have been without adaptation. In other words, the difference threshold is smaller near the adapting concentration. In addition, the tongue responds more to increases in concentration than it did before adaptation. Thus, the rate of increase in sensation with increasing concentration becomes steeper. So after adaptation, the threshold concentration required to produce a sensation is greater than before, but the sensations caused by stronger concentrations are less affected.

These two effects illustrate how adaptation acts as a sort of range-finding mechanism that adjusts its sensitivity up or down in order to keep the system as responsive as possible. This is similar to the way a camera adjusts to changing light levels. Thus, it is misleading to think of adaptation primarily as a loss of sensation. The sensation caused by a given stimulus does decrease with adaptation, but the system is more sensitive to changes in stimulation near the adapting concentration than it was before adaptation. This entry describes adaptation as temporal sensitivity, water taste, adaptation and the basic tastes, importance of method of stimulus presentation, and the relation between adaptation and habituation.