Gustatory cross adaptation: Sourness and bitterness

In five experiments, Sa were presented with a variety of sour and bitter compounds after the tongue was rinsed with distilled H₂0, QHCl, urea, or citric acid. All the acids tested were significantly less sour following adaptation to citric acid than after adaptation to distilled H₂O. The taste of these acids was not affected by rinsing the tongue with QHCl or urea. QHCl adaptation markedly reduced the bitterness of some compounds, while having little effect on others, including urea and citric acid. Both urea and citric acid had smaller but reliable effects on the bitterness of QHCI. These apparently incompatible results do not seem to be the result of a simple verbal confusion between sourness and bitterness. Some compounds were not affected by any of the adapting conditions. The coding mechanisms for the sourness of acids appears to be relatively simple, while that for bitterness is more complex.