DUPLEXITY THEORY OF TASTE.

When two different taste stimuli are presented, one to the left and the other to the right side of the tongue, they may add together to a sensation in the middle of the tongue, or they may stay separated. This phenomenon can be used to show that the four primary taste sensations seem to form two well-differentiated groups. Warm and cold stimuli act similarly to the four primary taste stimuli, thus separating the sensations on the tongue into two groups: bitter, warm, sweet; and sour, cold, salty.