Relative hedonic value modulates anticipatory contrast.

Intake of an initial substance (e.g., 0.15% saccharin) is suppressed when the presentation of this substance precedes the availability of a preferred solution (e.g., 32% sucrose) in brief daily pairings. The present experiments show that degree of this anticipatory contrast effect is related to the relative hedonic value of the substances paired each day. When the initial substance has low hedonic value relative to the second substance (e.g., water or empty tube paired with 32% sucrose), then a facilitation effect rather than contrast occurs. As the hedonic value of the initial substance increases (0.0015% saccharin, 0.5% sucrose, 0.015% saccharin, 1% sucrose, 2% sucrose, 0.15% saccharin), facilitation is replaced by contrast, which develops sooner and becomes larger the greater the hedonic value of the initial substance. The serotonin antagonist cyproheptadine increased absolute lick frequencies, but did not alter contrast. The serotonin1A agonist buspirone tended to decrease absolute lick frequencies, but did not alter contrast. The occurrence of contrast is discussed in terms of response competition, inhibition, and devaluation of the initial substance.