An audiovisual stimulus was made contingent upon the rat's licking at the water spout, thus making it analogous with a gustatory stimulus. When the audiovisual stimulus and the gustatory stimulus were paired with electric shock the avoidance reactions transferred to the audiovisual stimulus, but not the gustatory stimulus. Conversely, when both stimuli were paired with toxin or x-ray the avoidance reactions transferred to the gustatory stimulus, but not the audiovisual stimulus. Apparently stimuli are selected as cues dependent upon the nature of the subsequent reinforcer.A great deal of evidence stemming from diverse sources suggests an inadequacy in the usual formulations concerning reinforcement. Barnett (1963) has described the "bait-shy" behavior of wild rats which have survived a poisoning attempt. These animals utilizing olfactory and gustatory cues. avoid the poison bait which previously made them ill. However. there is no evidence that they a void the "place" of the poisoning.In a recent volume (Haley & Snyder. 1964) several authors have discussed studies in which ionizing radiations were employed as a noxious stimulus to produce avoidance reactions in animals. Ionizing radiation like many poisons produces gastrointestinal disturbances and nausea. Strong aversions are readily established in animals when distinctively flavored fluids are conditionally paired with x-rays. Subsequently. the gustatory stimulus will depress fluid intake without radiation. In contrast. a distinctive environmental complex of auditory. visual, and tactual stimUli does not inhibit drinking even when the compound stimulus is associated with the identical radiation schedule. This differential effect has also been observed following ingestion of a toxin and the injection of a drug (Garcia & Koelling. 1965).Apparently this differential effectiveness of cues is due either to the nature of the reinforcer. i.e .• radiation or toxic effects. or to the peculiar relation which a gustatory stimulus has to the drinking response. ·i.e .• gustatory stimulation occurs if and only if the animal licks the fluid. The environmental cues associated with a distinctive place are not as dependent upon a single response of the organism. Therefore. we made an auditory and visual stimulus dependent upon the animal's licking the water spout. Thus. in four experiments reported here "bright-noisy" water. as well as "tasty" water was conditionally paired with radiation. a toxin. immediate shock, and delayed shock. respectively. as reinforcers. Later the capacity of these responsecontrolled stimUli to inhibit drinking in the absence of reinforcement was tested.Psychon. Sci., 1966, Vol. <1 MethodThe apparatus was a light and sound shielded box (7 in. x 7 in. x in.) with a drinking spout connected to an electronic drinkometer which counted each touch of the rat's tongue to the spout. "Brightnoisy" water was provided by connecting an incandescent lamp (5 watts) and a clicking relay into this circuit. "Tasty" water was provided by adding flavors to the drinking s...

In regulating the internal homeostatic environment mammals, by necessity, employ behavioral strategies that differ from the tactics used in coping with contingencies in the external environment. When an animal consumes a meal, the palatability of that meal is automatically adjusted in accordance with the ultimate internal effects of that meal. If the meal causes toxicosis, the animal acquires an aversion for the taste of the meal; conversely, if recuperation follows ingestion of the meal, the taste of that meal is enhanced. Unlike the learning that occurs when externally referred visual and auditory signals are followed by punishment in the form of peripheral pain or reward in the form of food in the mouth, conditioning to the homeostatic effects of food can occur in a single trial and rarely requires more than three to five trials, even though the ultimate effects of the meal are delayed for hours. Paradoxically, the animal need not be aware of the ultimate internal effect in the same sense that it is aware of external contingencies. For example, an aversion can be acquired even if the animal is unconscious when the agent of illness is administered. Thus, the way in which food-effects are stored in memory may be fundamentally different from the way in which memories of specific time-space strategies devised for external contingencies are stored. This separation of function is indicated by limbic lesions which disrupt conditioning to a buzzer that is followed by shock and facilitate conditioning to a taste that is followed by illness. Operationally speaking, one can describe both aversion conditioning and buzzer-shock conditioning in the spacetime associationistic terms of classical conditioning. However, psychologically speaking, one must realize that in aversion conditioning the animal does not act as if it were acquiring an "if-then" strategy. It acts as if a hedonic shift, or a change in the incentive value of the flavor were taking place. Such hedonic shifts are critical in regulation of the internal milieu. When an animal is in need of calories, food tends to be more palatable; as the caloric deficit is restored, food becomes less palatable. If the animal's body temperature is below optimum, a warm stimulus applied to the skin is pleasant. When body temperature is too high, the converse is true. In this way, homeostatic states monitored by internal receptors produce changes in the incentive values of external stimuli sensed by the peripheral receptors, and guide feeding behavior. In mammals at least, the gustatory system, which provides sensory control of feeding, sends fibers to the nucleus solitarius. This brainstem relay station also receives fibers from the viscera and the internal monitors of the area postrema. Ascending fibers bifurcate at the level of the pons and project toward the feeding areas of the hypothalamus and the cortex. The olfactory system which primarily projects to the limbic system does not play a primary role in adjusting food incentives. Rather, it plays a secondary role in the acti...

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HARVARD MEDICAL SCHOOL AND NEUROSURGICAL SERVICE, MASSACHUSETTS GENERAL HOSPITALGustatory aversions, induced in rats by conditionally pairinfl a distinctive flavor with a noxious drug, were readily established wen when injections were delayed an hour or more. The optimal interstimulus interval and effectiveness of cues for learning appear to be a function of the specific effects of the reinforcer on the organism.It is considered axiomatic in theory and practice that no learning will occur without immediate reinforcement. For example, a hungry rat will not learn to press a lever for food unless the response is immediately followed by food (primary reinforcement) or by a signal which has been associated with food in the past (secondary reinforcement). Food can be described as rewarding, but the same general rule has been applied to punishing agents also. Delays of the order of 3 to 45 sec. have a deleterious effect upon learning in a wide variety of experimental situations. The significance of these findings for reinforcement theory was discussed by Spence (1947) and a recent review (Renner, 1964) reveals there has been no major modification of the temporal contiguity aspect. However, our data indicates that immediate reinforcement is not a general requirement for all learning. MethodYoung adult male rats (Sprague-Dawley, 300 to 400 gm)were maintained in individual cages with Purina Laboratory Chow ad lib. Drinking was restricted to a 10-min, period each day. After one week of habituation to this schedule, treatment began. In Experiment A, five groups (N = 8 each) were treated. One experimental group (Sac-Apo:inj) was given a gustatory cue in its drinking water (1 gm saccharine per liter) and after a delay was injected with a drug which produced gastriC disturbances (7mg/kg apomorphine hydrochloride I.P.). The animals were injected in serial order at I-min. intervals with the first animal injected at 5 min. and the last one at 12 min. after the saccharin water bottle was removed from the home cage. One control group (Sac-Sal:inj) drank saccharinwater and was injected with saline, while another control (Wat-Apo:inj) drank water and was injected with apomorphine. An additional experimental group (SacApo:inj) received delayed injections in serial order from 15 to 22 min. post-drinking. Other rats (Sac-Shock), immediately after drinking saccharin -water, were taken from their cages and placed in a box with an electric grid floor and three shocks (0.5 sec. pulses at 3 mal were delivered within 1 min. to the paws.All groups received four treatments, one every third day and then three extinction tests (Le. no injections or shock) on the same schedule. Between treatment days, the animals were given water for 10 min.