Neophobias and conditioned taste aversions in rats following exposure to novel flavors

Abstract

Rats were successively exposed to three solutions with distinctively different flavors and then tested for both neophobia and propensity to form conditioned taste aversions to a fourth distinctively flavored solution. All permutations between the four solutions (salty, bitter, sweet, and sour) were examined. The prior exposures resulted in attenuation of neophobia to novel salty and sour solutions, but not to equally novel bitter or sweet solutions.. These effects were found to depend upon the diversity of the prior ingestive events rather than upon either a single specific flavor experience or a summation of the reductions in generalized neophobia accrued by each substance separately; both of the latter findings are inconsistent with stimulus generalization being responsible for the observed attenuation of neophobia to salty and sour solutions following exposure to diverse different solutions. A further test of generalization between the salty and bitter solutions, consisting of associating one flavor with poison and extinguishing the avoidance response in half the animals prior to testing for generalization of conditioned taste aversion to the other flavor, also proved negative. Although these effects of exposure to flavors distinctly different from the test solution may be dependent upon solution concentrations, further research found that the same pretest exposures and same test concentrations failed to inhibit formation of conditioned taste aversions. A demonstration of "latent inhibition" attested to the sensitivity of our procedure to potential interference with acquisition of conditioned taste aversions. The results are considered in light of the relationship between neophobia and conditioned tasted aversions, the differential biological relevancy of specific tastes, and abstraction as a cognitive capability of rats. The possibility is raised that the defense against toxins is not the primary function of neophobia. Barnett and Cowan (1976) argue that neophobia is prominent among rats owing to their varied diets and perhaps augmented by the selective pressure of man's attempt to control them with poison. They contend that neophobia may have evolved in rats specifically because of the high likelihood of toxins' occurring in novel, untried substances. This view cannot readily explain the finding that exposure to novelty per se, that is, a varied diet, decreases neophobia to all novel substances, including items that are quite dissimilar to any component of the varied diet (e.g., Braveman & Jarvis, 1978). Moreover, Barnett and Cowan (1976), among others, have suggested, on the theoretical grounds of common function, that neophobia and conditioned taste aversion (CTA) are merely different points on a common dimension of aversive-

Effects of pretraining on conditioning-enhanced neophobia: Evidence for separable mechanisms of neophobia and aversion conditioning

“…These results support the view that novelty may reflect a general process that is not necessarily related to the flavor-specific properties (e.g., taste or intensity) of the stimuli used (Miller & Holzman, 1981). The nonspecific character of novelty conceivably may have permitted the influence of novel flavor preexposure to endure the acquisition ofCTA.…”

“…In Experiments lb and 2b, prior "safe" ingestion of novel saline or saccharin reduced the demonstration of conditioning-enhanced neophobia to casein hydrolysate. Because this effect occurred without apparent diminution of CTA to the novel CS, it appears that prior ingestion history affects neophobia through a process which differs from that by which prior ingestion experience affects CTA (see Braveman &Jarvis, 1978, andMiller &Holzman 1981). …”

Age dependency in neophobia: Its influence on taste-aversion learning and the flavor-preexposure effect in rats

“…Our results also appear at odds with a growing body of data being interpreted as indicating the "independence" (Braveman & Jarvis, 1978) or "decoupling" (Miller & Holzman, 1981) of flavor neophobia and conditioned taste aversion. These investigators have shown that familiarization procedures that reduce neophobia can leave CT A unaltered.…”

“…Thus, had US intensity been less or preexposure duration greater in the Braveman-Jarvis and Miller-Holzman studies, the attenuating effect of preexposure on conditioning and, hence, the contribution of neophobia to CTA would have been evident. In fact, Tarpy and McIntosh (1977) had previously shown that the familiarization procedure used by Braveman and Jarvis (1978) and Miller and Holzman (1981) to reduce neophobia also alters CTA if familiarization is extensive. Thus, it would appear that unlearned fear of novel flavors is, in most cases, simply weaker than conditioned fear and, hence, is altered more easily than CTA by factors that influence fear.…”

Roles of visual and taste cues in ingestional neophobia: Response latency effects in chicks (Gallus domesticus)

“…Ingestional neophobia refers to the finding that initial presentation of novel food/drink yields minimal intake relative to that after repeated access (see, e.g., Braveman, 1978;Miller & Holzman, 1981). The unfamiliar appearance of an ingestible may produce neophobia because unfamiliar visual cues may deter approach and, thus, deter the start of ingestion.…”