Two experimental paradigms are presented aimed at determining the retention of auditory and visual information over brief delay intervals. First, a conditional delayed matching-tosample procedure was used in which rats were required to symbolically match the modality of the sample stimulus with one of two comparison stimuli. In the second experiment, subjects were trained and tested using a Konorski-type procedure. Despite the conceptual and procedural differences between the two procedures, subjects in both experiments showed steeper forgetting functions for visual events than for auditory events, while performance levels at O-sec delay intervals were equivalent for both stimuli. These results, when taken together with related research conducted with pigeons, suggest that content of memory may have important influenceson the short-term retention abilities of animal subjects.Surprisingly little is known about forgetting of recent events in the laboratory rat. Although Hunter (1913) reported that rats could retain the spatial location of visual stimulus representing food for a maximumof 10 sec, successful performance appeared to be dependent upon the use of response-directing behaviors which mediated the delay. More recent investigators have modified Hunter's procedure and have studied short-term retention using delayed response and delayed alternation tasks (e.g., Gordon, Brennan, & Schlesinger, 1976;Roberts, 1974). These paradigms have been problematic, however, primarily because they do not allow for precise experimental specification of the event the rat is required to retain. While the delayed matching-to-sample (DMTS) task has proven to be a useful method for measuring

The retention and extinction of a conditioned taste aversion after either short (6-day) or long (60-day) intervals was investigated in preweanling (I8-day-old) and adult rats. Taste-only and illness-only control conditions were employed, as were variations in the concentration of the US (holding Liel amount constant). Results indicated that after the short retention interval, retention of the taste aversion was equivalent for both ages. After the long interval, however, the I8-day-old rats exhibited significantly weaker taste aversion than their adult counterpartsinfantile amnesia. Manipulation of US concentration had no effect on the magnitude of the taste aversions for either age or retention interval. The results are discussed in terms of their implications for infantile amnesia and general laws of learning.Immature animals forget at a faster rate than do more mature animals (for reviews, see Campbell & Campbell & Spear, 1972;Spear, 1978Spear, , 1979, and this probably is also true for humans (Cohen & Gelber, 1975;Levy, 1960;Pancratz & Cohen, 1970). This accelerated rate of forgetting by younger organisms has been termed infantile amnesia. However, some recent evidence suggests that less infantile amnesia may occur when the information to be retained involves a particular class of events that may constitute a "highly prepared" association (Coulter, Collier, & Campbell, 1976;Spear, 1978). Ontogenetic studies of conditioned taste aversion (Campbell & Alberts, 1979; Klein, Mikulka, Domato, & Hallstead, 1976) provide some of the more convincing of this evidence.While long-term retention of taste-illness associations by adults is excellent (Biederman, Milgram, Heighington, Stockman, & O'Neil, 1974;Dragoin, Hughes, Devine, & Bentley, 1973), the data with respect to immature organisms are mixed. Specifically, Klein et al. (1976), using postweanling rats (23-dayold), and Campbell and Alberts (1979), who used preweanling (18-day-old) infant rats, have demonstrated retention equivalent to that of adults over retention intervals of 28 and 56 days. However, with rat pups 10 and 12 days of age, Campbell and Alberts (1979) did find poorer retention across long intervals. Both of these studies used LiCI as the unconditioned stimulus (US) and employed a singlebottle testing procedure. The data obtained with Preparation of this article was supported by grants from the National Science Foundation (BNS 74-24194 and BNS 78-02360) to the third author. We thank Norman "Richter for technical advice and assistance and Teri Tanenhaus for preparation of the manuscript. Requests for reprints should be sent to Norman E. Spear, Department of Psychology, State University of New York at Binghamton, Binghamton, New York 13901. these procedures suggest that, by 18 days of age, rat pups have attained adult levels of retention for a taste-illness association. In contrast to the findings of Campbell and Alberts (1979), Ader and Peck (1977) and Peck (Note 1) have reported relatively poor retention of all early (Zl-day-old rat pup) taste-ill...

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Eight experiments using 611 rats as subjects were conducted to define and analyze an age-related phenomenon of conditioned taste aversion. When consumption of sucrose solution was followed by LiCl-induced illness in the animals' home, acquisition of the aversion to sucrose solution was retarded in preweanling (18-day-old) rats. This effect was not found in adults or in slightly older (21-day-old) rats. Place of testing had no effect in the younger two age-groups, but in adults manifestation of the acquired aversion was retarded when they were tested in the home. There was no interaction between place of conditioning and testing for any age. The locus of the environmental influence on conditioning in preweanling rats was found to be the place of tasting rather than place of illness, retention interval, or testing. Also, the effect was found to be invariant under minor variations in familiarization of the animal with the non-home environment. The principle emerging from these data and others is that the home environment can have a significant influence on learning and conditioning in the immature rat.Recent developmental psychobiological research with altricial mammals has taken a systemogenesis approach (Anohkin, 1964) and focused on functional systems as they emerge. More specifically, those investigations concerned with the ontogeny of learning and retention have studied sensory and motor systems that are functional early in life. Kenny and Blass (1977), for example, demonstrated learning and 24-hr retention of a position discrimination by 7day-old rat pups when reinforcement consists of contact with the mother and suckling on a dry nipple, and Rudy and Cheatle (1977) found learning and 6-day retention of an odor aversion by 2-day-old rat pups. More recently, Johanson and Hall (1979) reported the acquisition of an operant dis-Preparation of this article was supported by grants from the National Science Foundation (BNS 74-24194 and BNS 78-02360) to the third author. We would especially like to thank Norman Richter for technical advice and assistance, and Teri Tanenhaus for preparation of the manuscript.

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