Three experiments investigated the effect of age and degree of learning on short-term retention (up to 24 hr.) of one-way active-avoidance learning. Following training to a single avoidance, rats aged 25 days or older uniformly showed poorer retention after intermediate retention intervals (1 or 4 hr.) than immediately after training (5-10 min.) or later (24 hr.), i.e., a "Kamin effect." This effect was not observed with younger Ss previously trained to a single avoidance. With increased level of original training, the Kamin effect was present in rats aged 15-18 days. Fear-based hormonal explanations of this effect may be inadequate in view of the apparently underdeveloped hormonal system at this age.Recently there has been a revival of interest in retention as a function of age. Kirby (1963) demonstrated that the retention of an active-avoidance response for 25-day-old Ss was equal to that of 50and 100-day-old Ss on a 24-hr, test but was inferior to that of older Ss on 25and 50-day tests. These age-related retentional differences found only after intervals longer than 24 hr. have been reproduced in escape learning (Smith, 1963), fear conditioning (Campbell & Campbell, 1962), and discrimination learning (Campbell, 1967; Campbell, Jaynes, & Misanin, 1968;Smith, 1968). However, there may be some situations in which there are age differences at retention intervals of 24 hr. or less; for example, rats younger than those tested in the previous studies might show retention differences on a 24-hr, test.An age-dependent "Kamin effect" must also be considered as a possible source of performance differences on short-term retention tests. The Kamin effect consists of an initial decrement in avoidance per-

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Four studies were conducted to explore the effects of unpaired lithium chloride (LiCl) injections, the unconditioned stimulus (US), on the acquisition and retention of a taste aversion. In Experiment 1, subjects were preexposed to a US; for one group the US was paired with a distinctive taste, whereas for a second group it was not. Following this preparation, both groups received the US paired with a novel taste. Only the US-alone group showed a retardation of subsequent taste-aversion conditioning. Experiment 2 indicated that an exposure to LiCl without a specific gustatory cue will interfere with the avoidance of a specific taste, regardless of whether the US experience occurs before or after a single taste-LiCl pairing. Following sucrose-LiCl pairings in Experiment 3A, LiCl-alone exposures retroactively interfered with the retention of the prior aversion to sucrose, with the level of post-US interference becoming an increasing function of the number of US-alone experiences. In Experiment 3B, the association of sucrose with LiCl did not interfere with the development of an almond aversion, whereas LiCl-alone exposures following the acquisition of a sucrose aversion proactively interfered with the development of a second taste aversion (almond). It is suggested that a physiological explanation will not adequately account for the present results of these experiments. The results are discussed within the framework of alternative associative models.

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