Alfredo Espinet

Perceptual learning enhances retrospective revaluation of conditioned flavor preferences in rats

Forward and backward blocking of taste preference learning was compared in rats. In the forward condition, thirsty rats were exposed to a flavor (A) in sucrose solution (+) or in water (-), after which they were exposed to A in compound with another flavor (B) in sucrose solution (i.e., AB+). In the backward condition, these phases were reversed. Consumption of B alone was assessed when rats were food deprived. In the forward condition, rats given A+ consumed less B than rats given A-, providing evidence of forward blocking, whereas in the backward condition, rats given A+ drank more of B than those given A-. Subsequent experiments found that alternating but not blocked preexposure to A and B, when given prior to training, produced blocking of B whether A+ was given before or after AB+, suggesting that prior failures to observe backward blocking reflect failures of discrimination.

Effects of neonatal handling on playfulness by means of reversal of the desire to play in rats (Rattus norvegicus).

In the present study the authors sought to establish whether the range of effects of neonatal handling stimulation (H), that is, brief daily periods of infant isolation, could be extended to the domain of social motivation. With this aim, the authors studied the innate motivation to engage in rough-and-tumble play (R&T) in adolescent rats (Rattus norvegicus) by means of a reversal design, in which half of the rats were first housed in isolation (Days 1-3), and then in company (Days 4-6), while the other half followed the reverse sequence of housing conditions. Results showed in a clear-cut manner that H fuelled playfulness, as measured by pin and dorsal contact episodes, with (relative) independence of trait-based differences in fearful behavior between handled and nonhandled rats. Given that the different levels of the rats social brain are apparently sensitive to tactile stimulation in infancy, the authors propose that the vibrant R&T reported here could reflect an enduring alteration of genetically based, motivational systems underlying playfulness and, perhaps, positive social emotions like joy.

Inhibitory sensory preconditioning

In two experiments rats were preexposed to neutral stimuli. Both experiments used a between-subjects design in which a paired group was preexposed to intermixed presentations of A→ Band AX, and an unpaired control group was preexposed to intermixed presentations of A, B, and AX. After the conditioning of B, in Experiment 1, conditioned responding to X was acquired more slowly in the paired than in the unpaired group. Furthermore, in Experiment 2, Xreduced conditioned responding to a separately trained excitor in a summation test but only in the paired group. Together, these results provide evidence of an inhibitory form of sensory preconditioning.

Generalization Decrement and Not Overshadowing by Associative Competition Among Pairs of Landmarks in a Navigation Task

When they are trained in a Morris water maze to find a hidden platform, whose location is defined by a number of equally spaced visual landmarks round the circumference of the pool, rats are equally able to find the platform when tested with any two of the landmarks (Prados, & Trobalon, 1998; Rodrigo, Chamizo, McLaren, & Mackintosh, 1997). This suggests that none of the landmarks was completely overshadowed by any of the others. In Experiment 1 one pair of groups was trained with four equally salient visual landmarks spaced at equal intervals around the edge of the pool, while a second pair was trained with two landmarks only, either relatively close to or far from the hidden platform. After extensive training, both male and female rats showed a reciprocal overshadowing effect: on a test with two landmarks only (either close to or far from the platform), rats trained with four landmarks spent less time in the platform quadrant than those trained with only two. Experiment 2 showed that animals trained with two landmarks and then tested with four also performed worse on test than those trained and tested with two landmarks only. This suggests that generalization decrement, rather than associative competition, provides a sufficient explanation for the overshadowing observed in Experiment 1. Experiment 3 provided a within-experiment replication of the results of Experiments 1 and 2. Finally, Experiment 4 showed that rats trained with a configuration of two landmarks learn their identity.

Order effects after blocked preexposure to two compound flavors.

In the first three experiments two groups of rats received prolonged blocked preexposure to AX-BX or to BX-AX. Experiment 1 showed that conditioning of AX after preexposure resulted in less generalization to BX in the AX-BX group than in the BX-AX group. Experiments 2 and 3 constituted, respectively, retardation and summation tests of the inhibitory properties acquired by B after preexposure and conditioning of A. Excitatory conditioning of B was retarded in the AX-BX group (Experiment 2) and only in this group B was able to alleviate the aversion conditioned to a new stimulus (Experiment 3). These results are explained as a consequence of the formation, in the AX-BX group, of inhibitory associations directed from B to A. A fourth experiment provided evidence that the A↔X association was preserved until the end of the preexposure phase in this group, which is a requisite for the formation of these inhibitory associations.

Inhibitory sensory preconditioning detected with a sodium depletion procedure

In each of two experiments, two groups of rats were exposed to three flavoured solutions: A (citric acid), B (salt), and AX (a compound of citric acid and saccharin). Both experiments used a between-subjects design in which a paired group received presentations of A followed by B, alternating with presentations of AX (i.e., A → B/AX), and an unpaired group received alternating presentations of A, B, and AX (i.e., A/B/AX). This arrangement was expected to establish X as an inhibitor of B in group paired but not in group unpaired. In Experiment 1, after preexposure all subjects received a single presentation of an XB compound, then experienced sodium depletion, and were tested for their consumption of X, which was greater in group unpaired than in group paired. In Experiment 2, after preexposure, all subjects received four presentations of a new flavour, C, in compound with B and subsequently, under sodium depletion, were tested for consumption of XC. Intake of the XC compound was less in group paired than in group unpaired. These results suggest that, in group paired, X acquired an inhibitory relationship with B both retarding the acquisition of an excitatory association with B (retardation test, Experiment 1) and reducing the response to a new stimulus, C, strongly associated to B (summation test, Experiment 2). These results provide direct evidence of inhibition between two neutral stimuli and, therefore, of inhibitory sensory preconditioning.

Preservation of within-compound associations after blocked preexposure to two compound flavors.

Three experiments investigated the extinction of the within-compound A↔X association established when two compound flavors, AX and BX, are preexposed in blocks (i.e., AX, AX, AX, ... BX, BX, BX). In Experiment 1, a group of rats received preexposure to a block of AX trials followed by a second block of BX trials (AX-BX), while a second group received blocked preexposure to the same stimuli in the opposite order (BX-AX). Subsequently, flavor A was paired with lithium chloride. This conditioning resulted in a similar reduction of consumption of flavor X in both groups. In Experiment 2 four groups of rats received blocked preexposure to AX-BX, AX-B, A-BX, or A-X. After aversive conditioning of X, consumption of A and B was significantly lower for the groups which received these flavors paired with X than for the groups for which these flavors were presented isolated. In Experiment 3 a group of rats was preexposed to a block of SaltX presentations followed by a block of BX presentations (SaltX-BX), and a second group received blocked preexposure to (BX-SaltX). After subsequent sodium depletion, consumption of X was high and similar for the SaltX-BX and for the BX-SaltX groups. These results indicate that the within-compound association established in the first block of a blocked preexposure is not extinguished when the preexposure phase is concluded.

PERCEPTUAL LEARNING BY PRESCHOOL CHILDREN USING STIMULI WITH VARYING PROPORTIONS OF COMMON ELEMENTS

The effect of preexposure to visual stimuli on subsequent discrimination was studied in 17 girls and 23 boys, ages 53 to 61 mo., using a test in which a sample stimulus had to be identified from a set of comparison stimuli. Preexposure significantly facilitated discrimination. This facilitation was more noticeable between stimuli which shared a large proportion of common elements. The results were consistent with an associative theory of the representation of stimuli suggested by McLaren, Kaye, and Mackintosh in 1989, and implications are considered for teaching.

Extinction of the initial within-compound association established in a blocked preexposure to two compound flavours

Abstract Extinction of the A↔X association after blocked preexposure to AX-BX was studied in two experiments. In Experiment 1, two groups of rats received long (14 trials) or short (4 trials) blocked preexposure to AX-BX and subsequent conditioning of X. The results showed that the AX association was equally preserved after long and short preexposure. Experiment 2 studied the effect of blocked preexposure to 0, 1 or 2 ruptures of the AX association on extinction. In this experiment a “rupture” is produced when, in subsequent blocks, one element of the original compound is presented in compound with a different element. A significant extinction was observed only when the AX association was broken twice

Taste discrimination after separate pre-exposure and test sessions.

The effect of previous exposure on discrimination of two flavored solutions sharing a common taste was investigated in a pilot experiment. These solutions were at the limit of discrimination and the pre-exposure and test phases took place on different days. The results showed that mere pre-exposure (i.e., in absence of feedback) facilitates subsequent discrimination of same or different pairs of solutions. This result is in some aspects opposite to those reported recently by Dwyer and colleagues. This discrepancy is discussed analyzing the procedural differences observed between these studies.