Temporal properties of responding during stimuli that precede response-independent food

Pigeons' keypecks were reinforced with grain on the average of once per minute by schedules that maintained low response rates and by schedules that maintained high response rates. During these schedules, a fixed-duration conditioned stimulus (CS) ranging from 7.5 to 120 sec in duration across conditions terminated with response-independent food. Response rates during the CS were inversely related to CS duration. The rates and the temporal patterns of responding during the shortest CS were similar whether the ongoing schedule maintained high response rates or low response rates. As CS duration increased, the rate and pattern of responding during the CS converged on the rate and pattern of responding maintained by the baseline schedule. These data indicate that changes in responding during stimuli that signal response-independent reinforcement are not homogeneous throughout the CS; that response measures, such as “suppression ratios”, which presume homogeneity may mislead us; and that conditioned suppression and conditioned enhancement may be better talked about in terms of species-specific approach and avoidance than in terms of emotional states.     

Development switch in neural circuitry underlying odor-malaise learning

Fetal and infant rats can learn to avoid odors paired with illness before development of brain areas supporting this learning in adults, suggesting an alternate learning circuit. Here we begin to document the transition from the infant to adult neural circuit underlying odor-malaise avoidance learning using LiCl (0.3 M; 1% of body weight, ip) and a 30-min peppermint-odor exposure. Conditioning groups included: Paired odor-LiCl, Paired odor-LiCl-Nursing, LiCl, and odor-saline. Results showed that Paired LiCl-odor conditioning induced a learned odor aversion in postnatal day (PN) 7, 12, and 23 pups. Odor-LiCl Paired Nursing induced a learned odor preference in PN7 and PN12 pups but blocked learning in PN23 pups. 14C 2-deoxyglucose (2-DG) autoradiography indicated enhanced olfactory bulb activity in PN7 and PN12 pups with odor preference and avoidance learning. The odor aversion in weanling aged (PN23) pups resulted in enhanced amygdala activity in Paired odor-LiCl pups, but not if they were nursing. Thus, the neural circuit supporting malaise-induced aversions changes over development, indicating that similar infant and adult-learned behaviors may have distinct neural circuits.     

Learned irrelevance and retrospective correlation learning

In 1973 Mackintosh reported an interference effect that he called learned irrelevance in which exposure to uncorrelated (CS/US) presentation of the unconditional stimulus (US) and the conditioned stimulus (CS) interfered with future Pavlovian conditioning. It has been argued that there is no specific interference effect in learned irrelevance; rather the interference is the sum of independent CS and US exposure effects (CS + US). We review previous research on this question and report two new experiments. We conclude that learned irrelevance is a consequence of a contingency learning and a specific learned irrelevance mechanism. Moreover even the “independent exposure controls”, used in previous experiments to support the CS and US exposure account, provide support for the correlation learning process.     

Animal learning of independent and correlated events

Evidence suggests that experience of a truly random presentation of a conditioned and unconditioned stimulus (CS and US) retards subsequent acquisition of a classically conditioned response when the CS and US are paired. In these studies, no events reliably predict the US during the first part of training. The present experiment demonstrated impairment of subsequent appetitive conditioning in rats following a random CS-US presentation, both when another predictive cue is present and when it is absent during this experience. Results are discussed with reference to “general attention” theory, and learned helplessness. However, the data support an interpretation in terms of learning a specific relationship between a particular CS and US.     

Potentiation and overshadowing in preweanling and adult rats

Four experiments compared the aversion acquired by 18-day-old and 60-day-old rats to a flavor that was either tasted alone or in combination, simultaneously or successively, with another flavor when paired with illness. The purpose was to study temporal variables and theoretical issues pertinent to potentiation and overshadowing while investigating ontogenetic differences in these phenomena. When either the preweanlings or the adults were presented a simultaneous compound flavor (sucrose/coffee) followed by lithium chloride-induced illness, greater sucrose aversions were found than for animals conditioned on sucrose alone--that is, potentiation. Preweanlings demonstrated greater potentiation than did adults, whether the conditioned stimulus-unconditioned stimulus (CS-US) delay was 0 or 1 hr. This potentiation was eliminated by nonreinforced presentations of the alternative CS element. Potentiation was not seen when the two flavors were presented successively as the CS; instead, overshadowing occurred. Tests of configuring by extinction procedures indicated a tendency for these animals to form a configured representation of the simultaneous compound solution. This disposition for configuring tended to be more pronounced for preweanlings than for adults. Ontogenetic differences in response to configuration, CS saliency, and generalization decrement seem consistent with at least one model of potentiation and the ontogenetic differences in potentiation seen in the present experiments.     

The importance of contextual elements in taste-aversion learning

The effect of exteroceptive contextual cues, presented during the conditioned stimulus (CS) and unconditioned stimulus (US) intervals, upon the later development of conditioned saccharin aversions was studied in two experiments. It was found that the presence of the contextual cues during the CS + US and CS intervals resulted in a greater degree of saccharin aversion; the presence of these cues during the US interval was relatively less important. These findings are discussed in terms of conditioning models and retrieval models derived from animal learning and human information-processing data.     

Across-reinforcement blocking effects in a mediational test of the CS's general signaling property

Rats received Pavlovian aversive (shock) conditioning in which white noise was established for independent groups as a CS+, CSo, or CS−. Then, in an easy (light-dark) T-maze discrimination, the CS was presented either immediately following choice (Locus 1) or at the food cup in the goal (Locus 3), contingent upon either a food-reinforced (right) or nonreinforced (wrong) response. When presented at Locus 3, the CS+ facilitated and the CS− retarded learning for CS/right subjects, with these effects being exactly reversed but somewhat less pronounced for CS/wrong subjects. However, when the CS was presented at Locus 1, the CS+ and CS− effects for both response contingencies were attenuated. These findings oppose an interpretation of the CS's function as a general cue or transformed signal for the presence or absence of the new appetitive reinforcer and argue instead for across-reinforcement blocking effects: By signaling in the presence of food reinforcement an outcome (safety or shock) which is consonant with or discrepant from the “good” outcome obtained, the CS− blocks (retards) and the CS+ counterblocks (enhances) the association of food reinforcement and the S^D; conversely, in the presence of nonreinforcement (a “bad” outcome), the CS− counterblocks and the CS+ blocks inhibitory conditioning to the S^Δ. As in Kamin's (1968) original research, such effects are attenuated when the CS is presented early in the compound, distal to the reinforcer.     

The influence of flavor preexposure and test interval on conditioned taste aversions in the rat

The effects of flavor preexposure and test interval on conditioned taste aversions were examined in four experiments. In the first three experiments, prior experience with a flavor different from that used as a conditioned-stimulus (CS) produced attenuated aversions when testing occurred after a 1-day interval but not after a 21-day interval. Preexposure to the same stimulus used as a CS produced attenuated aversions at both 1- and 21-day intervals. In Experiment 4, a delay interval between flavor preexposure and conditioning eliminated the attenuating effect of preexposure, but only when different stimuli were used for preexposure and conditioning. These data could not be easily accounted for by contemporary interpretations of preexposure as an event that interferes with subsequent acquisition of a conditioned aversion. An alternative retrieval interference hypothesis was outlined.     

Odor-aversion learning in neonate rat pups: the role of duration of exposure to an odor

Five experiments employed 2- and 10-day-old rat pups to examine the ontogeny of odor-aversion learning. When duration of exposure to the to-be-conditioned odor stimulus (CS) was long, Experiments 1 and 2 demonstrated substantial and similar aversions across the two ages regardless of whether the toxin unconditioned stimulus (US) occurred simultaneously with, immediately before, immediately after, or some time after the CS. These experiments, therefore, did not support the claim of Rudy and Cheatle (Ontogeny of Learning and Memory. Hillsdale, N.J.: Erlbaum (1979) ) that the 2-day old pup suffers a deficit in its learning about the relation between successively presented events. The remaining experiments showed, however, that the 2-day-old pups did not acquire an aversion to a briefly presented CS, that the failure to condition this CS was not due to its overshadowing by contextual cues, and that the 10-day-old pup did acquire an aversion to that CS. The experiments have revealed, therefore, that there are age-related differences in the rat pup's ability to learn about the relation between a briefly-presented CS and the effects of a US.     

Ontogenetic differences in the association of gustatory and tactile cues with lithium chloride and footshock

Using a double dissociation design with 15% sucrose solution and exposure to a heat lamp (34 degrees C) as CSs and 0.3 M LiCl and 1-mA footshock as USs, the present study found 15-day-old rats to show selective associations similar to those found in adults. Five-day-old pups, however, expressed similar sucrose aversions when this solution was paired with either LiCl or footshock, whereas they expressed heat aversions after heat-LiCl but not heat-shock pairings. Results are discussed with respect to previous data on selective associations in pups, current theories on selective associations, and ontogenetic differences in stimulus selection.     

Ontogenetic change in the auditory conditioned stimulus pathway for eyeblink conditioning

Two experiments examined the neural mechanisms underlying the ontogenetic emergence of auditory eyeblink conditioning. Previous studies found that the medial auditory thalamus is necessary for eyeblink conditioning with an auditory conditioned stimulus (CS) in adult rats. In experiment 1, stimulation of the medial auditory thalamus was used as a CS in rat pups trained on postnatal days (P) 17-18, 24-25, or 31-32. All three age groups showed significant acquisition relative to unpaired controls. However, there was an age-related increase in the rate of conditioning. Experiment 2 examined the effect of inactivating the medial auditory thalamus with muscimol on auditory eyeblink conditioning in rats trained on P17-18, 24-25, or 31-32. Rat pups trained on P24-25 and P31-32, but not P17-18, showed a significant reduction in conditioned responses following muscimol infusions. The findings suggest that the thalamic contribution to auditory eyeblink conditioning continues to develop through the first postnatal month.     

Learned irrelevance: A contemporary overview

This article reviews the recent literature on the topic of learned irrelevance. It asks whether the retardation of subsequent conditioning produced by uncorrelated preexposure is indeed the result of the animal learning that a conditioned stimulus (CS) and unconditioned stimulus (US) are unrelated, or whether it is better explained either as a result of the context specificity of latent inhibition, or as some other artefact of the uncorrelated schedule employed. The conclusion is that there is as yet no good evidence to support the existence of a “genuine” learned irrelevance effect.     

Acquisition of representation-mediated conditioned food aversions

Food aversions were established in rats by administering lithium chloride (LiCl) immediately after the presentation of an exteroceptive conditioned stimulus (CS) which previously had been paired with a food substance. In Experiment 1, rats which received first tone-food and then tone-LiCl pairings showed less food consumption in subsequent testing than rats which received only tone-food or tone-LiCl pairings. Experiments 2 and 3 demonstrated the stimulus specificity of aversions established in this manner. Rats which first received pairings of light and tone CSs with two different food substances and then received pairings of one of those CSs with LiCl showed greater aversion to the food previously associated with the LiCl-paired CS than to the other food substance. Experiment 3 also showed that specific aversions were not acquired if rats received CS-shock rather than CS-LiCl pairings. These results suggest that CS-evoked representations of events can substitute for those events themselves in the formation of new associations.     

Nicotinic modulation of tone-evoked responses in auditory cortex reflects the strength of prior auditory learning

Nicotinic acetylcholine receptors (nAChRs) contribute to sensory-cognitive function, as demonstrated by evidence that nAChR activation enhances, and nAChR blockade impairs, neural processing of sensory stimuli and sensory-cognitive behavior. To better understand the relationship between nAChR function and behavior, here we compare the strength of nAChR-mediated physiology in individual animals to their prior auditory behavioral performance. Adult rats were trained on an auditory-cued, active avoidance task over 4 days and classified as “good,” “intermediate” or “poor” performers based on their initial rate of learning and eventual level of performance. Animals were then anesthetized, and tone-evoked local field potentials (LFPs) recorded in layer 4 of auditory cortex (ACx) before and after a test dose of nicotine (0.7 mg/kg, s.c.) or saline. In “good” performers, nicotine enhanced LFP amplitude and decreased response threshold to characteristic frequency (CF) stimuli, yet had opposite effects (decreased amplitude, increased threshold) on responses to spectrally distant stimuli; i.e., cortical receptive fields became more selective for CF stimuli. In contrast, nicotine had little effect on LFP amplitude in “intermediate” or “poor” performing animals. Nicotine did, however, reduce LFP onset latency in all three groups, indicating that all received an effective dose of the drug. Our findings suggest that nicotinic regulation of cortical receptive fields may be a distinguishing feature of the best-performing animals, and may facilitate sensory-related learning by enhancing receptive field selectivity.     

Aversive CSs suppress lever pressing for food but not the eating of free food

Forty rats received CER acquisition, half “on the baseline” (response lever present), half “off the baseline.” During initial CER extinction, Ss received: (a) normal CER extinction (lever available), (b) free food during CSs only (no lever), (c) free food during non-CSs only (no lever), or (d) free food during both CS and non-CS periods (no lever). While normal extinction Ss were highly suppressed in the presence of the CS, all free food groups readily ate but did not differ in eating latencies. On subsequent CER extinction trials on the baseline, those Ss which received free food during the CSs were no less suppressed than other Ss. These data offer no support for Estes' (1969) reciprocal inhibition explanation of CER and punishment, nor do they support a fear interpretation of CER.     

Effects of Early Hippocampal Lesions on Trace, Delay, and Long-Delay Eyeblink Conditioning in Developing Rats

The effects of bilateral hippocampal aspiration lesions on later acquisition of eyeblink conditioning were examined in developing Long-Evans rat pups. Lesions on postnatal day (PND) 10 were followed by evaluation of trace eyeblink conditioning (Experiment 1) and delay eyeblink conditioning (Experiment 2) on PND 25. Pairings of a tone conditioned stimulus (CS) and periocular shock unconditioned stimulus (US, 100 ms) were presented in one of three conditioning paradigms: trace (380 ms CS, 500 ms trace interval, 880 ms interstimulus interval [ISI]), standard delay (380 ms CS, 280 ms ISI), or long delay (980 ms CS, 880 ms ISI). The results of two experiments indicated that hippocampal lesions impaired trace eyeblink conditioning more than either type of delay conditioning. In light of our previous work on the ontogeny of trace, delay, and long-delay eyeblink conditioning (Ivkovich, Paczkowski, & Stanton, 2000) showing that trace and long-delay eyeblink conditioning had similar ontogenetic profiles, the current data suggest that during ontogeny hippocampal maturation may be more important for the short-term memory component than for the long-ISI component of trace eyeblink conditioning. The late development of conditioning over long ISIs may depend on a separate process such as protracted development of cerebellar cortex.     

Through the looking glass: Sex differences in memory for self-facial poses

This study investigated recognition memory of photographs of the subject's own face. Male and female subjects were photographed as they projected sociable faces, trustworthy faces, and intelligent faces. After deciding which face of 10 best represented each characteristic, and judging which photograph best represented their “real self,” a recognition memory test of poses was given. Half of each sex were tested under intentional learning conditions and the remainder were tested under incidental learning conditions. Females demonstrated superior recognition memory of their own facial projections and, in particular, recalled photographs of their “real self” and “most sociable” self most easily. No differences were found between the two learning conditions. Subjects' recognition performance was not related to their confidence of judgments. The results were discussed in terms of sex differences and the role of self in memory.     

Multivariate relationships between measures of learning style and memory

Three self-report instruments assessing “learning style” were administered to 106 undergraduate students: the Inventory of Learning Processes, the Study Behavior Questionnaire, and the Learning Style Inventory. Performance measures on word list and prose learning tasks were also obtained using both immediate and delayed retention tests. Canonical correlation analysis of the pairs of learning style instruments indicated that there was a small to moderate amount of overlapped variance. Inspection of the canonical variates revealed that what overlap existed was generally due to a common factor related to the depth of processing conception of memory. No significant canonical correlations were obtained between any of the learning style instruments and word list retention measures. However, the Inventory of Learning Processes and the Learning Style Inventory each obtained one significant canonical correlation with the set of prose retention measures. There was little overlap between sets of retention measures derived separately from prose and word list tasks. The findings have implications concerning (a) the validity and equivalency of available self-report instruments assessing learning style, (b) the role of the learning task in studying individual differences in learning and memory processes, and (c) the assessment of “depth of processing” at the level of individual differences.     

Motivation and learning: Neurophysiological mechanisms in a “model” system

The neurophysiological mechanisms underlying behavioral motivation and associative learning are described in an invertebrate “model” system, the carnivorous marine mollusc Pleurobranchaea. Feeding motivation can be controlled via nutritional history and is represented centrally in the feeding motor network as a change in the balance of synaptic excitation and inhibition at the level of interneurons that initiate feeding behavior, i.e., feeding “command” interneurons. Associative learning, induced by avoidance conditioning of feeding behavior, manifests identically at the level of the command interneurons, but is distinguished from non-associative motivational changes by processes that occur in identified neurons and pathways presynaptic to the command interneurons. Motivation and learning are therefore linked mechanistically by convergent neurophysiological mechanisms at the level of central neurons that initiate behavior.     

Disentangling the course of epistemic development: parsing knowledge by epistemic content

Over the past three decades, research into the developmental course by means of which persons come to an increasingly mature conception of the knowing process has yielded an highly defracted picture. Despite some concert of opinion about the general bill of particulars, what remains deeply problematic is the increasingly radical disagreement that has arisen regarding the ages at which major milestones in the course of epistemic development are said to be reached. As a way of making some sense of these competing claims, it is argued that the emerging insight that knowledge is ineluctably shaped by those doing the knowing (i.e., that there is an unavoidable “world-to-mind direction of fit” (J.R. Searle, Intentionality: An Essay in the Philosophy of Mind, Cambridge University Press, Cambridge, 1983) between things in the world and the manner of their understanding) does not arrive in a single piece. Instead, as the data presented here help to illustrate, an appreciation of the constructed character of knowledge more commonly arrives piecemeal and at different ontogenetic moments, the times of which are governed by the place that different objects of knowledge occupy along an envisioned continuum of diverse epistemic contents. On this account, not all “facts of the matter” are ordinarily seen to occupy the same epistemic footing. Rather, some so-called facts are commonly understood to be of an “institutional” sort, where “representational” diversity is early expected and widely tolerated. By contrast, other objects of knowledge are imagined to be more like “brute” facts that, on some less mature readings, fully escape the clutches of subjective opinion. Viewed against the backcloth of this proposed continuum, a developmental sequence hypothesized according to which growing persons first come to view “institutional” facts as humanly constructed before subsequently coming to a similar view about presumptively “brute” facts. To test this hypothesis, 242 young persons were administered a paper and pencil measure of epistemic reasoning (the EDQ). Results strongly support the hypothesis that respondents understood the interpretive nature of beliefs about “institutional” facts at an earlier age than so-called “brute” facts.