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PubMed1979

Acquisition of prerequisites to conservation by macaques.

Through a progressive series of learning sets, two rhesus macaques were trained to discriminate transformations that produce change of substance from other transformations and manipulations. Several tests were administered to assess the generalization of this discrimination to a variety of objects and shapes and to assess the effects, if any, of size cues, experimenter familiarity, and various methods to problem presentation. After training was completed, performance was not greatly affected by differences in problems and presentations. The results of these experiments suggest that monkeys can acquire this prerequisite for substance conservation as a result of learning set training.

Animals↗
PubMed1979

Influence of acoustic experience on the ontogeny of frequency generalization gradients in the chicken.

The role of auditory experience in the ontogeny of perceptual coding was investigated in hatching chickens. In Experiment 1, auditory frequency generalization gradients were determined by using a habituation-generalization paradigm and an orienting response. One-day and 3-4 day chicks were habituated to 800-Hz tones and then tested at five frequencies ranging from 800 to 1,000 Hz. One-day chicks displayed reliably flatter generalization gradients than 3-4-day chicks. In Experiment 2 an auditory deprivation method is described in which an ear impression compound was injected into the external ear. This method (a) is fully calibrated and provides approximately 40 dB of attenuation across a .125- to 4.0-kHz range, (b) appears to be fully reversible, and (c) is applicable prior to normal auditory experience as well as at subsequent stages. In Experiment 3, this method was used to investigate the effects of auditory deprivation on the "perceptual sharpening" described in Experimental 1. Chicks were deprived from Embryonic Day 18 1/2 to 3-4 days posthatch, at which time normal, deprived, and sham-operated chicks were tested as in Experiment 1. The generalization gradients of the deprived chicks were significantly flatter than those of the 3-4 day normal and sham-operated chicks and were similar to those of 1-day chicks. This effect cannot be attributed to (a) operative procedures, (b) changes in auditory thresholds, or (c) changes in response rate with age or condition. Thus the perceptual sharpening normally occurring between 1 and 3-4 days posthatch fails to occur during that time in the absence of a normal acoustic environment.

Acoustic Stimulation↗
PubMed1991

Forgetting and the mirror effect in recognition memory: concentering of underlying distributions.

The mirror effect is a strong regularity in recognition memory: If there are two conditions, A and B, with A giving higher recognition accuracy, then old items in A are recognized as old better than old items in B, and also new items in A are recognized as new better than new items in B. The mirror effect is explained by attention/likelihood theory, which also makes several new, counterintuitive predictions. One is that any variable, such as forgetting, that affects recognition changes the responses to new as well as old stimuli. In terms of underlying distributions, forgetting produces concentering, the bilateral movement of distributions, both new (noise) and old (signal), toward a midpoint. Data from two forced-choice experiments are reported that support the prediction of concentering and other predictions drawn from the theory. It is argued that current theories of memory, which are strength theories, cannot handle these regularities.

Attention↗
PubMed2000

Thirty categorization results in search of a model.

One category structure dominated in the shift toward exemplar-based theories of categorization. Given the theoretical burden on this category structure, the authors reanalyzed 30 of its uses over 20 years in 8 articles. The authors suggest 4 conclusions. (a) This category structure may encourage exemplar-memorization processes because of its poor structure, the learning difficulties it causes, and its small, memorizable exemplar sets. Its results may only generalize narrowly. (b) Exemplar models have an advantage in fitting these 30 data sets only because they reproduce a performance advantage for training items. Other models fit equally well if granted this capacity. (c) A simpler exemplar process than assumed by exemplar models suffices to explain these data sets. (d) An important qualitative result predicted by exemplar theory is not found overall and possibly should not even be expected. The authors conclude that the data produced by this category structure do not clearly support exemplar theory.

Concept Formation↗
PubMed2002

Adaptive categorization in unsupervised learning.

In 3 experiments, the authors provide evidence for a distinct category-invention process in unsupervised (discovery) learning and set forth a method for observing and investigating that process. In the 1st 2 experiments, the sequencing of unlabeled training instances strongly affected participants' ability to discover patterns (categories) across those instances. In the 3rd experiment, providing diagnostic labels helped participants discover categories and improved learning even for instance sequences that were unlearnable in the earlier experiments. These results are incompatible with models that assume that people learn by incrementally tracking correlations between individual features; instead, they suggest that learners in this study used expectation failure as a trigger to invent distinct categories to represent patterns in the stimuli. The results are explained in terms of J. R. Anderson's (1990, 1991) rational model of categorization, and extensions of this analysis for real-world learning are discussed.

Analysis of Variance↗
PubMed1997

Chorda tympani nerve transection disrupts taste aversion learning to potassium chloride, but not sodium chloride.

In Experiment 1, rats with chorda tympani nerve transection (CTX) acquired a LiCl-conditioned taste aversion to 0.1 M NaCl at the same rate as controls. After 3 conditioning trials, the aversion generalized to 0.03 and 0.3 M NaCl, but did not generalize to KCI (0.03, 0.1, and 0.3 M), in either the sham or CTX group. In Experiment 2, the sham group, but not the CTX group, formed an aversion to 0.1 M KCI after 1 trial. The CTX rats did form a moderate aversion after 2 conditioning trials. Following the 3rd trial, the CTX group did not suppress licking to 0.03 or 0.3 M KCI or any concentration of NaCl in relation to controls. Although there is strong evidence that CTX affects NaCl taste perception, these findings indicate that, under certain conditions, rats can nonetheless distinguish NaCl from KCI after such neurotomy. Moreover, CTX appears to have a substantial effect on the perceived intensity of KCl.

Animals↗
PubMed1998

The dorsal hippocampus is essential for context discrimination but not for contextual conditioning.

The authors describe how (a) the timing of hippocampal lesions and (b) the behavioral-representational demands of the task affect the requirement for the hippocampus in contextual fear conditioning. Post- but not pretraining lesions of the hippocampus greatly reduced contextual fear conditioning. In contrast, pretraining lesions of the hippocampus abolished context discrimination, a procedure in which mice are trained to discriminate between 2 similar chambers (shock context vs. no-shock context). Whereas either contextual- or cue-based strategies can be used to recognize an aversive context, discrimination between similar contexts is optimally acquired by contextual (hippocampal)-based strategies. In keeping with the lesion results, Nf1(+/-)/Nmdar1(+/-) mutant mice, which have spatial learning deficits, are impaired in context discrimination but not in contextual conditioning. Together, these data dissociate hippocampal and nonhippocampal contributions to contextual conditioning, and they provide direct evidence that the hippocampus plays an essential role in the processing of contextual stimuli.

Analysis of Variance↗
PubMed2001

Selective loss of cholinergic neurons projecting to the olfactory system increases perceptual generalization between similar, but not dissimilar, odorants.

The neuromodulator acetylcholine is thought to modulate information processing in the olfactory system. The authors used 192 IgG-saporin, a lesioning agent selective for basal forebrain cholinergic neurons, to determine whether selective lesions of cholinergic neurons projecting to the olfactory bulb and cortex affect odor perception in rats. Lesioned and sham-operated rats were tested in an olfactory generalization paradigm with sets of chemically related odorants (n-aliphatic aldehydes, acids, and alcohols). Lesioned rats generalized more between chemically similar odorants but did not differ from controls in their response to chemically unrelated odorants or in acquisition of the conditioned odor. Results show that cholinergic inputs to the olfactory system influence perceptual qualities of odorants and confirm predictions made by computational models of this system.

Acetylcholine↗
PubMed2002

Behavioral models of odor similarity.

Carbon chain length in several classes of straight-chain aliphatic odorants has been proposed as a model axis of similarity for olfactory research, on the basis of successes of studies in insect and vertebrate species. To assess the influence of task on measured perceptual similarities among odorants and to demonstrate that the systematic similarities observed within homologous odorant series are not task specific, the authors compare 3 different behavioral paradigms for rats (olfactory habituation, generalization, and discrimination). Although overall patterns of odorant similarity are consistent across all 3 of these paradigms, both quantitative measurements of perceptual similarity and comparability with 2-deoxyglucose imaging data from the olfactory bulb are dependent on the specific behavioral tasks used. Thus, behavioral indices of perceptual similarity are affected by task parameters such as learning and reward associations.

Animals↗
PubMed1984

Neural lateralization of vocalizations by Japanese macaques: communicative significance is more important than acoustic structure.

The study was designed to determine whether the neural lateralization of vocal perception in Japanese macaques depends on the acoustic properties of the calls used or their communicative significance. Four monkeys--two Japanese macaques and two comparison macaques--were trained to discriminate among monaurally presented exemplars of two classes of vocalizations from the Japanese macaque's repertoire. Once the subjects mastered the discrimination, they performed at equivalent accuracy levels for 150 sessions. However, during this time the Japanese monkeys showed a right ear performance advantage, whereas the comparison monkeys showed no ear advantage. In order to assess whether the comparison and Japanese monkeys were attending to the same acoustic cue when performing the discrimination, a generalization test was conducted with 27 novel vocalizations. The individual monkeys' generalization gradients were highly similar and revealed that all subjects were in fact listening to the same feature of the calls. These findings, coupled with the fact that the calls were of biological significance to the Japanese monkeys alone, suggest that the laterality effect is related, in some fashion, to the communicative valence of the signals rather than their purely physical characteristics.

Animals↗
PubMed1998

Response latencies for false memories: gist-based processes in normal aging.

Three experiments have demonstrated that age-related increases in both probability and speed of false recognitions for word lists depended on the use of a gist-based memory strategy. When test conditions promoted a gist strategy, both younger and older participants were as likely to falsely recognize a thematically associated lure as to correctly recognize a studied item, and both groups were equally fast in making these decisions. However, when test conditions deemphasized a gist-based strategy, older adults were more likely than younger adults, and faster, to falsely recognize both strong and weakly associated lures. These findings suggest an age-related increase in reliance on gist-based processing that may underlie age differences in false memory.

Adult↗
PubMed1994

Rule-plus-exception model of classification learning.

The authors propose a rule-plus-exception model (RULEX) of classification learning. According to RULEX, people learn to classify objects by forming simple logical rules and remembering occasional exceptions to those rules. Because the learning process in RULEX is stochastic, the model predicts that individual Ss will vary greatly in the particular rules that are formed and the exceptions that are stored. Averaged classification data are presumed to represent mixtures of these highly idiosyncratic rules and exceptions. RULEX accounts for numerous fundamental classification phenomena, including prototype and specific exemplar effects, sensitivity to correlational information, difficulty of learning linearly separable versus nonlinearly separable categories, selective attention effects, and difficulty of learning concepts with rules of differing complexity. RULEX also predicts distributions of generalization patterns observed at the individual subject level.

Adult↗
PubMed1990

Neural nets for generalization and classification: comment on Staddon and Reid (1990)

The neural net model of Staddon and Reid (1990) explains exponential and Gaussian generalization gradients in the same way as the diffusion model of Shepard (1958). The "cognitive" generalization theory of Shepard (1987), which also has been implemented as a connectionist network, goes beyond both of these models in accounting for classification learning.

Brain↗
PubMed2005

Effects of backward speech and speaker variability in language discrimination by rats.

Human infants use prosodic cues present in speech to extract language regularities, and it has been suggested that this capacity is anchored in more general mechanisms that are shared across mammals. This study explores the extent to which rats can generalize prosodic cues that have been extracted from a training corpus to new sentences and how this discrimination process is affected by the normalization of the sentences when multiple speakers are introduced. Conditions 1 and 2 show rats' abilities to use prosodic cues present in speech, allowing them to discriminate between sentences not previously heard. But this discrimination is not possible when sentences are played backward. Conditions 3 and 4 show that language discrimination by rats is also taxed by the process of speaker normalization. These findings have remarkable parallels with data from human adults, human newborns, and cotton-top tamarins. Implications for speech perception by humans are discussed.

Animals↗
PubMed2003

Development of categorization and reasoning in the natural world: novices to experts, naive similarity to ecological knowledge.

Two experiments investigate the role of similarity and causal-ecological knowledge in expert and novice categorization and reasoning. In Experiment 1, university undergraduates and commercial fishermen sorted marine creatures into groups; although there was substantial agreement, novices sorted largely on the basis of appearance, whereas experts often cited commercial, ecological, or behavioral factors, and systematically subdivided fish on the basis of ecological niche. In Experiment 2, experts and novices were asked to generalize a blank property or novel disease from a pair of marine creatures. Novices relied on similarity to guide generalizations. Experts used similarity to reason about blank properties but ecological relations to reason about diseases. Expertise appears to involve knowledge of multiple relations among entities and context-sensitive application of those relations.

Cognition↗
PubMed1988

Effects of poisoning on predatory and ingestive behavior toward artificial prey in rats (Rattus norvegicus).

Ingestion of novel prey by vertebrate predators that is followed by illness typically decreases the predators' eating the prey more readily than their pursuing or killing it. We used artificial prey-food items (rolling ball bearings that predicted food pellets) to model and extend this finding in laboratory rats. During daily experimental sessions presentations of a novel bearing-food combination were intermixed with presentations of a familiar bearing-food combination. The poisoned animals received lithium chloride injections after each session. Experiment 1a showed that: (a) Poisoning markedly decreased ingestion of the novel food without decreasing the frequency of contact (nose, seize, carry, or chew) with the novel bearing predicting that food. (b) However, poisoning did significantly decrease the average duration of contact with the novel bearing. (c) Poisoning did not decrease behavior toward the familiar food and bearing. Experiment 1b showed that after moderate exposure to pairings of the novel food and bearing, poisoning decreased behavior toward both novel and familiar food and bearings. The results indicate that important aspects of predation can be simulated and examined in the laboratory by using artificial prey-food items. These results also support the conclusions that predatory behavior and ingestion reflect separable modes of behavior and that the presence of novel prey interferes with the generalization of poisoning effects to familiar prey.

Animals↗
PubMed1990

Acoustic classification of alarm calls by vervet monkeys (Cercopithecus aethiops) and humans (Homo sapiens): II. Synthetic calls.

In 2 experiments classification of synthetic versions of species-typical snake and eagle alarm calls by vervet monkeys (Cercopithecus aethiops) and human (Homo sapiens) control subjects was investigated. In a 2-choice, operant-conditioning-based procedure, this work followed up acoustic analyses that had used various digitally based algorithms (Owren & Bernacki, 1988). All subjects were first tested with alarm-call replicas that were based on analysis data. These models were classified in the same manner as natural stimuli, which verified the appropriateness of the acoustic characterizations. Synthetic stimuli were then presented to test the importance of specific acoustic cues. Spectral patterning was found to be the most salient cue for classification by the monkeys, whereas results from the human subjects were mixed. Implications for the study of nonhuman primate vocalizations and Lieberman's (1984) theory of speech evolution are discussed.

Adult↗