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PubMed2002

Is implicit learning spared in amnesia? Rule abstraction and item familiarity in artificial grammar learning.

We examined implicit learning of an artificial grammar in amnesic and control participants. The "biconditional" grammar used to generate study and test strings allows two potential sources of judgements in artificial grammar learning to be unconfounded: participants could either learn the abstract biconditional rules or could learn about the distributional statistics of the surface elements (e.g. bigrams) composing the study items. Test strings varied these two sources orthogonally. We found no evidence of abstract rule learning either in the control or amnesic groups. In contrast, both groups learned about the surface elements and tended to call test strings "grammatical" when they were composed of familiar bigrams. However, this sensitivity to bigram familiarity was significantly reduced in the amnesic compared to the control group. The results challenge the claim that implicit learning is intact in amnesia.

Amnesia↗
PubMed2002

Nitric oxide/cGMP-mediated protein kinase A activation in the antennal lobes plays an important role in appetitive reflex habituation in the honeybee.

Habituation, a form of non-associative learning, is observed throughout the animal kingdom. However, in contrast to associative learning, little is known about the underlying molecular mechanisms. Using the appetitive proboscis extension reflex in honeybees, we show that the cAMP-dependent protein kinase A (PKA) in the antennal lobe (AL) is implicated in the graded decline of behavioral response during habituation. Repeated stimulation leads to a slow and gradual increase in PKA activity superimposed on a fast transient PKA activation induced by each stimulus. These temporally distinct components of PKA activation are pharmacologically dissectible and are restricted to the AL on the stimulated side. Whereas the transient PKA activation induced by each stimulus requires monoaminergic transmission, the slow component of PKA activation is mediated by the nitric oxide (NO)/cGMP system. Local manipulation of the slow component of PKA activation in single ALs specifically interferes with the dynamic of habituation on the corresponding side. Our results provide strong evidence that NO/cGMP-mediated PKA activation in each AL contributes to temporal signal integration during habituation. Dishabituation by a sensory stimulus or spontaneous recovery from habituation does not require the PKA cascade. This provides evidence that the mechanisms underlying dishabituation and spontaneous recovery differ from those underlying temporal signal integration during habituation of the proboscis extension response.

Animals↗
PubMed2005

Adaptation to visuomotor transformations: consolidation, interference, and forgetting.

The paradigm task A-->task B-->task A, which varies the time interval between task A and task B, has been used extensively to investigate the consolidation of motor memory. Consolidation is defined as resistance to retrograde interference (interference by task B on initial learning of task A). Consolidation has been demonstrated for simple skills, motor sequencing, and learning of force fields. In contrast, evidence to date suggests that visuomotor learning does not consolidate. We have shown previously that adaptation to a 30 degrees screen-cursor rotation is faster and more complete on relearning 24 hr later. This improvement is prevented if a 30 degrees counter-rotation is learned 5 min after the original rotation. Here, we sought to identify conditions under which rotation learning becomes resistant to interference by a counter-rotation. In experiment 1, we found that interference persists even when the counter-rotation is learned 24 hr after the initial rotation. In experiment 2, we removed potential anterograde interference (interference by task B on relearning of task A) by introducing washout blocks before all of the learning blocks. In contrast to experiment 1, we found resistance to interference (i.e., consolidation) when the counter-rotation was learned after 24 hr but not after 5 min. In experiment 3, we doubled the amount of initial rotation learning and found resistance to interference even after 5 min. Our results suggest that persistent interference is attributable to anterograde effects on memory retrieval. When anterograde effects are removed, rotation learning consolidates both over time and with increased initial training.

Adaptation, Physiological↗
PubMed2004

Bilateral lesion of the cerebellar-dentate nucleus impairs egocentric sequential learning but not egocentric navigation in the rat.

The involvement of the cerebellum in procedural learning is demonstrated in visuomotor-sequence tasks, as lesion of this area impedes the acquisition of new sequences. Likewise, the lateral cerebellum appears to be involved in the acquisition of new sequences, but not in the execution of learned sequences. In contrast, the dentate nucleus participates only in the execution of learned visuomotor sequences. In previous studies, disruption of the procedural elements of spatial navigation following cerebellar or dentate lesions has been reported. However, as praxic strategies (egocentric learning) are included in the procedural elements of the navigation, the participation of the cerebellar-dentate nucleus in egocentric procedural learning processes has not been evaluated. Therefore, using colchicine, bilateral lesions were made in the cerebellar-dentate nucleus of Sprague-Dawley rats, and these rats were given two tasks: egocentric-based motor sequence learning in the radial maze and egocentric navigation in the Morris water maze. The lesioned rats were unable to use the sequential information in the short term and showed delayed long-term acquisition, which was probably due to the inability to detect the sequence. No effects on the egocentric navigation task were observed. Our results indicate that the cerebellar-dentate nucleus is involved in the detection of egocentric sequential information but not in the use of this information in the navigation process. Further, they show differential involvement of the cerebellar-dentate nucleus in the execution of learned visuomotor sequences, as the dentate lesion disrupted the acquisition of new egocentric-motor-based sequences.

Analysis of Variance↗
PubMed1990

Contrast and accentuation effects in category learning.

This study examines the accentuation of perceived intercategory differences. In Experiment 1, 2 sets of trait adjectives were presented--a neutral set and a set of either favorable traits or unfavorable traits. Ss estimated the mean favorability of each set. The mean favorability of the neutral set was then increased or decreased by adding new traits. As predicted, the estimated mean favorability of the neutral set changed more when the set became more distinct from a contextual set than when it became more similar. In Experiment 2, estimated category means were displaced away from each other (contrast effect), and they moved even farther apart when new information increased the variability of trait favorability (accentuation effect). This change was illusory because the actual category means remained constant. Experiment 3, in which trait adjectives described members of 2 novel groups, replicated Experiment 2. The relevance of contrast and accentuation effects to the development and maintenance of differentiated intergroup perceptions is discussed.

Adult↗
PubMed1988

Acquiring lexical contrast: the case of bring-take learning.

Production of the deictic verbs bring and take was evaluated among 88 normally functioning children (grades K-6). Theoretical approaches and assumptions concerning a working definition of word mastery were contrasted and found to influence (a) the evaluative scheme chosen to assess lexical knowledge and (b) conclusions concerning the development of lexical contrast. Results, which revealed a developmental order unlike that reported elsewhere, are related to the broad issue of interpretation of lexical overextension behavior. A model of antonym learning is proposed that assigns a prepotent role to the second-to-emerge term in a contrastive pair.

Child↗
PubMed2004

Contributions of the anterior forebrain pathway to vocal plasticity.

The anterior forebrain pathway (AFP) is a basal ganglia-dorsal forebrain circuit that is prominent specifically in birds that learn to sing. This circuit is interconnected with the song motor pathway, is active during song production, and contains neurons that are selective for the sound of the bird's own song, suggesting an important role for the AFP in vocal behavior. However, interruption of the AFP by lesions in adult birds has little overt effect on the production of learned song. In contrast, lesions in juvenile birds prevent the normal progression of song learning. Moreover, lesions in adults, while not disrupting production, can prevent experience-dependent plasticity of song. Such data implicate the AFP specifically in song learning and vocal plasticity. This chapter reviews some of the experimental evidence supporting a role for the AFP in these processes and discusses potential instructive and permissive functions of the AFP in vocal plasticity.

Animals↗
PubMed2001

Discriminating contrast discontinuities: asymmetries, dipper functions, and perceptual learning.

In a visual search task, a target has to be found among distractors. For two given elements A and B, the search difficulty can depend on which of the two elements is defined as the target, a phenomenon called search asymmetry. Here, we study to what degree an element's ability to 'win' in a search asymmetry depends on its absolute contrast (first-stage signal) and to what degree it depends on its contrast difference from the background (second-stage signal). One quadrant contained a target texture (2 x 2 Gabor patches of contrast c(tg)), and the other three quadrants contained distractor textures (2 x 2 Gabor patches of contrast c(dt)). These four 'foreground textures' were embedded in a background texture consisting of patches with contrast c(bg). The task was to identify which quadrant contained the target. Quadrants are referred to as increments (foreground contrast c(fg)>c(bg)), or decrements (c(fg)<c(bg)). We found that the second-stage signal determines which element wins the performance asymmetry, i.e. it is easier to find strong increments (decrements) among weak increments (decrements) than vice versa. A comparison of our data with the prediction of the independent-processing model [Vision Res. 40 (2000) 2677] shows that the observed performance asymmetries are in general too large to be attributed to noise differences alone. Rather, asymmetries might reflect a global competition between salient elements. Moreover, performance asymmetries can reverse during practice. We characterize a dipper-shaped nonlinearity on the second stage: discrimination of increment (decrement) signals x and x+Delta x first improves for increasing x, and then deteriorates.

Contrast Sensitivity↗
PubMed1998

The effects of MK-801 on spatial working memory and within-session spatial learning.

The present study investigated the effects of the NMDA channel blocker MK-801 (0.05, 0.10, and 0.15 mg/kg) on a task that allows for the assessment of both spatial working memory and within-session spatial learning. During the first trial of each day, subjects were shown the spatial location of a food reward on a six-arm radial-arm maze. During nine subsequent free-choice trials, subjects were reinforced for returning to that same spatial location. The location of the food reward varied across days. Thus, choosing correctly on any given trial required subjects to remember where food had been received during the previous trials of that day. The effects of MK-801 on working memory were assessed by analyzing the overall number of errors committed during the nine free-choice trials of each day. The effects of MK-801 on within-session learning were assessed by comparing the number of errors committed during the first three trials of each day to the number of errors committed during the last three trials of each day. Only the highest dose of MK-801 tested (0.15 mg/kg) impaired spatial working memory. No dose of MK-801 impaired the ability of subjects to acquire spatial information within a given session. The failure of MK-801 to impair within-session spatial learning stands in contrast to the well-known effects of MK-801 on spatial learning measured across days. Thus, when coupled with previous research, the findings of the present study further suggest that the NMDA receptor plays a role in the long-term, but not short-term, storage of spatial information.

Adaptation, Psychological↗
PubMed1975

An analysis of short-term visual memory in the monkey.

Visual memory in monkeys was examined under four different conditions, each with a separate group. In all conditions, the delay between sample and choice was 10 sec, and the delay between trials was 30 sec. The procedural differences were matching or nonmatching with the same two objects presented repeatedly and matching or nonmatching with trial-unique objects. With the customary repetitive stimuli, whether in matching or nonmatching, most monkeys either required prolonged training to solve the problem (over 40 sessions) or failed to solve it, corroborating the learning difficulties reported earlier by others. With trial-unique stimuli, by contrast, most monkeys learned quickly (matching, under 20 sessions; nonmatching, under 5 sessions). Furthermore, in nonmatching with trial-unique stimuli, scores averaged 80% correct in the first session, even though the monkeys were experimentally naive. The results indicate that recognition of a stimulus as familiar or novel is highly developed in monkeys, and that their difficulty with the customary nonspatial visual memory tasks stems from a retardation in noticing and using the mnemonic cue of recovery of presentation. Evidence is presented that this difficulty can be overcome, however, by a simple training procedure that exploits their proficiency at distinguishing familiar from novel stimuli.

Animals↗
PubMed1999

Comparison and contrast as a mechanism of perceptual learning?

In a series of flavour aversion experiments, rats received different schedules of pre-exposure to two compound flavours (AX and BX). Discrimination between them was assessed by establishing an aversion to AX and measuring generalization of this aversion to BX. Experiment 1 demonstrated that alternating pre-exposure to AX and BX resulted in less generalization than did blocked exposure, where animals received all exposure to AX before exposure to BX (or vice versa). This difference was not accompanied by any difference in the strength of the aversion conditioned to the common X element. Varying the interval between exposure to AX and BX in the alternating condition from a minute or two to several hours had no effect on generalization. However, Experiments 2 and 3 showed that when the interval between exposure to AX and that to BX was reduced to zero sec, the alternating schedule increased generalization between AX and BX. In this case, the increase in generalization was accompanied by an increase in the strength of the aversion conditioned to X.

Animals↗
PubMed1968

Discrimination learning, the peak shift, and behavioral contrast.

A discrimination between two successively alternating stimuli was trained under conditions that maintained equal frequencies of reinforcement in the presence of each of the discriminative stimuli (S1 and S2) but that also reduced the rate of responding to S2. These conditions included a multiple variable-interval differential-reinforcement-of-low-rate schedule and a multiple variable-interval variable-interval schedule in which responses to S2 were punished. Whenever the rate of responding to S2 was reduced, rate of responding to S1 (behavioral contrast) increased, and the peak of a subsequently obtained generalization gradient did not occur at the expected location (between S1 and S2) but was displaced away from S2, below S1. Discrimination training in which the frequencies of reinforcement earned in S1 and S2 were not equal (variable-interval 1-min variable-interval 5-min training) produced contrast and the peak shift only if the rate of responding to S2 had been reduced, as after non-differential reinforcement in which variable-interval 1-min schedules were correlated with S1 and with S2. It was concluded that a sufficient condition for the occurrence of behavioral contrast and the peak shift was reduction of the rate of responding to one of two alternating discriminative stimuli and that a peak shift will occur only if contrast had occurred during discrimination training.

Journal Article↗
PubMed1993

Cross-modality matching in memory psychophysics: brightness and loudness.

Performance of subjects in tasks involving estimation of remembered magnitude and cross-modality matching of remembered magnitude for brightness and loudness stimuli was examined in two experiments. Subjects first learned nonsense syllable names associated with exemplars of five levels of brightness and exemplars of five levels of loudness. The stimuli were then removed and one of the nonsense syllable names was given by the experimenter. The subject formed an image of what the stimulus denoted by that name looked or sounded like and gave a judgment of remembered magnitude of that stimulus based upon the intensity portrayed in the image. In Exp. 1 subjects also completed a cross-modality matching task in which a stimulus in one dimension was shown, and subjects then estimated the magnitude that a stimulus in the other dimension would have to possess to match the intensity of the perceived stimulus. Performance was compared with that of a perceptual control group. In Exp. 2 subjects also completed a cross-modality matching task in which they were given the nonsense syllable name of a stimulus from one dimension, formed a vivid image of what the stimulus denoted by that name looked or sounded like, formed an image of a stimulus from the other dimension that possessed the same portrayed intensity as the named stimulus from the first dimension, and then estimated the intensity of the second (unnamed) stimulus. The power function offers an appropriate description of the responses on both the remembered magnitude and the cross-modality matching tasks. Implications for theories of imagery and psychophysics are discussed.

Adult↗
PubMed1994

Young children's concept of color and its relation to the acquisition of color words.

Many children experience great difficulty in learning their first color word. In contrast, once children have learned 1 color word, they learn additional color words more easily. This striking fact rises the question of whether children who do not know color words have conceptual color categories capable of supporting inferences about word meaning. In 3 experiments 2-year-olds were provided with tasks that required them to base inferences on color or to map things onto color. Half the children comprehended at least 1 color word, and the remaining children comprehended none. In all experiments, the children in both groups succeeded on the color tasks. It was argued that children who do not know color words have the conceptual foundation necessary to base inferences on color but have specific constraints against basing inferences about word meaning on color.

Child Development↗
PubMed2006

Perceptual learning of motion direction discrimination in fovea: separable mechanisms.

Dosher and Lu (1998) [Perceptual learning reflects external noise filtering and internal noise reduction through channel reweighting. Proceedings of the National Academy of Sciences of the United States of America, 95 (23), 13988-13993.] proposed three mechanisms of perceptual learning: stimulus enhancement, external noise exclusion, and multiplicative noise reduction. In this study, we used pre-training as a manipulation to evaluate the separability of these mechanisms as a key test of the theoretical framework. Observers were trained in identifying the motion direction of a moving sine-wave grating in fovea with varying amount of superimposed external noise across trials, after receiving no pre-training, pre-training in high external noise, or pre-training in zero external noise in the same task. We found: (1) Without pre-training, perceptual learning significantly reduced contrast thresholds by about the same amount across all the external noise levels. (2) Both types of pre-training significantly reduced contrast thresholds in the corresponding conditions. (3) Pre-training in high external noise greatly reduced subsequent learning in high external noise, accounting for 64.6% of the total (pre-training + subsequent) improvements in that condition. On the other hand, the amount of subsequent learning in low external noise conditions was essentially the same as the total (pre-training + subsequent) amount of improvements in high external noise, suggesting that pre-training in high external noise had mostly only improved performance in noisy displays. (4) Pre-training in zero external noise practically eliminated or left very little additional learning in all the external noise conditions. We concluded that the two mechanisms of perceptual learning, stimulus enhancement, and external noise exclusion, can be trained independently in motion direction discrimination in fovea; training in low noise suffices to improve observer performance over all the external noise conditions.

Adult↗