Temporal Discrimination Learning Research Articles

Spectral plasticity in monkey primary auditory cortex limits performance generalization in a temporal discrimination task.

Auditory experience and behavioral training can modify perceptual performance. However, the consequences of temporal perceptual learning for temporal and spectral neural processing remain unclear. Specifically, the attributes of neural plasticity that underlie task generalization in behavioral performance remain uncertain. To assess the relationship between behavioral and neural plasticity, we evaluated neuronal temporal processing and spectral tuning in primary auditory cortex (AI) of anesthetized owl monkeys trained to discriminate increases in the envelope frequency (e.g., 4-Hz standard vs. >5-Hz targets) of sinusoidally amplitude-modulated (SAM) 1-kHz or 2-kHz carriers. Behavioral and neuronal performance generalization was evaluated for carriers ranging from 0.5 kHz to 8 kHz. Psychophysical thresholds revealed high SAM discrimination acuity for carriers from one octave below to ∼0.6 octave above the trained carrier frequency. However, generalization of SAM discrimination learning progressively declined for carrier frequencies >0.6 octave above the trained carrier frequency. Neural responses in AI showed that SAM discrimination training resulted in 1) increases in temporal modulation preference, especially at carriers close to the trained frequency, 2) narrowing of spectral tuning for neurons with characteristic frequencies near the trained carrier frequency, potentially limiting spectral generalization of temporal training effects, and 3) enhancement of firing-rate contrast for rewarded versus nonrewarded SAM frequencies, providing a potential cue for behavioral temporal discrimination near the trained carrier frequency. Our findings suggest that temporal training at a specific spectral location sharpens local frequency tuning, thus, confining the training effects to a narrow frequency range and limiting generalization of temporal discrimination learning across a wider frequency range.NEW & NOTEWORTHY Monkeys' ability to generalize amplitude modulation discrimination to nontrained carriers was limited to one octave below and 0.6 octave above the trained carrier frequency. Asymmetric generalization was paralleled by sharpening in cortical spectral tuning and enhanced firing-rate contrast between rewarded and nonrewarded SAM stimuli at carriers near the trained frequency. The spectral content of the training stimulus specified spectral and temporal plasticity that may provide a neural substrate for limitations in generalization of temporal discrimination learning.

Contribution of the retrosplenial cortex to temporal discrimination learning.

The retrosplenial cortex (RSC) has an important role in contextual learning and memory. While the majority of experiments have focused on the physical context, the present study asked whether the RSC is involved in processing the temporal context. Rats were trained in a temporal discrimination procedure where the duration of the intertrial interval (ITI) signaled whether or not the next tone conditioned stimulus would be paired with food pellet reinforcement. When the tone was presented after a 16-min ITI it was reinforced, but when it was presented after a 4-min ITI it was not. Rats demonstrated successful discrimination in this procedure by responding more to the tone on reinforced trials than on non-reinforced trials. Pre-training electrolytic lesions of the RSC attenuated acquisition of the temporal discrimination. The results are the first to demonstrate a role for the RSC in processing temporal information and in turn extend the role of the RSC beyond the physical context to now include the temporal context.

Asymmetrical generalization of conditioning and extinction from compound to element and element to compound.

Four appetitive conditioning experiments studied generalization between compound conditional stimuli (AB) and their elements (e.g., A or B). In Experiments 1 and 2, rats received conditioning with A and AB, and then extinction with either A or AB. During subsequent testing, there was more generalization of extinction (nonresponding) from the compound (AB) to the element (A) than from the element (A) to the compound (AB). This asymmetry was consistent with earlier results involving temporal discrimination learning in which short and long temporal intervals played the roles of A and AB. In Experiment 3, rats received conditioning with either A or AB, and then testing with A and AB. Consistent with elemental models of conditioning, there was more generalization of conditioned responding from A to AB than from AB to A. Experiment 4 found that these asymmetries in the generalization of extinction (Experiments 1 and 2) and conditioning (Experiment 3) both contribute to the feature-positive effect. Overall, the parallel between the current findings and previous results with temporal discrimination learning supports an associative analysis of interval timing. Implications for elemental and configural theories of conditioning and generalization are also discussed.

Temporal discrimination learning for treatment of gait dysfunction in Parkinson’s disease: a feasibility study using single subject design

Temporal discrimination learning for treatment of gait dysfunction in Parkinson’s disease: a feasibility study using single subject design

Temporal discrimination learning for treatment of gait dysfunction in Parkinson’s disease: a feasibility study using single subject design

Freezing of gait in Parkinson’s disease may be attributed to dysfunctional neural timing that alters stride time variability. This study investigated the feasibility of a five-day perceptual timing training program using an auditory interval discrimination task to reduce stride time variability in Parkinson’s disease. Results showed that training produced an increase in time-discrimination acuity in a Parkinson’s disease patient, followed by a decrease in stride time variability. Effects persisted six weeks after training. No learningtransfer effects were found in a patient trained in a pitch discrimination task. In conclusion, interval discrimination training may reduce temporal gait irregularities in Parkinson’s disease.

Intertrial interval as a contextual stimulus: further analysis of a novel asymmetry in temporal discrimination learning.

Four experiments investigated discrimination learning when the duration of the intertrial interval (ITI) signaled whether or not the next conditional stimulus (CS) would be paired with food pellets. Rats received presentations of a 10-s CS separated half the time by long ITIs and half the time by short ITIs. When the long ITI signaled that the CS would be reinforced and the short interval signaled that it would not be (Long+/Short-), rats learned the discrimination readily. However, when the short ITI signaled that the CS would be reinforced and the long interval signaled that it would not (Short+/Long-), discrimination learning was much slower. Experiment 1 compared Long+/Short- and Short+/Long- discrimination learning with 16-min/4-min or 4-min/1-min ITI combinations. Experiment 2 found no evidence that Short+/Long- learning is inferior because the temporal cue corresponding to the short interval is ambiguous. Experiment 3 found no evidence that Short+/Long- learning is poor because the end of a long ITI signals a substantial reduction in delay to the next reinforcer. Long+/Short- learning may be faster than Short+/Long-because elapsing time involves exposure to a sequence of hypothetical stimulus elements (e.g., A then B), and feature-positive discriminations (AB+/A-) are learned quicker than feature-negative discriminations (A+/AB-). Consistent with this view, Experiment 4 found a robust feature-positive effect when sequentially presented CSs played the role of elements A and B.

Interstimulus interval as a discriminative stimulus: Evidence of the generality of a novel asymmetry in temporal discrimination learning

Three appetitive conditioning experiments with rats examined temporal discrimination learning within Pavlovian conditioning trials. In all experiments, the duration of a feature white noise stimulus signaled whether or not a subsequent 10-s target tone would be reinforced. In Experiment 1, the feature durations were 4 and 1min. For one group of rats (Group 4+/1-), 4min of noise signaled that the tone would be reinforced and 1min of noise signaled that the tone would not be reinforced. A second group (Group 1+/4-) was trained with the reverse contingency. The results showed a clear asymmetry in temporal discrimination learning: rats trained with 4+/1- (Long+/Short-) learned the discrimination readily (responding more in the tone on reinforced than on nonreinforced trials), whereas rats trained with 1+/4- (Short+/Long) did not. In Experiment 2, the feature durations were shortened to 60 and 15s. Due to strong excitatory conditioning of the 15-s feature, the reverse asymmetry was observed, with the Short+/Long- discrimination learned more readily than the Long+/Short- discrimination. However, Experiment 3 demonstrated that the original Long+/Short- advantage could be recovered while using 60- and 15-s feature durations if the excitatory conditioning of the feature was reduced by including nonreinforced feature trials. The results support previous research involving the timing of intertrial intervals and are consistent with the temporal elements hypothesis which holds that the passage of time is encoded as a series of hypothetical stimulus elements.

Somatosensory temporal discrimination learning generalizes to motor interval production

The present study investigated whether a common timing mechanism underlies the ability to analyze incoming sensory information and control outgoing motor commands. Participants were presented with two pairs of air puffs on the ventral surface of the right forearm. One pair (the standard interval) was separated by 500 ms on every trial for half of the participants (“500 group”) and 800 ms on every trial for the other half (“800 group”). The duration of the comparison interval was always longer but varied adaptively to determine discrimination thresholds. Participants indicated which of the two intervals was longer. Both groups performed two motor interval production tasks (pressing a button twice in succession with the right thumb) before and again after somatosensory training. The target inter-press interval was 500 ms in one task and 800 ms in the other. A critical feature of the design was that only one of the motor tasks for each of the groups shared temporal properties with the somatosensory discrimination task. The results showed that somatosensory discrimination learning generalizes to motor interval production when the two tasks share temporal properties. Specifically, the 500 group showed a greater reduction in motor timing variability on the 500 ms task than the 800 ms task, whereas the 800 group showed a greater reduction in motor timing variability on the 800 ms task than the 500 ms task. The possible neural basis of temporal learning generalization is discussed.

Temporal discrimination learning by pigeons

Memory for time by animals appears to undergo a systematic shortening. This so-called choose-short effect can be seen in a conditional temporal discrimination when a delay is inserted between the sample and comparison stimuli. We have proposed that this temporal shortening may result from a procedural artifact in which the delay appears similar to the intertrial interval and thus, produces an inadvertent ambiguity or 'instructional failure'. When this ambiguity is avoided by distinguishing the intertrial interval from the delay, as well as the samples from the delay, the temporal shortening effect and other asymmetries often disappear. By avoiding artifacts that can lead to a misinterpretation of results, we may understand better how animals represent time. An alternative procedure for studying temporal discriminations is with the psychophysical bisection procedure in which following conditional discrimination training, intermediate durations are presented and the point of subjective equality is determined. Research using the bisection procedure has shown that pigeons represent temporal durations not only as their absolute value but also relative to durations from which they must be discriminated. Using this procedure, we have also found that time passes subjectively slower when animals are required to respond to the to-be-timed stimulus.

Facilitating Effect of 15-Hz Repetitive Transcranial Magnetic Stimulation on Tactile Perceptual Learning

Recent neuroimaging studies have revealed that tactile perceptual learning can lead to substantial reorganizational changes of the brain. We report here for the first time that combining high-frequency (15 Hz) repetitive transcranial magnetic stimulation (rTMS) over the primary somatosensory cortex (SI) with tactile discrimination training is capable of facilitating operant perceptual learning. Most notably, increasing the excitability of SI by 15-Hz rTMS improved perceptual learning in spatial, but not in temporal, discrimination tasks. These findings give causal support to recent correlative data obtained by functional magnetic resonance imaging studies indicating a differential role of SI in spatial and temporal discrimination learning. The introduced combination of rTMS and tactile discrimination training may provide new therapeutical potentials in facilitating neuropsychological rehabilitation of functional deficits after lesions of the somatosensory cortex.

Temporal discrimination learning in severe amnesic patients reveals an alteration in the timing of eyeblink conditioned responses.

This study investigated whether the hippocampal system plays a modulatory role in the timing of conditioned responses (CRs) in eyeblink classical conditioning. Seven bitemporal amnesic patients and 7 controls were randomly presented 2 tone conditioned stimuli (CSs) that were individually paired with two different interstimulus intervals (ISIs) in a delay conditioning task. It was found that amnesic patients' CRs occurred significantly earlier than control participants' CRs at the longer ISI. Amnesic patients also produced significantly more nonadaptive CRs than did control participants, their level of acquisition was less than that of control participants after equating for ISI, and they did not show extinction with the longer ISI. These data suggest a role of the hippocampal system in controlling the precise timing of conditioned eyeblink responses and in acquiring and extinguishing responses within the context of a temporal discrimination task.

Temporal discrimination learning in severe amnesic patients reveals an alteration in the timing of eyeblink conditioned responses.

Temporal discrimination learning in severe amnesic patients reveals an alteration in the timing of eyeblink conditioned responses.

TEMPORAL DISCRIMINATION LEARNING OF OPERANT FEEDING IN GOLDFISH (CARASSIUS AURATUS)

Operant temporal discrimination learning was investigated in goldfish. In the first experiment, there was a fixed daily change in illumination. Eight subjects were trained to operate a lever that reinforced each press with food. The period during which responses were reinforced was then progressively reduced until it was 1 hr in every 24. The final 1-hr feeding schedule was maintained over 4 weeks. The feeding period commenced at the same time each day throughout. The food dispensers were then made inactive, and a period of extinction ensued for 6 days. The pattern of responding suggested that the fish were able to exhibit temporal discrimination in anticipation of feeding time. This pattern of responding persisted for a limited number of days during the extinction procedure. The second experiment produced evidence that operant temporal discrimination could develop under continuous illumination.

Absence of impairments in spatial and temporal discrimination learning in Lewis rats after chronic ethanol consumption

Many studies reported that chronic ethanol consumption leads to cognitive dysfunction in rodents. It has been suggested that the effects of chronic ethanol consumption resemble those of aging because of the behavioral and neurochemical similarities between the two processes. The present study examined the effects of a chronic ethanol treatment (20% aqueous solution) in Lewis rats on performance in three different tasks: the Morris spatial navigation task, a cone-field task, and a temporal discrimination task. Although an age-related deficit was found in water escape learning, chronic ethanol consumption did not affect the performance of adult and old rats. The results of this experiment were, however, not conclusive. No differences between old control and ethanol-treated rats were found for spatial (con-field task) and temporal discrimination learning. However, old ethanol-treated rats showed a transient tendency to perseverate in the temporal discrimination task. The present results are at variance with the generally found cognitive impairments after chronic ethanol consumption using aqueous solutions. It is suggested that the effects of ethanol could be related to strain of rat, task complexity, method of ethanol administering, and housing conditions and may explain the discrepancy between results.

Age-related changes in correlation between behavioral and biochemical parameters in lewis rats

This study evaluated aging by using a correlational analysis of behavior and biochemistry in young (4 months old) and old (24 months old) Lewis rats. The rats were subjected to different learning tasks (spatial discrimination learning in the Morris task and cone-field task, temporal discrimination learning, one-trial inhibitory avoidance task) and noncognitive tests (emotional reactivity, motor coordination, and food motivation) and the relation between the various parameters was assessed. In the learning tasks, except for the inhibitory avoidance task, the first part of the learning curve was taken as an index of learning. Blood glucose (baseline and blood glucose regulation) and hippocampal choline acetyltransferase (ChAT) activity were also measured. There was no correlation between the different parameters of learning in young and old rats. This indicates that there are individual differences in performance in different learning and memory tasks. Measures of noncognitive behavior (food motivation, emotional reactivity, and motor performance) did not predict performance in the learning tasks. Hippocampal ChAT activity did not correlate with learning performance in old rats, whereas blood glucose level was found to correlate with spatial learning in old rats. These results suggest that an impaired regulation of blood glucose may be related to cognitive performance in aging.

Role of collateral behavior in temporal discrimination performance and learning in rats.

Role of collateral behavior in temporal discrimination performance and learning in rats.

Phenylketonuria in the rat associated with decreased temporal discrimination learning.

IN the course of other investigations1 in which tyrosine was injected intraperitoneally it was noted that the level of phenylalanine hydroxylase in the liver of rats was diminished to about one-third the normal value. Since tyrosine added in vitro does not inhibit this enzyme activity2, the results were taken as evidence of product inhibition of enzyme synthesis. It was reasoned that added dietary tyrosine would decrease the enzyme formation and therefore lower the amount of phenylalanine being oxidized to tyrosine; the excess phenylalanine would then be transaminated to phenylpyruvate. Other workers3 had already shown that phenylalanine added to liver slices would also inhibit the oxidation of tyrosine to acetoacetate and fumarate. It seemed worth while therefore to feed various combinations of tyrosine and phenylalanine in order to evaluate metabolic alterations in the rat. Initial experiments with Commercial rat food plus 5 per cent L-tyrosine and 5 per cent DL-phenylalanine resulted in the death of newborn or suckling animals when this diet was fed to the pre-parturient and lactating mothers. The same diet caused death when fed to 21-day-old animals, although animals of the same age grew normally when fed 5 per cent of either amino-acid alone. Reduction of the levels to 2.5 per cent of each amino-acid (and in a later experiment to 3.75 per cent each) caused no difficulty since animals fed this diet gained weight at a rate comparable to that of rats on the commercial diet alone. The methods used for the amino-acid analyses and for enzyme assays have been previously listed1. The urinary and blood data are given in Table 1, and the enzymatic data concerned with phenylalanine and tyrosine metabolism are given in Table 2.