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PubMed2005

Training of somatosensory discrimination after stroke: facilitation of stimulus generalization.

OBJECTIVE: Task-specific learning typifies perceptual training but limits rehabilitation of sensory deficit after stroke. We therefore investigated spontaneous and procedurally facilitated transfer of training effects within the somatosensory domain after stroke. DESIGN: Ten single-case, multiple-baseline experiments were conducted with stroke participants who had impaired discrimination of touch or limb-position sense. Each experiment comprised three phases: baseline, stimulus-specific training of the primary discrimination stimulus, and either stimulus-specific training of the transfer stimulus or stimulus-generalization training. Both the trained and transfer stimuli were monitored throughout using quantitative, norm-referenced measures. Data were analyzed using individual time-series analysis and meta-analysis of intervention effects across case experiments. RESULTS: Stimulus-specific training was successful for trained texture and proprioceptive discriminations, but it failed to show spontaneous transfer to related untrained stimuli in the same modality in seven of eight experiments in which this was possible. In contrast, intramodality transfer was obtained with stimulus-generalization training in four of five experiments that investigated stimulus-generalization training of texture discrimination. Findings were confirmed by meta-analysis. CONCLUSIONS: Our findings demonstrate generalization of training within a somatosensory modality poststroke, provided that a program designed to enhance transfer is used. This has implications for the design of efficient rehabilitation programs.

Adult↗
PubMed1976

Stimulus generalization: some predictions from a model of Pavlovian conditioning.

Three experiments examined predictions generated by incorporating a common-elements account of stimulus generalization within the Rescorla-Wagner model of conditioning. All experiments employed rats in a conditioned suppression situation. Experiments 1 and 2 found that conditioning of a similar stimulus augmented the excitation controlled by a near-asymptotic target stimulus more than did further conditioning of the target itself. Prior discrimination training between the target and the similar stimulus enlarged this effect, compared with prior discrimination between the target and another dissimilar stimulus. Nonreinforced exposure of the similar stimulus prior to its reinforcement also increased the effect. Experiment 3 examined a related prediction for inhibition. After discrimination training, extinction of the previously reinforced stimulus revealed more inhibition to the previously nonreinforced stimulus when those two stimuli were more similar. These outcomes are consistent with deductions from the present model and encourage further testing of its expansion to the case of stimulus generalization.

Acoustic Stimulation↗
PubMed1975

Stimulus generalization and anxiety in schizophrenic and normal subjects.

Sixty schizophrenics and 60 normal subjects were compared on a test of stimulus generalization. The generalization stimuli were lines differing in length. Both schizophrenics and normals were divided into two groups (30 subjects each) and trained either on a short line or on a long line. In addition to the generalization stimuli, subjects were presented with an irrelevant stimulus (circle). Although there was a significant difference between the generalization gradients of the groups, this difference was limited to generalization stimuli away from the negative training stimulus. The concept of peak shift was invoked to interpret these data. That the groups did not respond to the irrelevant stimulus is inconsistent with interference theory and gives some support to the differentiation between conceptual overinclusion and perceptual overinclusion. The relationship between stimulus generalization and scores on the Manifest Anxiety Scale was inconsistent.

Anxiety↗
PubMed2003

CS-specific gamma, theta, and alpha EEG activity detected in stimulus generalization following induction of behavioral memory by stimulation of the nucleus basalis.

Tone paired with stimulation of the nucleus basalis (NB) induces behavioral memory that is specific to the frequency of the conditioned stimulus (CS), assessed by cardiac and respiration behavior during post-training stimulus generalization testing. This paper focuses on CS-specific spectral and temporal features of conditioned EEG activation. Adult male Sprague-Dawley rats, chronically implanted with a stimulating electrode in the NB and a recording electrode in the ipsilateral auditory cortex, received either tone (6kHz, 70dB, 2s) paired with co-terminating stimulation of the nucleus basalis (0.2s, 100Hz, 80-105 microA, ITI approximately 45s) or unpaired presentation of the stimuli (approximately 200 trials/day for approximately 14 days). CS-specificity was tested 24h post-training by presenting test tones to obtain generalization gradients for the EEG, heart rate, and respiration. Behavioral memory was evident in cardiac and respiratory responses that were maximal to the CS frequency of 6kHz. FFT analyses of tone-elicited changes of power in the delta, theta, alpha, beta1, beta2, and gamma bands in the paired group revealed that conditioned EEG activation (shift from lower to higher frequencies) was differentially spectrally and temporally specific: theta, and alpha to a lesser extent, decreased selectively to 6kHz during and for several seconds following tone presentation while gamma power increased transiently during and after 6kHz. Delta exhibited no CS-specificity and the beta bands showed transient specificity only after several seconds. The unpaired group exhibited neither CS-specific behavioral nor EEG effects. Thus, stimulus generalization tests reveal that conditioned EEG activation is not unitary but rather reflects CS-specificity, with band-selective markers for specific, associative neural processes in learning and memory.

Acoustic Stimulation↗
PubMed1966

A comparison of different measures of response strength in the study of stimulus generalization.

In Experiment 1, three pigeons were given variable interval training to peck at a light of 550 mmu and then were tested for stimulus generalization in extinction to several different wavelengths. A gradient was obtained for latency of the first response in each test period, for the number of test periods in which responding occurred, and for the measure of response rate. When the response rate gradient was corrected for differences in initial latency and in number of responded trials, the change was minimal, indicating that the major component of response rate as usually measured is rate of responding having once responded. In Experiment 2, three other pigeons were trained to respond to 550 mmu (for variable interval reinforcement) and not to 570 mmu (extinguished). Analysis of generalization gradients dictated the same conclusion as that reported for generalization following single stimulus training.

Animals↗
PubMed1977

Stimulus generalization from feeder to response key in the acquisition of autoshaped pecking.

During autoshaping, a 6-second presentation of one stimulus and a variable time 30-second presentation of a second stimulus alternated in appearance on a pigeon key. Grain always was delivered for 3 seconds at the end of the first stimulus interval. In the first experiment, autoshaped pecking of the stimulus preceding grain delivery began much sooner when that stimulus was a black vertical line on a white background and the other stimulus was green than when the opposite stimulus arrangement was used. Because these two stimuli differed in form, hue, brightness, and similarity in hue and brightness to the illumination of the raised feeder, three subsequent experiments examined whether the differential speed of autoshaping in the two groups was due to a feature-positive, feature-negative effect, a preference for brighter over darker stimuli, a simple preference for white over green, or stimulus generalization from the brightness or hue of the illuminated, raised feeder to the stimulus on the key preceding grain delivery. The data from these experiments showed that the first autoshaped key peck was most likely to be made to the stimulus of the same hue as that illuminating the feeder, regardless of whether that stimulus was positively or negatively associated with grain delivery. At least under some conditions, therefore, stimulus-generalization mediated response transfer of pecking grain in the presence of the hue illuminating the feeder to pecking the key illuminated by a similar hue appears to account for the occurrence of autoshaped key pecking.

Journal Article↗
PubMed1968

The peak shift in stimulus generalization: equivalent effects of errors and noncontingent shock.

Terrace suggested that the peak shift in stimulus generalization occurs because the training stimulus not correlated with reinforcement has become aversive. This hypothesis is plausible in the light of instances where the peak shift is obtained compared with those where it fails to appear. The present experiment attempted to test implications of this hypothesis. Two groups of pigeons learned the same two-stimulus discrimination between colors by different training methods in a free-operant situation. When the discrimination was trained with many errors, a large peak shift was obtained in a subsequent generalization test of wavelength; after discrimination training with few errors, a negligible shift was observed. Half of each group then received noncontingent aversive shock during presentations of the stimulus not correlated with reinforcement in continued discrimination training. After this treatment, the errorless-shock subgroup showed a large peak shift and the error-shock subgroup tended to show a larger shift than before. Nonshocked control groups showed little change in the peak shift. It was concluded that pairing aversive shock with a stimulus not correlated with reinforcement is sufficient to produce or enhance a peak shift. In their effect on the peak shift, aversive shock and large amounts of nonreinforced responding appear to be equivalent.

Analysis of Variance↗
PubMed1975

Latent inhibition and stimulus generalization of the classically conditioned nictitating membrane response in rabbits (Oryctolagus cuniculus) following dorsal hippocampal ablation.

Rabbits received 0 to 450 exposures of a tone conditioned stimulus (CS) prior to classical defensive conditioning of the nicitating membrane response based on an infraorbital eye shock unconditioned stimulus. Tone preexposure resulted in retarded conditioning in normal rabbits. This latent inhibition effect was not present in animals with bilateral dorsal hippocampectomy produced by aspiration. Control animals with bilateral neocortical and callosal aspiration lesions demonstrated a latent inhibition effect similar to that shown by normal nonoperated animals. The failure of CS preexposure to retard conditioning in hippocampal rabbits was not due to differences in threshold of the conditioned response to the CS or to differences in response mechanisms as determined by tests of habituation and dishabituation of the unconditioned response. A subsequent experiment employed combined-cue summation tests to confirm the fact that preexposure did not endow the tone with conditioned as well as latent inhibitiory properties. Finally, tests of stimulus generalization along the auditory frequency dimension indicated flatter relative gradients for hippocampals than for nonoperated controls, with cortical controls in between. These findings were discussed in terms of Douglas' model of hippocampal function.

Acoustic Stimulation↗
PubMed1993

Cocaine-stimulus generalization to two new designer drugs: methcathinone and 4-methylaminorex.

Rats were trained to discriminate 8 mg/kg cocaine from saline vehicle for the purpose of examining the stimulus properties of two novel and structurally related drugs of abuse recently confiscated on the illicit market: (+/-)methcathinone and cis(+/-)4-methylaminorex. The stimulus properties of these controlled substance analogs were compared with those of their parent compounds (+/-)cathinone and aminorex, respectively. All agents resulted in cocaine-stimulus generalization with the following rank order of potency: aminorex (ED50 value = 0.8 microM/kg) > methcathinone (1.9 microM/kg) > cathinone (3.7 microM/kg) > 4-methylaminorex (5.2 microM/kg) > cocaine (7.6 microM/kg).

Animals↗
PubMed1991

Measures of stimulus generalization in drug discrimination experiments.

Different approaches to measuring stimulus generalization in drug discrimination experiments are compared. The main issue, with implications for interpreting partial generalization, has been whether it is preferable to use graded or quantal indices. The first step is to determine whether discriminative drug effects are inherently quantal or graded; it would be pointless to attempt to assess a quantal phenomenon with a graded index. Evidence is reviewed suggesting that behavioural variables, and possibly pharmacological variables as well, determine the nature of the effects. Certain experiments used to evaluate the nature of generalization with exteroceptive stimuli have yet to be applied to the interoceptive stimuli that drugs produce. However, like many other attributes of drug action, discriminative stimulus effects are not immutable in nature, but are malleable and influenced by variables such as the schedule of reinforcement. There appears to be a potential for selecting procedures that generate graded responding in order to maximise precision. This ideal situation has yet to be fully realised in practice since the optimal conditions for generating graded responding remain to be identified, and present indices, based on percentage scores, do not generate interval scales of measurement. Until these issues are resolved, there is no case for maintaining that measurements of discriminative drug effects should with advantage be always quantal or always graded; either approach is compatible with research of high quality and can generate valid results and conclusions.

Journal Article↗
PubMed1975

"Stimulus generalization" between differentiated visual, auditory, and central stimuli.

Cats were trained to discriminate between two different repetition rates of flicker and of click. Both approach-approach and avoidance-avoidance discriminations were used. After substantial overtraining, transfer of frequency discrimination was initiated to stimulation of the reticular formation using bursts of electrical pulses at the same two repetition rates. Significant levels of discriminated performance were obtained in all cats very quickly, indicating good cross-modal transfer between the peripheral discriminanda and the central stimuli. The literature on stimulus generalization and cross-modal transfer is reviewed and the findings of this experiment are discussed in that context. Certain conditions are defined which, if satisfied, justify the interpretation that stimulus generalization or rapid cross-modal transfer indicate that facilitation of subsequent tasks in a training sequence can be attributed to mediation by a specific neuronal mechanism established by training on a previous task. The present experiment was designed in view of such criteria. The evidence of good cross-modal transfer is interpreted to mean that brain mechanisms storing memories about discriminations between visual or auditory stimuli with different repetition rates can be effectively activated by gross electrical stimuli at the same repetition rates. Conflict trials were then carried out in which flicker or click at either frequency was contradicted by concurrent RF stimuli at the other frequency. As the current level of RF stimuli was parametrically increased, it was found that the central stimuli achieved almost complete control over the behavioral outcome in most cases. Concurrent transfer of training, using a counterbalanced training sequence, was then carried out to stimulation of the visual cortex, lateral geniculate, medial geniculate, and the intralaminar nuclei of the thalamus. In each case, rapid transfer was displayed by at least one animal. Once performance to brain stimulation at a given repition rate was established, little change was observed when the fine structure of the stimulus was altered by changing parameters of the stimulus burst. These findings are interpreted as providing support for a statistical theory of memory, since they constitute evidence that previously learned discriminative behavior can readily be elicited by compelling large ensembles of neurons in various brain regions to discharge with particular temporal patterns. It is difficult to reconcile these results with theories which postulate that learning establishes new synaptic pathways in which discharge must occur for memories to be retrieved.

Animals↗
PubMed1984

Stimulus generalization of conditioned taste aversion in rats.

Relatively little information is available regarding the intradimensional stimulus generalization of conditioned taste aversion (CTA). Experiment 1 employed a between-groups generalization test to examine the extent to which conditioned flavor aversion to one sucrose solution generalized to other concentrations of sucrose in adult rats. Evidence of a gradient of aversion was obtained. Because generalization gradients in other tasks have been found to flatten over a retention interval, Experiment 2 investigated the effects of delayed testing (2, 7, or 21 days) upon the slope of the generalization gradient. The generalization gradient flattened at the intervals, suggesting that subjects forgot the specific attributes of the conditioning concentration and avoided generalized stimuli as if they were the original CS. Experiment 3 used a long delay between taste and toxicosis to degrade the associative contingency and found no evidence that the generalization gradients found in the first two experiments could be explained in terms of enhanced neophobia due to poisoning. These findings provide further evidence (cf. A. W. Logue, 1979, Psychological Bulletin, 86, 276-296; M. Domjan, 1980, in J. S. Rosenblatt, R. A. Hinde, C. Beer, & M. Busnel (Eds.), Advances in the study of behavior, Vol. 11, New York: Academic Press) that CTA shares a number of similarities with other learning processes. Further, they illustrate that stimulus forgetting can be detected in a paradigm considered relatively immune to retention loss.

Animals↗
PubMed1977

Subcutaneous injections of apomorphine, stimulus generalization and conditioning: serious pitfalls for the examiner using apomorphine as a tool.

This report shows that stimulus generalization occurs in rats conditioned by a single injection of apomorphine. The data suggest that apomorphine initially acts as an unconditioned stimulus (UCS) of an unconditioned response (UCR) that, in turn, produces stimuli which become conditioned stimuli (CS) of a conditioned response (CR) having a nature identical to that of the UCR. The study also shows that behaviour elicited by a subcutaneous injection of apomorphine depends on the part of the body selected for administration. The mentioned properties should be taken into account when apomorphine is used as a tool in studies on brain and behaviour.

Animals↗
PubMed1999

Lack of difference between HAD and LAD rats in the stimulus generalization of ethanol to nicotine.

High alcohol drinking (HAD) and low alcohol drinking (LAD) rats were trained to discriminate 0.5 g/kg ethanol from saline. HAD and LAD rats learned the discrimination at the same rate and to the same level of asymptotic performance. In substitution tests, increasing doses of ethanol produced increased responding on the ethanol lever with dose-effect curves that were very similar in HAD and LAD rats. There was no generalization from ethanol to nicotine, or d-amphetamine, in either HAD or LAD rats. These data may be contrasted with data obtained with alcohol preferring rats (P rats) and alcohol non-preferring rats (NP rats), where the ethanol discrimination was learned more rapidly, asymptotic performance was better in P than in NP rats, and ethanol discriminative stimulus generalized to nicotine and partially to d-amphetamine in P, but not in NP rats. These data suggest that the differences in ethanol consumption reported previously by P and HAD rats relative to NP and LAD rats is not necessarily related to strain differences in ethanol discrimination as the differences in ethanol discrimination previously observed between P and NP rats do not occur in HAD and LAD rats.

Alcohol Drinking↗
PubMed2005

Distinct patterns of stimulus generalization of increases and decreases in VOR gain.

Motor learning must be capable of increasing or decreasing the amplitude of movements to meet the demands of the environment. One way to implement such opposite learned changes would be to store them with bidirectional plasticity mechanisms (i.e., long-term potentiation and depression at the same synapses). At the behavioral level, this scheme should result in similar patterns of stimulus generalization of increases and decreases in movement amplitude because the same synapses would be modified but in opposite directions. To test this idea, we quantitatively compared the stimulus generalization of learned increases and decreases in the gain (amplitude) of the vestibuloocular reflex (VOR) in mice and in monkeys. When examined across different sinusoidal frequencies of head rotation, decreases in VOR gain generalized more than increases in gain. This difference was apparent not only in the gain, but also the phase (timing) of the VOR. Furthermore, this difference held when animals were trained with high-frequency rotational stimuli, a manipulation that enhances frequency generalization. Our results suggest that increases and decreases in VOR gain are not exact inverses at the circuit level. At one or more sites, the plasticity mechanisms supporting decreases in VOR gain must be less synapse-specific, or affect neurons more broadly tuned for head rotation frequency, than the mechanisms supporting increases in gain.

Adaptation, Physiological↗
PubMed1964

STIMULUS GENERALIZATION AND THE RESPONSE-REINFORCEMENT CONTINGENCY.

Generalization gradients along a line-tilt continuum were obtained from groups of pigeons that had been trained to peck a key on different schedules of reinforcement. In Exp. I, gradients following training on a differential-reinforcement-of-low-rate (DRL) schedule proved to be much flatter than gradients following the usual 1-min variable interval (VI) training. In Exp. II, the value of the VI schedule itself was parametrically studied; Ss trained on long VI schedules (e.g., 4-min) produced much flatter gradients than Ss trained on short VI schedules (30-sec; 1-min). The results were interpreted mainly in terms of the relative control exerted by internal, proprioceptive cues on the different reinforcement schedules. Several implications of the results for other problems in the field of stimulus generalization are discussed.

Animals↗