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PubMed2004

Brief communication: the role of category structure in determining the effects of stimulus preexposure on categorization accuracy.

What are the effects of preexposure of stimuli on participants' subsequent ability to categorize them accurately? An experiment employing artificial, abstract, visual stimuli confirms that, for adult humans, the effect of preexposure is dependent upon category structure. Whether preexposure has beneficial or detrimental effects is shown to be dependent on the way category examples are generated from the category base patterns. The results are predicted by salience reduction accounts of perceptual learning but may be problematic for stimulus differentiation accounts.

Adolescent↗
PubMed1986

Ocular dominance and disparity-sensitivity: why there are cells in the visual cortex driven unequally by the two eyes.

Tuning curves for stimulus disparity were constructed for units in area 18 and along the 17/18 border of the cat visual cortex (N = 248). Units were activated with stimuli moving in the same (in-phase motion) or in the opposite direction (antiphase motion) across the two retinae. Over 70% of the units encountered showed sensitivity to stimulus disparity. A clear relationship was found between disparity-sensitivity and unit ocular dominance (OD). Contrary to what might have been expected, large binocular interactions were correlated with unilateral OD. Units highly sensitive to stimulus disparity generally showed strong dominance by one eye (OD groups 1, 2, 6 and 7), or responded well only to binocular stimulation, and weakly or not at all through each eye separately ("binocular-only"). Units unselective for stimulus disparity were usually driven well through either eye (OD groups 3, 4 and 5). High disparity-sensitivity was due to both strong binocular inhibition and strong binocular facilitation in units of extreme unilateral OD. Nearly all units of OD groups 1 and 7 showed clear binocular interactions, indicating that there are few "truly monocular" cells in the cat visual cortex.

Animals↗
PubMed1991

Constructed-response matching to sample and spelling instruction.

The development of interactive programmed instruction using a microcomputer as a teaching machine is described. The program applied a constructed-response matching-to-sample procedure to computer-assisted spelling instruction and review. On each trial, subjects were presented with a sample stimulus and a choice pool consisting of 10 individual letters. In initial training, sample stimuli were arrays of letters, and subjects were taught to construct identical arrays by touching the matching letters in the choice pool. After generalized constructed-response identity matching was established, pictures (line drawings) of common objects were presented as samples. At first, correct spelling was prompted by also presenting the printed name to be "copied" via identity matching; then the prompts were faded out. The program was implemented with 2 mentally retarded individuals. Assessment trials determined appropriate words for training. Correct spelling was established via the prompt-fading procedure; training trials were interspersed among baseline trials that reviewed and maintained spelling of previously learned words. As new words were learned, they were added to a cumulative baseline to generate an individualized review and practice battery for each subject.

Adult↗
PubMed1984

Errorless learning: reinforcement contingencies and stimulus control transfer in delayed prompting.

Delayed prompting can produce errorless discrimination learning. There is inherent in the procedure a disparity in reinforcement density which favors unprompted over prompted responses. We used three schedules of reinforcement to investigate the impact of reinforcement probability on transfer of stimulus control. One schedule of reinforcement was equal prior to and following a prompt (CRF/CRF), the second favored unprompted responses (CRF/FR3), and the third favored responses following the prompt (FR3/CRF). Experimental questions concerned the probability of errors, the probability of transfer, and the rate of transfer in the context of delayed prompting. Transfer was accelerated when reinforcement probability favored anticipatory responding. The schedule that favored prompted responses did not prevent a shift to unprompted responding. Errors were infrequent across procedures. Reinforcement probability contributes to but does not entirely determine transfer of stimulus control from a delayed prompt.

Adolescent↗
PubMed2000

Task demands and representation in long-term repetition priming.

The effects of task demands on the representation of letter strings in long-term repetition priming (LTRP) were explored in two lexical decision experiments. The stimuli in both experiments were words and nonwords, some presented horizontally and some vertically. The only difference between the two experiments was the response required by the participant. In Experiment 1, the participants pressed one of two buttons, indicating whether or not a given stimulus was a word. In Experiment 2, the participants pressed one of four buttons, indicating both the lexical status and the orientation of a given stimulus. The results were that in Experiment 1, LTRP was not disrupted by a change in stimulus orientation, whereas in Experiment 2 it was, suggesting that the nature of the stimulus representation utilized in LTRP is partially dependent on the demands of the task.

Adult↗
PubMed1978

Effects of within-stimulus and extra-stimulus prompting of letter discrimination by mentally retarded persons.

Two different prompting procedures for teaching letter discrimination to mentally retarded persons were compared. Each of 24 severely retarded subjects received training on six alphabet letters, three by extra-stimulus prompting (adding to topographically different cue, a pointing finger) and three by within-stimulus prompting (accentuating critical features of the stimuli themselves). Letter discrimination was tested prior to, immediately following, and 2 weeks after training. A significantly greater proportion of letters trained by within-stimulus prompting was learned (p less than .001), thereby replicating past research with autistic children. Since mentally retarded persons are overselective and attend to few cues in a stimulus array, within-stimulus prompting may be more effective than between-stimulus prompting.

Adult↗
PubMed1992

Stimulus effects of d-amphetamine 1: DA mechanisms.

As part of a continuing effort to assess the role of monoaminergic neuronal systems in the subjective effects of CNS stimulants, 10 rats trained to discriminate 1.0 mg/kg d-amphetamine from saline were treated with compounds that act through different dopaminergic mechanisms. In substitution (generalization) tests, 20 mg/kg of the dopamine (DA) uptake inhibitor GBR 12909 mimicked the training drug completely; at a dose of 15 mg/kg, GBR 12909 substituted for d-amphetamine incompletely. Neither the D1 agonist SK&F 38393 (1, 10 mg/kg) nor the D2 agonist quinpirole (LY 171555; 0.05-0.2 mg/kg) had amphetamine-like effects. When given in combination with the training drug, the D1 antagonist SCH 23390 blocked the amphetamine cue completely at a dose of 0.05 mg/kg but did not have significant effects at higher or lower doses; the D2 antagonist metoclopramide did not block d-amphetamine at any dose tested (1-5 mg/kg). These data indicate that: a) The discriminable effects of d-amphetamine are due, at least in part, to inhibition of DA uptake; b) direct stimulation of either D1 or D2 receptor sites is not sufficient to evoke d-amphetamine-like responding; and c) blockade of D1 receptors attenuates the subjective effects of d-amphetamine to a greater extent than blockade of D2 receptors.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed2000

Myoclonus from selective dentate nucleus degeneration in type 3 Gaucher disease.

OBJECTIVE: To describe a case with a new genetic variant of type 3 Gaucher disease presenting with stimulus-sensitive and action myoclonus in the presence of selective dentate abnormalities. DESIGN: Clinical, pathologic, and molecular genetic studies. SETTING: Medical school departments. PATIENT: A 6-year-old girl with type 3 Gaucher disease experienced progressively crippling generalized stimulus-sensitive and action myoclonus. Repeated electroencephalographic examination did not show cortical activity associated with the myoclonus, suggesting its subcortical origin. Neuropathological examination revealed selective degeneration of the cerebellar dentate nucleus and dentatorubrothalamic pathway in the face of essentially complete lack of storage in the brain. Mutation analysis identified the following 2 mutant alleles: one with a V394L mutation and the other with the lesion RecTL (D409H + L444P + A456P + V460V), which resulted from a recombination event, with the pseudogene located 16 kilobases downstream from the structural gene. CONCLUSION: Given the restricted abnormalities, this genetically unique case provides insight into the pathogenesis of myoclonus and suggests a prominent role for the cerebellar dentate nucleus in its genesis.

Cerebellar Nuclei↗
PubMed1991

Agonist and antagonist properties of serotonergic compounds in pigeons trained to discriminate either quipazine or L-5-hydroxytryptophan.

The serotonin (5-HT) receptor-related compounds metergoline, pirenperone, ketanserin, cyproheptadine, pizotyline, methysergide, lysergic acid diethylamide, mianserin and cinanserin were studied in pigeons trained to discriminate l-5-hydroxytryptophan (l-5-HTP) (18.0 mg/kg) from saline and in pigeons trained to discriminate quipazine (1.0 mg/kg) from saline. Metergoline did not generalize to either quipazine or l-5-HTP but did antagonize drug-appropriate responding in both groups. Ketanserin potently blocked the quipazine discriminative stimulus and neither generalized to nor attenuated the l-5-HTP discriminative stimulus. Pirenperone, cinanserin, cyproheptadine, methylsergide, pizotyline and mianserin attenuated the quipazine discriminative stimulus at low doses and, at higher doses, generalized to the l-5-HTP discriminative stimulus. No antagonism of the l-5-HTP-discriminative stimulus or generalization to the quipazine-discriminative stimulus were observed with these compounds. A correlation coefficient of 0.93 was calculated between the potencies of 5-HT compounds to generalize to the l-5-HTP stimulus and the binding affinities of these compounds for a 5-HT1 receptor in rat brain. In addition, a correlation coefficient of 0.78 was calculated between the potencies of 5-HT compounds to attenuate the quipazine stimulus and the binding affinities of these compounds for the 5-HT2 receptor in rat brain. These observations suggest cyproheptadine, pizotyline, methysergide, lysergic acid diethylamide, mianserin and cinanserin are agonists at the 5-HT1 receptor in the l-5-HTP discrimination and antagonists at a 5-HT2 receptor in the quipazine discrimination in pigeons.

5-Hydroxytryptophan↗
PubMed1992

Irritable esophagus.

An esophageal origin of noncardiac chest pain is generally accepted if prolonged pH and pressure recordings show that the pain episodes correlate in time with acid reflux, esophageal motor abnormalities, or a combination of both, or if provocative testing (acid perfusion, edrophonium, balloon distention) is positive. Many patients with noncardiac chest pain of esophageal origin are said to have an irritable esophagus. Irritable esophagus has been defined in two ways. Some researchers suggest it is actually a lowered esophageal pain threshold, based on the finding that such patients feel chest pain at lower balloon volumes than controls during intraesophageal balloon distention; they are said to be hypersensitive to balloon distention. Hypersensitivity to an esophageal stimulus is generally found in patients with noncardiac chest pain of esophageal origin, and hypersensitivity to a single stimulus is one criterion for a diagnosis. Our group defines irritable esophagus as a condition in which several different stimuli result in the same type of chest pain. Accordingly, we have grouped patients with esophageal chest pain into three categories: (a) patients with an acid-sensitive esophagus, in whom spontaneous pain episodes can be related to acid reflux (with or without accompanying motor disorders), and/or the acid perfusion test is positive; (b) patients with a mechano-sensitive esophagus, in whom the spontaneous pain episodes can be related to motility disturbances (without reflux), and/or the edrophonium test or balloon distention test is positive; (c) patients with an irritable esophagus, in whom some spontaneous pain episodes are related to reflux, while others are related to abnormal motility (without reflux). The last group includes patients whose spontaneous chest pain is related to reflux, with a positive motility tests; whose pain is related to abnormal motility, with a positive reflux test; and patients with positive tests for both reflux and abnormal motility. Seven studies examined a total of 281 noncardiac chest pain patients using prolonged pH and pressure recordings and provocative tests. An acid-sensitive, a mechano-sensitive, or an irritable esophagus was found in 20%, 14%, and 24% of patients, respectively.

Chest Pain↗
PubMed1991

Feedback control of electrically stimulated muscle using simultaneous pulse width and stimulus period modulation.

This paper considers the closed-loop control of electrically stimulated muscle using simultaneous pulse width and frequency modulation. Previous work has experimentally demonstrated good feedback regulation of muscle force using fixed parameter and an adaptive controller modulating pulse width. In this work, it is shown how the addition of pulse frequency modulation to pulse width modulation can improve controller performance. This combination controller has been developed for both single muscle activation and for costimulation of antagonists. This is accomplished using a single command input. In single muscle operation, the combination of pulse width and stimulus pulse frequency modulation results in better control of transient responses than with pulse width modulation alone; the total number of stimulus pulses is increased, however, when compared with pulse width-only modulation at the muscle fusion frequency. In the case of costimulation, the controller modulates the pulse stimulus periods of the antagonists in a reciprocal manner, to ensure stable and fast responses. That is, the frequency of stimulation of the antagonist is increased when that of the agonist is decreased. This results in better control performance with generally fewer stimulus pulses than those generated by costimulation using only pulse width modulation. This feedback controller was evaluated in animal experiments. Step responses with rapid rise times but without overshoot were obtained by the combined modulation. Good steady-state and transient performance were obtained over a wide range of static lengths and commands, under different loading conditions and in different animals. This controller is a promising potential component of neural prostheses to restore functional movement in paralyzed individuals.

Animals↗
PubMed1984

Similarity between (+)-amphetamine and amfonelic acid.

Rats, trained to discriminate the CNS stimulant (+)-amphetamine (1.0 mg/kg) from saline in a two-lever drug administration task, were challenged with various doses of the structurally dissimilar CNS stimulant amfonelic acid. Amfonelic acid was found to substitute for the amphetamine stimulus and was found to be 1.5 times more potent than amphetamine.

Animals↗
PubMed1998

P3a, perceptual distinctiveness, and stimulus modality.

A three-stimulus oddball paradigm (target, standard, nontarget) was employed in which subjects responded to an infrequent target, when its discrimination from the frequent standard was difficult. In separate auditory and visual modality conditions, the stimulus characteristics of an infrequent nontarget were manipulated such that its perceptual distinctiveness from the target was varied systematically. For both the low and high distinctiveness conditions, target stimulus P300 amplitude was larger than the nontarget only at the parietal electrode. In contrast, nontarget P3a amplitude was larger and earlier than the target P300 over the frontal/central electrode sites. The distinctiveness manipulation between the target and nontarget produced larger P3a component profiles for the auditory compared to visual stimuli. The results support previous findings that target/standard stimulus context determines P3a generation for both auditory and visual stimulus modalities and suggest that the distinctiveness of the eliciting stimulus contributes to P3a amplitude. Theoretical implications are discussed.

Acoustic Stimulation↗
PubMed2001

Learning of event sequences is based on response-effect learning: further evidence from a serial reaction task.

Four experiments provide converging evidence that serial learning in a serial reaction task is based on response-effect learning, mediated by the learning of the relations between a response and the stimulus that follows it. In Experiment 1, the authors varied the stimulus sequence and the response-stimulus relations while holding the response sequence constant. Learning effects depended on the complexity of the response-stimulus relations but not on the stimulus-stimulus relations. In Experiment 2, transfer of serial learning from 1 stimulus sequence to another was only found when both sequences had identical response-stimulus relations. In Experiment 3, a variation of the stimulus sequence alone had no effect on serial learning, whereas in Experiment 4 learning effects increased when the response-stimulus relations but not the stimulus-stimulus relations were simplified. These findings suggest that serial learning is based on mechanisms of voluntary action control.

Adult↗
PubMed1991

Associative structure of differential inhibition: implications for models of conditioned inhibition.

Following A+/X- training (with A, X, and + being a light, tone, and footshock, respectively), rats received extinction of A and the training context, extinction of the training context alone, or no extinction. The inhibitory potential of X was then assessed with conditioned lick suppression in a neutral context using both summation and retardation tests. Extinction of the training context alone and extinction of A and the training context reduced the inhibitory potential of X appreciably and equally. Hence, what is traditionally called differential inhibition appears to depend not on the excitatory value of A but on the excitatory value of the training context. In conjunction with what is known about other inhibitory training procedures, these results suggest that a conditioned inhibitor is a stimulus that has been paired with little or no reinforcement in the presence of an accompanying stimulus that predicts greater reinforcement.

Animals↗