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At least 775 records · Page 43Linked to original sources
PubMed2001

Visuo-spatial neural response interactions in early cortical processing during a simple reaction time task: a high-density electrical mapping study.

The timecourse and scalp topography of interactions between neural responses to stimuli in different visual quadrants, straddling either the vertical or horizontal meridian, were studied in 15 subjects. Visual evoked potentials (VEPs) were recorded from 64 electrodes during a simple reaction time (RT) task. VEPs to single stimuli displayed in different quadrants were summed ('sum') and compared to the VEP response from simultaneous stimulation of the same two quadrants ('pair'). These responses would be equivalent if the neural responses to the single stimuli were independent. Divergence between the 'pair' and 'sum' VEPs indicates a neural response interaction. In each visual field, interactions occurred within 72-86 ms post-stimulus over parieto-occipital brain regions. Independent of visual quadrant, RTs were faster for stimulus pairs than single stimuli. This replicates the redundant target effect (RTE) observed for bilateral stimulus pairs and generalizes the RTE to unilateral stimulus pairs. Using Miller's 'race' model inequality (Miller J. Divided attention: evidence for coactivation with redundant signals, Cognitive Psychology 1982;14:247-79), we found that probability summation could fully account for the RTE in each visual field. Although measurements from voltage waveforms replicated the observation of earlier peak P1 latencies for the 'pair' versus 'sum' comparison (Miniussi C, Girelli M, Marzi CA. Neural site of the redundant target effect: electrophysiological evidence. Journal of Cognitive Neuroscience 1998;10:216-30), this did not hold with measurements taken from second derivative (scalp current density) waveforms. Since interaction effects for bilateral stimulus pairs occurred within 86 ms and require interhemispheric transfer, transcallosal volleys must arrive within 86 ms, which is earlier than previously calculated. Interaction effects for bilateral conditions were delayed by approximately 10 ms versus unilateral conditions, consistent with current estimates of interhemispheric transmission time. Interaction effects place an upper limit on the time required for neuronal ensembles to combine inputs from different quadrants of visual space ( approximately 72 ms for unilateral and approximately 82 ms for bilateral conditions).

Adult↗
PubMed1979

Aspects of the reinforcer learned in second-order Pavlovian conditioning.

Four experiments used an autoshaping procedure in pigeons to explore learning about the reinforcer in a second-order conditioning paradigm. Experiment 1 conditioned two visual second-order stimuli (S2), using as reinforcers two visual first-order stimuli (S1), each of which had previously been paired with food. Animals for which the S2 stimuli were each consistently paired with one particular S1 developed second-order responding more rapidly than did animals for which the identity of S1 varied from trial to trial. Moreover, following consistent pairings, extinction of an S1 had a depressive effect upon second-order responding which was peculiar to the S2 with which it had been paired. Both results suggest that in this preparation the organism identifies a particular S1 as the reinforcer for each S2. The remaining experiments examined the details of that identification. A compound S1, itself composed of two separable elements, was used to reinforce an S2. Subsequent extinction of either element of S1 led to a depression in the responding to S2, which indicates that both elements were involved in the second-order conditioning. Moreover, the use of several complex discriminations, which produced different behavior to S1 and to its elements, suggested that the organism had associated the S2 with the compound S1 rather than with its separate elements. However, even complete extinction of the response to S1 left some residual behavior to S2, which indicates that a portion of the second-order conditioning is independent of the current state of the reinforcer. These results demonstrate that in some situations the organism associates a conditioned stimulus with a rich representation of the reinforcer.

Animals↗
PubMed2006

Computer-based measurement of letter and word acuity.

Determining causes of poor reading ability is an important step in trying to ameliorate reading performance in low-vision patients. One important parameter is word acuity. The principal aim of the current study is to develop a method to reliably measure acuities for isolated lowercase letters and words of differing length that can be used to test low-vision patients. Using isolated stimuli means that testing is relatively free of potential crowding and/or distracting attentional effects from surrounding words, it is unambiguous which stimulus subjects are trying to read and response times can be recorded for each stimulus. Across a series of experiments, subjects with normal vision were asked to read isolated lowercase single letters and lowercase words of 4, 7 and 10 letters, in separate tests. Acuities for uppercase Sloan letters were also measured to provide a reference, as they are commonly used to measure visual acuity. Each test was based upon the design principles and scoring procedures used in the Bailey-Lovie and ETDRS charts. Acuities for uppercase Sloan letters were found to be equivalent whether measured using ETDRS charts or the computer-based method. Measurement of acuities for lowercase single letters and lowercase words of 4, 7 and 10 letters had a reliability that was no worse than acuities for uppercase Sloan letters. Lowercase word acuities were essentially independent of word length. Acuities for single lowercase letters and lowercase words were slightly better than uppercase Sloan letters acuity. Optimal processing of lowercase single letters and 4-, 7- and 10-letter words occurred at character sizes that were at least 0.2-0.40 log MAR above acuity threshold, i.e. between 1.5 and 3 times threshold acuity for that particular stimulus. In general, critical character sizes appear similar across word lengths as progressive increases or decreases in these values were not observed as a function of the number of letters in the stimulus. We conclude that a computer-based method of stimulus presentation can be used to obtain highly repeatable measures of acuity for lowercase single letters and lowercase words in normal vision.

Adult↗
PubMed1998

Stimulus context in hemineglect.

Rightward deviation on bisection of a horizontal line is well described in patients with right brain injury and left hemineglect. Because of the observation that hemineglect patients may bisect very short lines to the left of the true midpoint (the so-called crossover effect), additional models have been proposed to incorporate this finding into existing theories of hemineglect. We investigated a line-length effect in six patients with left hemineglect. When presented with any set of lines of uniform (reference) length, percentage rightward deviation on line bisection remained constant across different line lengths. When lines of a second length were mixed into any uniform set of lines, bisection performance on the reference lines changed. A rightward shift in the perceived midpoint of the reference line occurred if the added lines were shorter than the reference lines; a leftward shift occurred if the added lines were longer. Leftward shifts included shifts across the true midpoint, reproducing the crossover effect. Shifts in the perceived midpoint occurred both on a manual line bisection task and on a line bisection discrimination task in which no manual response was required. We propose that the crossover effect may be part of a more general stimulus-context effect in which the perceived midpoint of a line is related not to absolute length, but to the line's length relative to other lines with which it is presented. Such a context effect has not hitherto been described in the neglect syndrome. A possible mechanism for the effect is a generalization of length estimation produced by the combined influence of the focal stimulus and all stimuli that precede it.

Adult↗
PubMed1994

Lesions of central serotonin systems affect responding on a progressive ratio schedule reinforced either by intravenous cocaine or by food.

The effect of intraventricular infusions of the serotonergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), was examined in rats trained on a progressive ratio schedule for either IV cocaine or food reinforcement. Animals in the 5,7-DHT treatment group responded to significantly higher breaking points than vehicle-injected control animals, regardless of whether food or cocaine was used as the reinforcing stimulus. Analysis of the regional brain amines indicated that depletions of mesencephalic 5-HT correlated with postsurgical alterations in responding. These findings suggest that depletion of forebrain 5-HT produces a general effect on responding rather than a specific alteration in the reinforcing effects of psychomotor stimulant drugs.

5,7-Dihydroxytryptamine↗
PubMed2003

Teaching normal development using stimulus videotapes in psychiatric education.

This article examines the educational principles supporting the use of stimulus videotapes. General principles of using videotape in teaching are discussed, followed by a specific review of the literature regarding the uses of videotape in psychiatric education. The literature on the use of stimulus videotape in psychiatric education is reviewed, with particular attention to its use in teaching normal development.

Child↗
PubMed1982

Discrimination of sucrose-taste by the rat as a potential bioassay for sweeteners.

Male hooded rats were trained to discriminate the taste of a sucrose solution from that of water by responding with a lever on one side of a food cup after 20 licks (500 microliter) a 0. M sucrose solution and responding with a lever on the alternating side after 20 licks of water for food reinforcement. All of the rats learned this discrimination reliably. The gustatory stimulus produced by sucrose was concentration dependent (EC50 = 1.3 X 10(-2) M). Saccharin (0.0002-0.002 M), dextrose (0.05-0.25 M), and glycine (0.002-0.2 M) produced a concentration-dependent generalization to the sucrose taste. The EC50 values were 1 X 10(-3), 2.7 X 10(-2), and 1.3 X 10(-1) M, respectively. Solutions of sodium chloride (0.15 M), citric acid (0.01 M), caffeine citrate (0.01 M), quinine hydrochloride (0.001 M), or l-amphetamine sulfate (0.05 M) did not produce sucrose-like taste. Generalization of sweet compounds and lack of generalization of other tastes to the sucrose taste suggest that the procedure of sucrose-water discrimination by the rat has potential in the detection and quantitation of the sweetening properties of new chemicals.

Animals↗
PubMedDate not supplied

Blocking and unconditioned response diminution in human classical autonomic conditioning.

This paper summarizes the results of three experiments on blocking and unconditioned response diminution in human SCR conditioning. Recent theories of conditioning propose that reduced processing of the unconditioned stimulus due to conditioning results in reduced unconditioned response magnitude and in blocking of conditioning of a second conditioned stimulus when it is in compound with the previously conditioned stimulus. In these experiments, clear evidence of diminution of the unconditioned response was obtained in all three studies, but blocking was found only in the third study, which employed a within-subject design and in which the blocking was observed only after at least one extinction trial on both the blocked and nonblocked stimuli. Order of testing was not a factor in this delayed blocking effect. These results do not support the view that blocking occurs because of reduced processing of the unconditioned stimulus in the unconditioned response diminution sense.

Adult↗
PubMed1987

Modulation of the discriminative stimulus produced by pentylenetetrazol by centrally administered drugs.

Pentylenetetrazol is anxiogenic in humans and produces an interoceptive discriminative stimulus in rats which is mimicked by anxiogenic drugs and other treatments and antagonized by anxiolytic drugs. It was proposed that the discriminative stimulus of pentylenetetrazol originates centrally. This hypothesis was tested by injecting small amounts of anxiogenic or anxiolytic drugs into the brain and comparing their ability to mimic or block, respectively, the response to pentylenetetrazol, observed after systemic injection. Food-restricted rats were trained in a two-lever operant task to discriminate the interoceptive discriminative stimulus produced by pentylenetetrazol. Intraperitoneal or intracerebroventricular injection of Ro 5-3663 was substituted in a dose-dependent manner for the stimulus produced by systemically administered pentylenetetrazol. Diazepam injected systemically, blocked the pentylenetetrazol-like stimulus associated with Ro 5-3663 administered systemically or centrally. Midazolam injected intracerebroventricularly and in a dose-dependent manner, antagonized the discriminative stimulus produced by systemic injection of pentylenetetrazol. When injected into the amygdala, midazolam also antagonized in a dose-dependent manner the pentylenetetrazol-induced stimulus. Thus, these data suggest that there are sites in the CNS for both the initiation of a pentylenetetrazol-like stimulus by Ro 5-3663 and the antagonism of the stimulus produced by pentylenetetrazol by midazolam.

Amygdala↗
PubMed1987

Stimulus properties of benzodiazepines: correlations with binding affinities, therapeutic potency, and structure activity relationships (SAR).

Using a two-lever operant choice task, rats were trained to discriminate diazepam (3.0 mg/kg) from saline under a fixed-ratio 10 (FR10) schedule of reinforcement. Once the discrimination was learned, generalization studies were conducted using various doses of 17 benzodiazepine derivatives. The diazepam stimulus generalized in a dose-related manner to each of these compounds. ED50 values were compared with available data on displacing affinities (Ki values) for tritiated diazepam brain binding in man, and with human therapeutic potency. A significant correlation (r = 0.88, n = 9) was found between benzodiazepine binding affinities and ED50 values derived from the diazepam stimulus generalization assay. A significant correlation (r = 0.92, n = 10) was also found between drug discrimination ED50 values and human therapeutic potencies. Finally, the benzodiazepine structure activity relationships generated from the drug discrimination studies closely paralleled the known structure activity relationships for these agents. The results provide further evidence that benzodiazepines exert their pharmacological effects through an interaction with benzodiazepine receptors.

Animals↗
PubMed1999

Inability of antipsychotics to antagonize the cueing properties of cocaine in rats.

In this study the possible antagonistic effects of five different antipsychotics on the discriminative stimulus properties of 10 mg/kg cocaine were evaluated by use of a two-lever food-reinforced drug discrimination procedure in rats. To do so, rats were treated with several doses of haloperidol, risperidone, seroquel, sertindole, and olanzapine, either at 60 or 120 min prior to testing. With all compounds tested, no substantial antagonism of the cocaine cue was observed. Only with haloperidol (maximum 60%), risperidone (maximal 20%), and olanzapine (maximal 20%) a partial antagonism without clearcut dose-response was observed. Clozapine, seroquel, and sertindole did not influence the discriminative stimulus properties of cocaine. These results indicate that antipsychotics with different pharmacological profiles are unable to antagonize more than partially the cueing properties of 10 mg/kg cocaine in rats, pointing to the unique underlying stimulus properties of this stimulant.

Animals↗