Simple Visual Discrimination Task Research Articles

Learning impairments induced by glutamate blockade using dizocilpine (MK-801) in monkeys.

1. This study investigated the effects of dizocilpine (MK-801) on learning ability in a non-human primate. Acquisition and reversal learning of visual discrimination tasks and acquisition of visuo-spatial discrimination tasks were assessed in marmosets using the Wisconsin General Test Apparatus. Dizocilpine impaired acquisition of visuo-spatial (conditional) tasks requiring spatial responses to coloured objects, and perceptually difficult visual discrimination tasks in which stimulus objects are painted black. Dizocilpine did not, however, impair either acquisition or reversal of a simple visual discrimination task using easily discriminated, coloured objects. 2. Motor effects of dizocilpine treatment, which have been seen in other primates, were examined by observation of the marmosets in their home cages, using both an automated locomotor activity monitor and 'blind', subjective counting of the number of abnormal movements in a given time period. Locomotor activity, assessed using the automated monitor, was not significantly affected at any of the doses tested. Incoordination, assessed by human observation of abnormal movements, was significantly increased only at a dose of 30 microg kg(-1) i.m., which was twice the highest dose used to assess the effects of dizocilpine on cognition. 3. We have, therefore, found an effect of dizocilpine on acquisition and reversal of some types of cognitive task, at a dose which does not cause significant motor effects. This demonstration of a cognitive deficit associated with glutamatergic blockade in a primate may be useful in understanding the contribution of glutamatergic dysfunction to cognitive decline in neurodegenerative disease, especially Alzheimer's disease.

Sources of individual differences in IT

Interest in inspection time (IT), uniformly thought to index ‘speed-of-processing’, has been maintained because of its established empirical correlation with general mental ability and performance IQ measures. The IT procedure generally consists of a simple visual discrimination task displayed at various critical exposure durations and immediately followed by a suitable mask. Processing is assumed to terminate at mask onset, which seems inappropriate in light of the target/mask composite necessarily available with integration theories of backward masking. The present paper reports five experiments involving attended and unattended secondary stimuli and additional factor analyses of previous studies involving IT. From these it is proposed that IT is better thought of as indexing the power an individual can bring to bear within a specific cognitive domain rather than ‘speed-of-processing’ per se. The consequence is that the observed IT-IQ correlation is merely the inevitable outcome of measuring the same domain with two different tasks; rather than due to some elemental factor such as mental speed underlying both tasks. Ways in which this model could be tested are discussed.

Hippocampal and neocortical cell assemblies encode memory processes for different types of stimuli in the rat

The objective of this study was to determine whether each of several different memory processes is encoded exclusively by specific single neurons (single-neuron coding) or by overlapped groups of neurons (population coding by cell assembly). Single neuronal activity was recorded from the rat hippocampal formation (CA1, CA3, dentate gyrus) and temporal cortex during the performance of simple auditory, simple visual, and configural auditory-visual discrimination tasks. All the tasks employed the identical apparatus and time parameters and differed only in the type of stimuli to be processed for correct performance. Single neurons showing significantly differential activity among the discriminative stimuli in each task were judged to be task-related and involved in the memory process of the task. Of the total number of neurons recorded from the hippocampal formation and temporal cortex, 21-26% of the neurons showed task-related activity in only one task, in two tasks, or in all three tasks. This result indicates some overlapping among the neurons involved in each of teh different memory processes. A cross-correlation analysis tested activity correlations among the neurons recorded simultaneously. Most pairs of the hippocampal neurons related to the same tasks (same memory processes) showed correlations during performance of the related tasks. This result showing coactivation of the same types of task-related neurons, together with the result showing the overlapping of task-related neurons, supports the concept of population coding by cell assemblies specifically in the hippocampal formation during memory processing.

P300 differences between sinistrals and dextrals

The P3(00) event-related potential (ERP) was elicited in 20 left- and 20 normal right-handed young adult male subjects using a simple visual stimulus discrimination task. For left-compared to right-handed subjects, P3 amplitude was larger at anterior electrode sites for the target stimuli and larger overall for the novel visual stimuli; P3 latency was shorter for left-compared to right-handers for the target stimuli. The N1, P2, and N2 components demonstrated similar handedness effects. The relationships of ERP amplitude and handedness to anatomical variables and cognitive factors are discussed.

P300 hemispheric amplitude asymmetries from a visual oddball task

The P3(00) event-related potential (ERP) was elicited in 80 normal, right-handed male subjects using a simple visual discrimination task, with electroencephalographic (EEG) activity recorded at 19 electrodes. P3 amplitude was larger over the right than over the left hemisphere electrode sites primarily at anteromedial locations (F3/4, C3/4) for target, novel, and standard stimuli. The N1, P2, and N2 components also demonstrated hemispheric asymmetries. The strongest P3 hemispheric asymmetries for all stimuli were observed at anterior locations, suggesting a frontal right hemisphere localization for initial stimulus processing, although target stimuli produced larger P3 amplitudes at parietal locations that did novel stimuli. The relationships of hemispheric asymmetries to anatomical variables, background EEG activity, and neurocognitive factors are discussed.

Conditional learning and memory impairments following neurotoxic lesion of the CA1 field of the hippocampus

Monkeys with bilateral lesions of the CA1 field of the hippocampus produced by the injection of neurotoxin diagonally along the length of the hippocampus were found to have a severe impairment on the retention of a conditional task learnt prior to surgery and on the new acquisition of several types of this task. They were equally impaired on conditional tasks that required a spatial response or an object choice in response to either visual or spatial cues. They were not impaired on simple visual discrimination tasks, simple spatial discrimination tasks or reversal learning of these tasks. This patterns of impairment resembles that seen in the same species with neurotoxic lesions within the vertical limb of the diagonal band of Broca or transection of the fornix. Monkeys with subtotal lesions of the adjacent medial temporal area were not consistently impaired on any of these tasks. The results suggest that hippocampal lesions produce anterograde and retrograde amnesia for information other than reward association.

Effects of aging upon recent memory in Microcebus murinus

Four young (2 to 4-year-old) and four aged (9 to 10-year-old) grey mouse lemurs (Microcebus murinus) were given a simple visual discrimination task, and a delayed response visual discrimination task with variable retention delay. The response to the test is a motor one, that consists of choosing one out of four corridors of an apparatus based upon the degree of illumination. The aged animals did not show any learning deficiency, and were capable of memorizing the task for several months. However, they were more sensitive to the length of the delay in the delayed response task than the young animals. It is, therefore, possible to argue that the memory for recent stimulus events is affected during aging. These results corroborate those obtained in other primates, and demonstrate the usefulness of the grey mouse lemur as a new animal model for analyzing aging.

Spatio-temporal stages in face and word processing. 1. Depth recorded potentials in the human occipital and parietal lobes

Evoked potentials (EPs) were used to help identify the timing, location, and intensity of the information-processing stages applied to faces and words in humans. EP generators were localized using intracranial recordings in 33 patients with depth electrodes implanted in order to direct surgical treatment of drug-resistant epilepsy. While awaiting spontaneous seizure onset, the patients gave their fully informed consent to perform cognitive tasks. Depth recordings were obtained from 1198 sites in the occipital, temporal and parietal cortices, and in the limbic system (amygdala, hippocampal formation and posterior cingulate gyrus). Twenty-three patients received a declarative memory recognition task in which faces of previously unfamiliar young adults without verbalizable distinguishing features were exposed for 300 ms every 3 s; 25 patients received an analogous task using words. For component identification, some patients also received simple auditory (21 patients) or visual (12 patients) discrimination tasks. Eight successive EP stages preceding the behavioral response (at about 600 ms) could be distinguished by latency, and each of 14 anatomical structures was found to participate in 2-8 of these stages. The earliest response, an N75-P105, focal in the most medial and posterior of the leads implanted in the occipital lobe (lingual g), was probably generated in visual cortical areas 17 and 18. These components were not visible in response to words, presumably because words were presented foveally. A focal evoked alpha rhythm to both words and faces was also noted in the lingual g. This was followed by an N130-P180-N240 focal and polarity-inverting in the basal occipitotemporal cortex (fusiform g, probably areas 19 and 37). In most cases, the P180 was evoked only by faces, and not by words, letters or symbols. Although largest in the fusiform g this sequence of potentials (especially the N240) was also observed in the supramarginal g, posterior superior and middle temporal g, posterior cingulate g, and posterior hippocampal formation. The N130, but not later components of this complex, was observed in the anterior hippocampus and amygdala. Faces only also evoked longer-latency potentials up to 600 ms in the right fusiform g. Words only evoked a series of potentials beginning at 190 ms and extending to 600 ms in the fusiform g and near the angular g (especially left). Both words and faces evoked a N150-P200-PN260 in the lingual g, and posterior inferior and middle temporal g.(ABSTRACT TRUNCATED AT 400 WORDS)

PET-FDG test-retest reliability during a visual discrimination task in schizophrenia.

Reliability of assessment is important in any kind of neuropsychiatric study, but is particularly pivotal in schizophrenia research where symptom instability is common. Two fluorodeoxyglucose PET scans, 1 week apart, were carried out in schizophrenic patients while they were performing a simple visual discrimination task. Subject and scan conditions were held constant. Regional metabolic rates of glucose utilization were calculated as absolute and scaled; they were compared using correlational statistics. Average differences between scans were 5-9% for the parietal and occipital cortices, but 1-3% for other cortical areas, differences comparable with reported variances in normal controls. These results suggest that test-retest variance in metabolic imaging in schizophrenia is relatively low and that task performance increases metabolic stability in brain areas unrelated to task performance.

Monitoring Automation Failures: Effects of Automation Reliability and Task Complexity

Two studies examined the effects of automation reliability and task complexity on the monitoring of automation failures during performance of a flight-simulation task. In the first study, 24 students performed tracking and resource management tasks while an automation routine monitored for system malfunctions over four 30-minute sessions Detection of automation failures was significantly higher for variable reliability automation (mean = 81.6%) than for constant reliability automation (mean = 32.7%), indicating that constant-reliability automation induced complacency in monitoring. The effect of automation reliability was eliminated when 16 more subjects were required to complete the monitoring task only. Neither group of subjects exhibited a vigilance decrement. In the second study monitoring performance and vigilance decrement were examined for a situation in which only one automation failure occurred during a session. 36 students were randomly assigned to one of three task groups: simple (visual discrimination task), single-complex (monitoring only) or multi-complex (tracking, resource management, and monitoring). In both the simple and the multi-complex tasks, more subjects detected the automation failure in the first ten minutes of a session than in the last ten minutes of a session (67%-17% and 75%-42% respectively). Subjects in the single-complex condition detected the automation failure equally well in both time periods (92%-83%). The results point to two areas of potential costs in the automation of a task: (1) constant patterns of automation reliability can lead to inefficiency in monitoring automation failures; and (2) infrequent automation failures in multi-task conditions can lead to a vigilance decrement. While these costs should not prohibit the implementation of automation, they should be considered in the design of any automated system.

Acute effects of oral low doses of pyridostigmine on simple visual discrimination and unconditioned consummatory acts in rats

Pyridostigmine bromide (Pyr), a reversible cholinesterase inhibitor, is currently suggested to be the most effective pretreatment drug against intoxication with potent organophosphates (OP). This investigation was conducted to determine if oral low doses of Pyr would affect performance of a simple visual discrimination task, and further to assess the alterations of motor or motivational function that might underlie the performance deficits in the water-deprived rats. Rats were trained extensively on a successive light-intensity discrimination implemented with the use of a multiple schedule. The multiple schedule consisted of one fixed-ratio (FR-10) and one differential reinforcement of low rates (DRL-10 s) component, which were signalled by the 10-s discriminative stimuli of bright (S +) and dim (S −) houselights, respectively, in simple alternation. The light intensity difference (S −/S +) was about 0.6 Pyr, at doses (3–12 mg/kg), which did not cause overt symptoms, moderately decreased S + respondings but did not affect S − respondings. The ratio of S +/S − respondings, an index of discrimination performance, was moderately decreased. Over the range of doses evaluated, Pyr also attenuated the corresponding water intake in a dose-dependent manner, but it did not significantly affect locomotor activity. The lowest effective doses of the above affected behaviors were virtually identical (6 mg/kg). These results suggest that the disruptive effects of a single oral low dose of Pyr on the rat operant performance involve motivational dysfunction rather than motor impairment.

Potentiation of neuronal responses to natural visual input paired with postsynaptic activation in the hippocampus of the awake monkey

Extracellular recordings were made in the hippocampal formation while the monkey performed a simple visual discrimination task in which the stimuli consisted of coloured patterns presented serially. By using this natural visual input to single hippocampal neurones, and experimentally pairing one of the stimuli with postsynaptic excitation induced by iontophoretically applied l-glutamate, we demonstrate that selective synaptic potentiation can result. Seven of 29 neurones tested showed potentiation. The potentiation was selective in that enhanced responses only occurred to the previously paired stimulus, and not to other visual stimuli. The potentiation was observed in CA3 neurones and lasted approximately 15 min. In each case the latency of the potentiated response occurred at 160 ms following the onset time of the stimulus.

Visual memory lateralization in pigeons

Previous experiments employing simple visual discrimination tasks have revealed a cerebral lateralization in the visual system of pigeons with a dominance of the left hemisphere. Until now, visual memory lateralization in birds has not been investigated. To study possible asymmetries of visual memory functions, a simultaneous instrumental discrimination procedure was used. The animals were trained to discriminate 100 different visual patterns from a further 625 similar stimuli. Retention tests were conducted under binocular and monocular conditions. When the subjects looked monocularly, retention performance was significantly higher with the right eye (left hemisphere) than with the left eye (right hemisphere). The results suggest that the lateralization of the pigeon's visual system depends at least partly on an asymmetry in visual memory capacity.

S+ versus S- fading in teaching visual discriminations to severely mentally handicapped children.

Twenty-seven severely mentally handicapped children in three matched groups were trained on both a complex and a simple visual discrimination task with: (1) prompt fading on S+; (2) prompt fading on S-; or (3) no prompting (trial-and-error training). On the complex discrimination task, differences between groups were obscured by a floor effect. Only one subject from each group acquired the discrimination. However, on the simple discrimination task all nine S+ fading, eight S- fading and six trial-and-error training subjects attained criterion. Both S+ and S- fading groups made significantly fewer errors than the trial-and-error group but did not differ significantly from each other. Sixteen children who failed to acquire the complex discrimination in Experiment 1 also participated in Experiment 2. Subjects received additional training on the task by one of four procedures. Neither continued trial-and-error training, continued S+ or S- fading, reversals of the prompt between S+ and S-, or intensity fading resulted in acquisition of the task. Results are discussed in terms of overshadowing and task difficulty.

Measurement of the alpha-cell-migration in the entorhinal region: A marker for the developmental disturbances in schizophrenia? : P. Falkai∗, B. Bogerts∗, G.W. Roberts∗∗ and T.J. Crow∗∗ ∗Department of Psychiatry, University of Düsseldorf, Bergische Landstrasse 2, 4000 Düsseldorf 12, FRG; and ∗∗Division of Psychiatry, Clinical Research Centre, Watford Road, Harrow, Middlesex HA1 3UJ, UK

Measurement of the alpha-cell-migration in the entorhinal region: A marker for the developmental disturbances in schizophrenia? : P. Falkai∗, B. Bogerts∗, G.W. Roberts∗∗ and T.J. Crow∗∗ ∗Department of Psychiatry, University of Düsseldorf, Bergische Landstrasse 2, 4000 Düsseldorf 12, FRG; and ∗∗Division of Psychiatry, Clinical Research Centre, Watford Road, Harrow, Middlesex HA1 3UJ, UK