Biomedical subjects

J H R Maes

Publications and source records attributed to J H R Maes.

12 recordsLinked to original sources

PubMed2006

Learned irrelevance and response perseveration in a total change dimensional shift task.

Thirty-six healthy participants received a discrimination learning task requiring the identification of a relevant stimulus dimension. After successful learning, the relevant dimension was shifted unannounced. All exemplars of the two dimensions presented after the shift were novel, implying a 'total change' design. In three experimental conditions, participants could either make only errors reflecting perseveration of responding to the former relevant dimension, continued ignoring of the former irrelevant dimension, or both. After the shift, the participants in the perseveration condition made fewer errors than did those in the other two conditions, which did not differ. These results imply a predominance of the learned irrelevance mechanism even when any direct transfer of learning about exemplars in the pre-shift phase is precluded.

Adult↗

PubMed2006

Processing of emotionally toned pictures in dementia.

BACKGROUND: Apathy is a common symptom in dementia and is often associated with reduced emotional reactivity. This study examined whether reduced emotional reactivity can be demonstrated in dementia patients using a picture viewing task. METHODS: The viewing time of three different types of visual stimuli was measured in 24 elderly participants, half of which suffered from dementia. The participants had to make a target response to an emotionally neutral target stimulus that was intermixed with a frequently occurring non-target or 'background' stimulus and infrequently presented emotional stimuli. All participants could control the presentation time of each stimulus, but one half of the participants were explicitly instructed to perform the task quickly. RESULTS: The main measure was a ratio score in which the viewing time for emotional stimuli was expressed relative to the viewing time for the neutral non-target stimulus. Using this measure, the instigation of a time-pressure condition proved to significantly reduce the viewing time for emotional stimuli in the healthy subjects. Irrespective of time-pressure condition, the dementia patients showed a similar short viewing time for emotional stimuli as did the healthy subjects in the time-pressure condition. However, both dementia patients and healthy controls displayed longer viewing times for unpleasant than for pleasant stimuli. CONCLUSION: These results suggest the ability of the present task to reveal the simultaneous occurrence of an overall reduced interest for novel stimuli and an intact differential emotional reactivity to stimuli with a negative versus positive valence in the dementia patients.

Aged↗

PubMed2006

Response bias induced in rats by response effects.

Two experiments examined whether response choice in rats is affected by the presentation of response-produced stimuli. Rats were first trained to emit two different responses, with each response producing a unique auditory stimulus. Subsequently, the former response-produced stimuli were presented while the two response options were freely available. Presentation of a former response-produced stimulus caused the rats to choose more frequently the response option that had previously produced that specific stimulus over the other response option. However, although statistically significant, this response-biasing effect was numerically weak and was only apparent when the stimuli no longer had a general response-activating effect. Moreover, in the case of relatively short presentations of the stimuli, the response-biasing effect was only present if, during testing, the responses continued to produce the auditory stimuli according to the response-effect mapping used during training. These results were discussed in terms of possible underlying associations and were contrasted with previous results from analogous human studies on action control by response-produced stimuli.

Analysis of Variance↗

PubMed2004

With long intervals, inter-stimulus interval is the critical determinant of the human P300 amplitude.

Previous research, using short inter-stimulus intervals (1-4 s), suggests that the P300 of the human event-related potential during oddball and single-stimulus tasks is mainly affected by target-to-target interval (TTI). The present study tested the validity of this claim at longer intervals in a learning task. Participants were assigned to either an oddball task with an inter-stimulus interval (ISI) of 9-20 s or a single-stimulus task with an ISI of 9-20 or 40-90 s and had to learn when to respond to the stimuli. In the oddball task, the target elicited larger amplitudes than did the standard. When comparing the stimuli from the short- and long-ISI conditions with the target from the oddball condition, it was found that the P300 was more positive at long-ISI stimuli than at short-ISI stimuli or oddball targets, and short-ISI stimuli and oddball targets elicited equally large P300 amplitudes. These results suggest that, in oddball tasks with long intervals, besides cognitive factors, ISI rather than TTI affects the P300 amplitude.

Adaptation, Physiological↗

PubMed2004

Enhanced re-habituation of the orienting response of the human event-related potential.

Previous studies found the amplitude of the orienting response (OR) of the human event-related potential to decrease with repeated stimulus presentations. This decrease has been suggested to reflect short-term habituation and/or long-term habituation, both of which are learning processes. However, this earlier research failed to provide direct evidence supporting this claim. The present study attempted to show that the OR pattern shares one important feature of habituation: an enhanced response decrement across stimulus-presentation blocks (enhanced re-habituation). Participants received four blocks of 25 auditory stimulus presentations and showed an OR decrement both within (short-term habituation) and across (long-term habituation) blocks. Importantly, the OR decreased more rapidly during later than initial trial blocks, suggesting enhanced re-habituation. The latter result supports the notion that the amplitude decrement reflects an elementary learning process.

Acoustic Stimulation↗

PubMed2004

More learned irrelevance than perseveration errors in rule shifting in healthy subjects.

The present experiments examined the extent to which two possible sources of error affect healthy subjects' performance in a rule-shift task. All 115 participants first received a discrimination learning task, in which a pair of different visual stimuli was presented on each trial, one of which had to be identified as 'correct.' Each stimulus varied in two dimensions: a task-relevant and a task-irrelevant dimension. Feedback on correctness was given after each choice. After eight successive correct choices, the nature of the task-relevant dimension changed: the post-shift learning phase. Two types of error can occur in this phase: continued responding to the former relevant, but now irrelevant, dimension, a perseverative error, and non-responding to the former irrelevant, but now relevant, dimension, an error due to learned irrelevance. Different groups received a post-shift task in which none, one, or both of these two types of error could affect performance. The number of incorrect choices in the post-shift phase was significantly affected by learned-irrelevance errors but not by perseverative errors. An associative-learning model incorporating feedback-induced changes in both associative strength and saliency of the elements comprising the stimuli can explain these results.

Adolescent↗

PubMed2004

Effects of stimulus repetitions on the event-related potential of humans and rats.

The present study compared the effects of repeated stimulus presentations on the event-related potential (ERP) of humans and rats. Both species were presented with a total of 100 auditory stimuli, divided into four blocks of 25 stimuli. By means of wavelet denoising, single-trial ERPs were established in both humans and rats. The auditory ERPs were characterized by the presence of two positive and two negative waves in both humans and rats, albeit with different latencies in the two species (P1, N1, P2, and N2). The results showed decreased amplitudes within blocks for the N1, P2, and N2 components in humans and for the N1 and P2 components in rats. Decreased amplitudes across blocks were found for the N2 component in humans and for the P2 and N2 components in rats. In both humans and rats, response decrements within a block were thus most prominent for the early ERP components, whereas the changes across blocks were most prominent for the later components. These results suggest a correspondence of the ERP correlates of elemental stimulus processing between humans and rats. It is further suggested that the observed amplitude reductions may reflect habituation and/or recovery cycle processes.

Acoustic Stimulation↗

PubMed2003

Auditory event-related potentials in humans and rats: effects of task manipulation.

The purpose of this study was to compare components of the rat and human auditory event-related potential (ERP) as generated in active oddball and passive single-stimulus tasks. The rats were trained to discriminate between target and standard stimuli in an oddball task, whereas the human subjects received instructions. Task effects on various ERP components were found in both species. Interestingly, effects on the P3 component were similar in the species with regard to amplitude: Target stimuli elicited a higher amplitude in the oddball task than did standard stimuli. This might indicate that the P3 shares the same characteristics between species. However, the first four components occurred 1.82 times earlier in rats than in humans, expecting a P3 of about 200 ms in rats. The P3 in rats appeared at 380 ms. We conclude that either the relation between human and rat peak latencies is not linear, or the P3 in rats is not the equivalent of the human P3.

Acoustic Stimulation↗

PubMed2003

Response stability and variability induced in humans by different feedback contingencies.

In two experiments, the behavioral effects of different response-feedback contingencies were examined with a task requiring human subjects to repeatedly type three-key sequences on a computer keyboard. In Experiment 1, the subjects first received positive feedback for response variability, followed by no feedback, or vice versa In Experiment 2, the subjects first received positive feedback for response variability, followed by response-independent positive feedback, or vice versa. Response stability and variability were examined using different measures, such as percentage of trials meeting the variability criteria, frequency of use of the different response alternatives, and autocorrelations as an index of response randomness. The subjects' behavior in the first phase in each condition came to reflect the current feedback contingency. Depending on the measure examined, responding after each contingency change was characterized by both response stability and decreases or increases in response variability. The collective results are discussed in the framework of previous animal and human studies on behavioral stability and variability.

Adult↗

PubMed2002

No sex difference in contextual control over the expression of latent inhibition and extinction in Pavlovian fear conditioning in rats.

Three experiments with Wistar rats searched for a sex difference in contextual control over the expression of latent inhibition and extinction. Experiment 1 used a latent inhibition procedure; Experiments 2 and 3 employed an extinction preparation. All experiments used a shock as the unconditioned stimulus, a tone as the conditioned stimulus, and suppression of food magazine visits as the measure of conditioned responding to the tone. Each experiment revealed a reliable context effect on conditioned responding to the tone; after conditioning in a separate context, conditioned responding in the former latent inhibition or extinction context was attenuated relative to conditioned responding in a control context. There was no sex difference in the magnitude of this effect. These results are discussed in the framework of sex differences in the hippocampus and of the putative role of this structure in various instances of contextual learning.

Acoustic Stimulation↗

PubMed2002

Contextual dependencies in a stimulus equivalence paradigm.

Two experiments with human subjects assessed contextual dependencies in a stimulus equivalence paradigm. Subjects learned to form two sets of stimuli in a matching-to-sample training procedure. Each set was presented against one of two different background colours, the contextual cues. At test, the influence of a context change-that is, presenting each set against the other context-was measured on baseline, symmetry, and equivalence trials. These three trial types reflect a difference in task complexity. It was predicted that the magnitude of context-dependent effects would be a positive function of task complexity. In Experiment 1, the context change was realized by switching the stimulus set at test while keeping the background colour constant. In Experiment 2, the stimulus set remained constant, and the background colour was switched. In both experiments, a change in context only resulted in an increase in response latency on equivalence trials; no effect was seen on symmetry and baseline trials. Results were discussed in the framework of switch costs, habituation to contextual stimuli, and a model based on Shea and Wright (1995) that explains the differential influence of a context switch on easy versus difficult tasks.

Adult↗

PubMed2002

Slow late component in conditioned stimulus-evoked potentials from the amygdala after fear conditioning in the rat.

Male Wistar rats were subjected to a differential Pavlovian fear conditioning procedure in which one of two tones (6 or 10 kHz) was followed by an electric shock (CS+) and the other was not (CS-). Before and after fear conditioning, we recorded the evoked potentials elicited by CS+ and CS- from electrodes aimed at the lateral nucleus of the amygdala. Before conditioning, a slow, negative component with peak amplitude around 150 ms was present in the evoked potentials. This component was sensitive to habituation. After fear conditioning, both CS+ and CS- elicited the same late component, albeit with a larger amplitude. This enhancement was temporary: decreasing amplitude was observed in the course of CS test presentations under extinction. Prior research revealed a comparable slow component in the amygdala of the cat under similar experimental conditions. The collective results indicate that the large late component in the amygdala is enhanced by fear conditioning, suggesting that such enhancement reflects the anticipation of a biologically significant event.

Acoustic Stimulation↗