Biomedical subjects

E Soetens

Publications and source records attributed to E Soetens.

9 recordsLinked to original sources

PubMed2004

Sequence learning and sequential effects.

In a serial reaction time (RT) task with a probabilistic stimulus sequence, the length of the response-to-stimulus interval (RSI) and the sequence complexity was manipulated to investigate the relationship between sequence learning and sequential effects in serial RT tasks. Sequential effects refer to the influence of previous stimulus presentations on the RT to the current stimulus. Sequence learning is stimulus-transition specific and is demonstrated as the difference between practiced and unpracticed sequences within an interpolated random block of trials. There is a clear parallel between sequence learning and specific changes in sequential effect in the short RSI conditions, suggesting that a common mechanism may lie at the basis of sequence learning and automatic facilitation, which is responsible for sequential effects at short RSI. Importantly, the changes in sequential effects accompanying sequence learning are the same as those observed with practice in random serial RT tasks, indicating that the learning process underlying sequence learning is the same as in random tasks.

Adolescent↗

PubMed2001

Sequential analysis of a Simon task--evidence for an attention-shift account.

We investigated the attention-shift hypothesis of the Simon effect by analysing the effect of repeating relevant colour or irrelevant location of the stimulus in four serial reaction time tasks. In Experiment 1 with short response-stimulus intervals (RSI), we assume that there is no time to engage attention at the fixation cross before the onset of a new stimulus. In agreement with the hypothesis, Experiment 1 reveals no Simon effect when the stimulus location is repeated. In Experiment 2 with long RSI, we observe a Simon effect for location repetitions and alternations. In Experiment 3 with long RSI, we hinder the disengagement of attention by displaying the stimulus after response execution. As expected, the Simon effect is reduced for location repetitions. In Experiment 4 with stimuli additionally presented at the fixation cross, responses are faster if the attention shift towards the centrally presented stimulus corresponds with the location of the required response. Additionally, we argue that binding of the stimulus features into an object or event file better explains the so-called blocking of the automatic response-priming route after a noncorresponding trial.

Attention↗

PubMed1999

Effects of oral administration of the competitive N-methyl-D-aspartate antagonist, CGP 40116, on passive avoidance, spatial learning, and neuromotor abilities in mice.

The effects were investigated of the potent competitive N-methyl-D-aspartate (NMDA) receptor antagonist CGP 40116[D-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid] on the performance of mice in water maze and passive avoidance tasks, and in wire suspension, rotarod, and cage activity tests. The drug was administered per os (p.o.) in its anticonvulsant dose range. CGP 40116 dose-dependently impaired passive avoidance learning when given before, but not when given after training. The antagonist (5, 10, and 20 mg/kg, administered 4 h before each training session) dose-dependently affected water maze acquisition, and impaired retention test performance in both hidden- and visible-platform water maze tasks. In addition, the drug dose-dependently decreased swimming speed during water maze acquisition. Repeated administration of CGP 40116 (20 mg/kg, p.o.) persistently decreased cage activity and wire suspension test performance, whereas motor coordination and equilibrium on the rotarod apparatus remained unimpaired. In our administration protocol, no tolerance was found to the effects of the drug on passive avoidance learning and neuromotor abilities. The parallel effects of CGP 40116 on memory and motor performance are discussed, and it was concluded that the antagonist impairs neuromotor abilities and also induces memory impairments which cannot be entirely reduced to motor interference.

2-Amino-5-phosphonovalerate↗

PubMed1999

Covert signs of expectancy in serial reaction time tasks revealed by event-related potentials.

Choice reaction time is strongly determined by the sequence of preceding stimuli. With long response-stimulus intervals (RSIs), a cost-benefit pattern is observed, which has been related to expectancy, whereas with short RSIs a benefit-only pattern emerges, possibly because of automatic facilitation. In the present study, event-related potentials were recorded while subjects performed serial choice responses to visual and auditory stimuli at long and short RSIs. As expected, reaction times displayed cost-benefit and benefit-only patterns at long and short RSIs, respectively. In contrast, sequential effects in event-related potential amplitudes displayed a cost-benefit pattern, unaffected by the RSI. The results demonstrate that an expectancy-like mechanism is always active in serial tasks but appears to influence performance only when the RSI is long.

Adult↗

PubMed1995

No influence of ACTH on maximal performance.

Although it is generally accepted in the sporting world that adrenocorticotropic hormones (ACTH) and corticosteroids enhance maximal performance, this claim has never been scientifically corroborated. In a counterbalanced, double-blind design, 1 mg ACTH or placebo was injected into 16 professional cyclists. They cycled for 1 h on a bicycle ergometer at a submaximal level, defined as 60% of maximal performance on a pretest with a load increase of 50 W per minute. After 1 h, load was increased by 10 W per minute until exhaustion. No increase of maximal performance was observed with ACTH, either on the day of drug intake, or on the following day, although substantial increases were measured in physiological variables such as cortisol, glucose, and white corpuscle concentrations. Feelings of fatigue, which were continuously self-rated, were diminished only during submaximal performance. The present technique of systematically distinguishing between physiological, psychological, and performance measurements could help in explaining the persistent belief in the performance enhancing properties of ACTH and other doping substances.

Adrenocorticotropic Hormone↗

PubMed1995

Effect of amphetamine on long-term retention of verbal material.

A series of five experiments was conducted to investigate the temporal aspects of human memory consolidation of symbolic material through the administration of amphetamine. Subjects had to recall or recognise unrelated words from a previously presented list. The first experiments support the conjecture, based on animal studies, that amphetamine enhances long-term memory performance. Subsequently, enhancement is demonstrated with oral administration before learning, as well as with intramuscular injection after learning. It is shown that improved recall cannot be explained solely by general arousal or attentional processes, but must be due to consolidation. By introducing different test delays we show that consolidation of symbolic material can be modulated by amphetamine during the 1st hour after learning. In a final experiment we demonstrate that the memory enhancement applies to recall as well as to recognition. The implications of the present results are discussed in the context of recent research on LTP processes.

Administration, Oral↗

PubMed1993

Amphetamine enhances human-memory consolidation.

Although it is generally accepted that CNS stimulants have enhancing effects on long-term storage processes in laboratory animals, little is known about their influence on human learning. We report a series of experiments with free recall of lists of unrelated words, demonstrating a significant enhancement on long-term retention after amphetamine administration. A gradual increase of recall was observed up to 1 h after learning, remaining stable for at least 3 days, after oral administration before learning as well as intramuscular injection after learning. The results show that research on humans with drug-induced memory-enhancement techniques is necessary to supplement the animal studies for the understanding of the mechanisms involved in information consolidation.

Amphetamine↗

PubMed1984

Automatic aftereffects in two-choice reaction time: a mathematical representation of some concepts.

A mathematical model is developed to describe sequential effects in two-choice reaction time experiments with a short response-stimulus interval. Evidence is briefly discussed that in conditions with short response-stimulus intervals, automatic aftereffects dominate sequential effects, and the influence of subjective expectancy can be neglected. In these conditions the model premises three components of automatic aftereffects--facilitation, inhibition, and noise, with a common decay factor. Influence of response-stimulus interval and practice on sequential effects are examined and related to parameter changes in the proposed single-decay model. The decrease of automatic aftereffects with increasing response-stimulus interval is primarily ascribed to an increasing decay factor. The parameter representation of the model also clarifies the issue of the disappearance of automatic aftereffects with practice. It shows a gradual fading of inhibition in the initial stages of practice, together with a slower decrease of the facilitation effect. The single-decay model provides a satisfactory explanation for the processes involved in compatible two-choice reaction time with short response-stimulus interval.

Choice Behavior↗

PubMed1981

Perception of memorized works and nonwords.

In this experiment we tried to explain why a word is perceived more accurately than a nonword. We compared the accuracy of the tachistoscopic recognition of words with memorized words and of nonwords with memorized nonwords. We used the method of the critical interstimulus interval (Turvey, 1973). The results showed that the over-all performance was better in the word conditions than in the nonword conditions, but the influence of the memorizing factor was virtually nonexistent. This is in contradiction with two proposed hypotheses, the "feature redundancy theory" because the memorizing factor was not significant and Massaro's (1973) assumptions that the difference between words and nonwords is due to redundancy. Although words and nonwords were equated for redundancy, there remained a difference in processing time. Words and nonwords seem to be processed in essentially different ways. The word advantage seems to be dependent upon the subjects' strategy to consider the presented words as a whole.

Discrimination Learning↗