Biomedical subjects

W Notebaert

Publications and source records attributed to W Notebaert.

3 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↗

PubMed1998

Lorazepam but not diazepam impairs identification of pictures on the basis of specific contour fragments.

We tested the effects of lorazepam 0.038 mg/kg and diazepam 0.3 mg/kg on the identification of pictures of everyday objects that were specifically modified to examine the role of different parts of the external contour. By pressing the space bar of a computer keyboard, observers could add 1% of the total contour of each picture until it was recognized. Identification thresholds were measured in three display conditions, depending on where along the contour the addition of contour pixels started. In the minima condition, stimuli were initially displayed with only minima (i.e., locations along the contour where negative curvature is strongest); all parts with negative curvature were then built up gradually from the minima and only later on were the fragments with positive curvature shown until the contour became closed at the maxima (i.e., locations where positive curvature is strongest). In the maxima condition, initially only the maxima were displayed, with all positive contour built up first and then the negative curvature until the minima were reached. In the inflections condition, the points along the contour shown first were inflections (i.e., points where curvature is locally zero because the sign of curvature changes there) and contour was built up by adding parts of positive and negative curvature at both sides of each inflection until the extrema (minima and maxima) were reached to close the contour of the picture. In general, picture identification was more difficult (i.e., a larger portion of the contour was required) in the minima condition than in the maxima and the inflections conditions. The diazepam group did not differ significantly from the placebo group, while the lorazepam group had significantly lower performance in all three display conditions. Results are discussed in relation to previous research showing impaired perceptual integration and impaired implicit memory under lorazepam influence.

Adult↗