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PubMed2000

Sequential effects in number comparison.

The modular framework of number processing (e.g., S. Dehaene & R. Akhavein, 1995) was applied to study sequential trial-to-trial effects in a number comparison task. In Experiment 1, numbers were always presented as digits. Responses were faster when the same number was repeated, but this effect was additive with the numerical distance effect. In Experiment 2, numbers were presented either as digits or as words. The authors found significant effects of repeating (a) the same physical stimulus, (b) the same number but in a different notation, and (c) the same notation but a different number. Again, all 3 effects were additive with the numerical distance effect. The authors' results provide strong evidence against accounts according to which, on stimulus repetition trials, the comparison stage is bypassed (as proposed by S. Dehaene, 1996), and the results clearly favor an early, precomparison locus of repetition effects.

Adolescent↗

PubMed1994

Coactivation and statistical facilitation in the detection of lines.

The redundant-signals effect describes the general phenomenon that simple reaction times to two simultaneously presented signals are typically faster than the corresponding reaction times to each of the signals presented alone. Recent studies (eg Miller 1982, 1986) indicate that models of probability summation in which an independent detection of both signals is assumed cannot completely account for the observed shortening of the reaction times. Therefore, models in which some kind of coactivation is assumed are often considered as an alternative explanation. In the present study simple reaction times to parallel lines are compared with those to orthogonal lines and single lines. Our first hypothesis is that because of the redundant-signals effect, the reaction time to configurations consisting of two lines (either parallel or orthogonal) will generally be faster than the reaction time to a single line. Furthermore, line detection can be related to orientation-specific line detectors. Therefore, parallel lines may be thought to activate similar line detectors and, by coactivation, facilitate detection. As our second hypothesis we thus expect that the reaction time to parallel lines will be shorter than the reaction time to orthogonal lines. To test these hypotheses, we conducted a simple reaction-time experiment in which signal onset asynchronies ranging from 0 to +/- 56 ms for the orthogonal lines were used. In addition, reaction times to parallel lines and single lines were measured. Both hypotheses are supported by our data. We formulate a stochastic model which is able to explain both statistical facilitation and coactivation in a physiologically plausible way.

Adult↗