Elsevier

Cognition

Volume 96, Issue 1, May 2005, Pages B33-B43
Cognition

Brief Article
Horizontal and vertical Simon effect: different underlying mechanisms?

https://doi.org/10.1016/j.cognition.2004.11.009Get rights and content

Abstract

Reaction times are usually faster when stimulus and response occur at the same location than when they do not, even if stimulus location is irrelevant to the task (Simon effect). This effect was found with both horizontal and vertical stimulus-response arrangements. The same mechanisms have been proposed to be involved in either case. Here, we compared a horizontal and a vertical Simon task by means of a RT time-course analysis of the Simon effect. Also, we analysed the lateralised readiness potential (LRP), an index of covert response-preparation processes. In the horizontal task, the Simon effect decays over time and pre-activation occurs above the motor cortex ipsilateral to the stimulus. In contrast, the Simon effect does not decay over time and no early incorrect LRP deflection is observed in the vertical task. These findings suggest that typical activation accounts can fit only the horizontal Simon effect, while a translation explanation is more suitable for the vertical Simon effect.

Section snippets

Participants

Ten volunteer healthy participants (seven males; mean age: 34±10) took part to the experiment. All were right-handed, had normal or corrected-to-normal visual acuity, and were naive as to the purpose of the experiment.

Apparatus and stimuli

A Compaq 80386 Proline interfaced to a 14 in. monitor controlled stimuli presentation and behavioural data collection. The head was positioned in an adjustable head-and-chin rest. Distance between the eyes and the screen was 80–85 cm. Target stimuli were 4×4 red-and-black or

RTs

Mean correct RTs and percentage of correct responses are shown in Table 1. Behavioural data were submitted to repeated measures analyses of variance (ANOVAs). The first ANOVA compared RTs in the two tasks. This analysis had two within-subjects variables: target-response correspondence (corresponding vs. non-corresponding trials) and task (horizontal vs. vertical). The two main effects were significant [F(1, 9)=41.3, P<0.001 for correspondence, and F(1, 9)=8.2, P<0.05 for task]. The main effect

Discussion

The differences between horizontal and vertical tasks suggest the existence of different underlying mechanisms. Although the regular analysis on mean RTs did not show any difference in the magnitude of the Simon effect, the distributional analysis revealed a substantially different time-course of the two effects. In the horizontal task the Simon effect decreased as RT increased in accord with the findings of previous studies (e.g. Rubichi et al., 1997), whereas in the vertical task the Simon

Acknowledgements

The authors thank Raffaele Orsato for helpful suggestions. This research was supported in part by grants from MIUR and from the University of Padua to Carlo Umiltà.

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