Modulation of the vertical Simon effect in two-dimensional tasks: The effect of learning

The study supports the relative salience account by showing that manipulating relative salience of one dimension affects the magnitude of the Simon effect in that dimension. However, there was also evidence of a true right-left prevalence, in that the Simon horizontal was greater than the Simon vertical and the Simon VE was affected by manipulation of the salience of the vertical dimension, whereas the Simon HE was not. We reasoned that performing a vertical spatial compatibility task before the two-dimensional Simon task should render the vertical dimension more salient and thus increase the magnitude of the Simon VE. In accordance with this prediction, the Simon VE increased from 6 ms (non-significant), when subjects performed the two-dimensional Simon task only, to 18 ms (significant), when subjects performed the two-dimensional Simon task after the vertical spatial compatibility task. The pattern shown by the Simon HE was markedly different: It was greater than the Simon VE (26 ms, significant), when only the two-dimensional Simon task was performed, and did not change (22 ms, significant), when the two-dimensional Simon task was preceded by the vertical spatial compatibility task. In conclusion, it seems that the relative salience hypothesis put forward by Vu et al. (2000) is basically correct. However, there is also a right-left dominance that is yet in need of being explained.

The present work was aimed at investigating whether automatic two-dimensional spatial coding, as indexed by the Simon task, is affected by prior practice with a vertical spatial compatibility task. One group of subjects performed a two-dimensional Simon task in which the vertical Simon effect was absent. The other group practised the vertical dimension by performing a vertical spatial compatibility task before the two-dimensional Simon task. With prior practice, the vertical Simon effect was significant. These results are discussed in the framework of the factors that affect two-dimensional spatial coding.