Negative and Positive Congruence Effects in Letters and Shapes
Perception & Psychophysics 2004, 66 (6), 908-925 Negative and positive congruence effects in letters and shapes CEES VAN LEEUWEN Brain Science Institute, RIKEN, Wako-Shi, Japan and University of Sunderland, Sunderland, England and THOMAS LACHMANN University of Leipzig, Leipzig, Germany, and Brain Science Institute, RIKEN, Wako-Shi, Japan In six experiments in which a binary classification task was used, letter and nonletter (geometrical shapes, pseudoletters, or rotated letters) targets were presented either in isolation or surrounded by a geometrical shape. The surrounding shape could be congruent or incongruent with the target. When the classification required a distinction between letters and nonletters, either explicitly (Experiments 1–3) or implicitly (Experiment 4), a negative congruence effect was obtained for letters, contrasting with a regular, positive congruence effect for nonletters. When no distinction was to be made, letters and non- letters invariably showed a positive congruence effect (Experiments 5 and 6). In particular, between Ex- periments 1–4 and Experiments 5 and 6, the occurrence of negative or positive congruence effects for the same stimuli depended on the task. Feature interaction, target selection, and response competition explanations were tested against a feature integration approach. The results are explained in terms of different feature integration strategies for letters and nonletters. Intrinsic stimulus characteristics alone fail to determine It may seem as if the experimental literature has yet to what is easy or hard to perceive; this depends on the task discover the task dependency of irrelevant surrounding or as well. It is easy, for instance, to perceive the geometrical flanking information in perception. Flanking effects, es- structure in Figure 1A due to its saliency, but this very pecially in peripheral vision when the distractor informa- saliency makes it difficult to identify the letter E in the tion is very close, are attributed to insufficient resolution figure.
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