Developing the Leuven Embedded Figures Test (L-EFT): Testing the stimulus features that influence embedding

Background. The Embedded Figures Test (EFT, developed by Witkin and colleagues (1971)) has been used extensively in research on individual differences, particularly in the study of autism spectrum disorder. The EFT was originally conceptualized as a measure of field (in)dependence, but in recent years performance on the EFT has been interpreted as a measure of local versus global perceptual style. Although many have used the EFT to measure perceptual style, relatively few have focused on understanding the stimulus features that cause a shape to become embedded. The primary aim of this work was to investigate the relation between the strength of embedding and perceptual grouping on a group level. Method. New embedded figure stimuli (both targets and contexts) were developed in which stimulus features that may influence perceptual grouping were explicitly manipulated. The symmetry, closure and complexity of the target shape were manipulated as well as its good continuation by varying the number of lines from the target that continued into the context. We evaluated the effect of these four stimulus features on target detection in a new embedded figures task (Leuven Embedded Figures Test, LEFT) in a group of undergraduate psychology students. The results were then replicated in a second experiment using a slightly different version of the task. Results. Stimulus features that influence perceptual grouping, especially good continuation and symmetry, clearly affected performance (lower accuracy, slower response times) on the L-EFT. Closure did not yield results in line with our predictions. Discussion. These results show that some stimulus features, which are known to affect perceptual grouping, also influence how effectively a stimulus becomes embedded in different contexts. Whether these results imply that the EFT measures individual differences in perceptual grouping ability must be further investigated.

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