Salience and target selection in visual search

Abstract

Why is it easy to find strawberries and difficult to collect gooseberries or green tomatoes? Why don't we see the tree in the forest but do see the single tree in the garden? Various explanations have been given to account for these phenomena. The present paper is concentrating on salience, a property apparently important for search but not frequently discussed in this context. Salience lets targets stand out and thus controls the selection of items that need to be investigated when a certain target is to be searched for. This proposal was tested in two series of experiments. It was found that salience detection and target identification followed different time courses; even typical “pop-out” targets (bright or dark blobs, gaps) were faster located than identified. The importance of salience in visual search was further investigated by manipulating target salience without affecting stimulus properties that are assumed to be relevant for search. When the salience of individual items was increased, the effective set size was reduced and search performance improved. This suggests an interactive and complementary function of salience and attention which is further discussed.

Acknowledgments

I am very grateful to J. R. Pomerantz and an anonymous referee for helpful comments.

Notes

¹In this particular example, the difference in salience is very large and could indeed be described in the pop-out terminology: One target pops out; the other doesn't. However, graded differences in salience may be important in other examples.

²There are numerous explanations of why a certain target pops out or does not. In the feature-search model (e.g., Treisman, 1985), for example, the left-hand target is assumed to be immediately detected because one of its features (vertical) is preattentively processed. In a different view the target is salient because it differs in orientation from that of neighbouring bars (Nothdurft, 1992). The issue of the present paper, however, goes beyond such a distinction. It argues that salience itself, however it is produced, is a major key in fast visual search.