At first sight: a high-level pop out effect for faces

To determine the nature of face perception, several studies used the visual search paradigm, whereby subjects detect an odd target among distractors. When detection reaction time is set-size independent, the odd element is said to "pop out", reflecting a basic mechanism or map for the relevant feature. A number of previous studies suggested that schematic faces do not pop out. We show that natural face stimuli do pop out among assorted non-face objects. Animal faces, on the other hand, do not pop out from among the same assorted non-face objects. In addition, search for a face among distractors of another object category is easier than the reverse search, and face search is mediated by holistic face characteristics, rather than by face parts. Our results indicate that the association of pop out with elementary features and lower cortical areas may be incorrect. Instead, face search, and indeed all feature search, may reflect high-level activity with generalization over spatial and other property details.