The face-in-the-crowd effect: Threat detection versus iso-feature suppression and collinear facilitation

Are people biologically prepared for the rapid detection of threat posed by an angry facial expression, even when it is conveyed in the form of a schematic line drawing? Based on visual search times, the current literature would suggest that the answer is yes. But are there low-level explanations for this effect? Here, we present visual search results for schematic faces using current best practice, based on a concentric search array and set size manipulation. Using this approach, we replicate the classic search advantage for angry over happy faces. However, we also report a comparable effect when abstract plus- and square-shaped stimuli-derived from the angry and happy schematic faces respectively-are used within the same paradigm. We then go on to demonstrate that, while reduced, the effect remains after removal of the circular surround, bringing us closer to the source of the effect. We explore the possibility that the source of this search asymmetry could be the iso-feature suppression and collinear facilitation model proposed in Li's (1999a, 1999b, and 2002) bottom-up model of saliency. Simulations with this model using the abstract stimuli align with the corresponding behavioral results (i.e., the plus shape was found to be more salient than the square). Given the deliberate similarities between these abstract shapes and the respective face stimuli, we propose that the underlying cause for the asymmetries typically found using schematic faces, may be more related to early visual processing of line orientation than threat detection.