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Nicholas Hedger, Wendy J. Adams, Matthew Garner; Fearful facial expressions are salient to early visual processes: evidence from effective contrast analyses and continuous flash suppression. . Journal of Vision 2014;14(10):1387. doi: 10.1167/14.10.1387.
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Neurocognitive models suggest that threat-relevant stimuli are prioritised in human vision by a specialised visual pathway that operates independently of conscious awareness (Tamietto & de Gelder, 2010). Findings from paradigms such as backward masking and continuous flash suppression (CFS) suggest that unconsciously presented fearful faces gain prioritised access to attentional resources (e.g. Carlson & Reinke, 2008; Fox, 2002) and awareness (e.g. Sylvers, Brennan & Lillenfeld, 2011; Yang, Zald & Blake, 2007). We ask whether this 'fear advantage', is driven by (i) an evaluation of the threat relevance of stimuli, that operates without awareness, or (ii) low-level image properties (e.g. contrast). Using human contrast sensitivity data, we estimated the effective contrast of fearful, angry, happy and neutral face stimuli as the ratio of stimulus contrast to detection threshold, across spatial frequency (e.g. Baker & Graf, 2009). Effective contrast was modulated by expression, with fear having the highest effective contrast, and anger the lowest. Critically, this pattern of modulation was an excellent predictor of dominance in a CFS paradigm; fear faces broke suppression most frequently, whereas anger faces broke suppression least often. Further analyses show that the higher effective contrast of fear faces is stable across a range of viewing distances, particularly those characteristic of typical human interactions. Our analyses suggest that our fearful facial expression is optimised in terms of its salience to the low-level visual mechanisms of human observers. We re-evaluate the evidence for unconscious processing of threat in the context of these image analyses, via a meta-analysis of visual probe and rivalry studies that report a 'fear advantage'. Effective contrast provides a simple, alternative explanation for some existing reports of a 'fear advantage' that negates the need to invoke unconscious processes that are sensitive to threat.
Meeting abstract presented at VSS 2014
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