Visual Awareness and the Detection of Fearful Faces Luiz Pessoa Brown University Shruti Japee and Leslie G. Ungerleider National Institute of Mental Health A commonly held view is that emotional stimuli are processed independently of awareness. Here, the authors parametrically varied the duration of a fearful face target stimulus that was backward masked by a neutral face. The authors evaluated awareness by characterizing behavioral performance using receiver operating characteristic curves from signal detection theory. Their main finding was that no universal objective awareness threshold exists for fear perception. Although several subjects displayed a behavioral pattern consistent with previous reports (i.e., targets masked at 33 ms), a considerable percentage of their subjects (64%) were capable of reliably detecting 33-ms targets. Their findings suggest that considerable information is available even in briefly presented stimuli (possibly as short as 17 ms) to support masked fear detection. Emotional stimuli, such as a picture of a fearful face or an aversive scene, are processed rapidly. For example, when viewing such pictures, subjects exhibit fast, involuntary, autonomic re- sponses (Ohman, Esteves, & Soares, 1995). Under some condi- tions, the processing of emotional stimuli may proceed when the stimuli are outside the focus of attention (Vuilleumier, Armony, Driver, & Dolan, 2001). Consistent with the view that the stimuli are processed preattentively, the detection of threat-related stimuli (e.g., a snake) is associated with relatively flat search slopes in visual search tasks (Ohman, Flykt, & Esteves, 2001). Many inves- tigators have proposed that not only is the processing of emotional stimuli somewhat independent of attention but that it can take place without reaching conscious awareness. Evidence for this view comes from studies showing both skin conductance and neuroimaging responses to briefly presented and masked stimuli that subjects were apparently unaware of (Morris, Ohman, & Dolan, 1998; Ohman et al., 1995; Whalen et al., 1998). Taken together, the view has emerged that emotional (especially nega- tive) stimuli are processed in a largely automatic fashion, which is independent of attention and awareness. Brief presentation and backward masking have been used to manipulate awareness during the viewing of emotional stimuli. A strategy devised by Ohman and colleagues (Esteves & Ohman, 1993) is widely used for masking emotional faces. An initial emotional target face is presented for a brief duration, typically around 30 ms, and is immediately followed by a neutral face that is shown for a slightly longer duration, typically 50 ms or more. Under such conditions, it is widely believed that emotional faces are effectively masked because subjects exhibit chance levels of performance at detecting the target face (e.g., Morris et al., 1998) or because they report not having seen the stimuli on subsequent debriefing (e.g., Whalen et al., 1998). However, in the past, chance performance has been assessed by determining percentage correct values, which are known to be highly sensitive to response bias (Green & Swets, 1966; Macmillan & Creelman, 1991). In the face of weak, noisy signals, subjects may often indicate not detecting target stimuli and thus appear to be unable to reliably detect them. Determining the stimulus parameters associated with aware and unaware perception is important because these modes of percep- tion are routinely linked to brain activations in neuroimaging studies. Thus, understanding the extent to which the processing of emotional perception takes place automatically necessitates the careful characterization of those viewing conditions leading to aware or unaware perception. Visual awareness can be characterized by both objective and subjective criteria (Merikle, Smilek, & Eastwood, 2001; Snodgrass, Bernat, & Shevrin, 2004). Much conceptual and em- pirical debate centers on the question of the relative merits of the two criteria, with polarized views favoring both methodologies. In the present study, we assessed awareness according to objective criteria by having subjects perform a forced-choice fear-detection task. Performance was evaluated according to standard signal- detection theory methods, which provide a measure of sensitivity that is independent of a subject’s response bias (Green & Swets, 1966; Macmillan & Creelman, 1991). We parametrically varied the duration of an emotional target stimulus and characterized behavioral performance with receiver operating characteristic (ROC) curves. In this manner, we determined whether subjects could (objectively aware) or could not (objectively unaware) reli- ably detect briefly presented and masked fearful faces. Method Eleven volunteers (6 women) aged 25.4  5.2 years participated in the study, which was approved by the National Institute of Mental Health Institutional Review Board. All subjects were in good health with no past history of psychiatric and neurologic disease and gave informed consent. Subjects had normal or corrected-to-normal vision. Luiz Pessoa, Department of Psychology, Brown University; Shruti Japee and Leslie G. Ungerleider, Laboratory of Brain and Cognition, National Institute of Mental Health, Bethesda, Maryland. This study was supported in part by the National Institute of Mental Health—Intramural Research Program. Luiz Pessoa is supported in part by National Institute of Mental Health Grant 1 R01 MH071589-01. We thank Richie Davidson and Jeffrey Maxwell for comments on the manuscript and Alumit Ishai for making available a set of emotional faces. Correspondence concerning this article should be addressed to Luiz Pessoa, Department of Psychology, Brown University, 89 Waterman Street, Providence, RI 02912. E-mail: pessoa@brown.edu Emotion Copyright 2005 by the American Psychological Association 2005, Vol. 5, No. 2, 243–247 1528-3542/05/$12.00 DOI: 10.1037/1528-3542.5.2.243 243