The ability to distinguish between confusable expressions has been assessed with tests such as the Emotion Hexagon Test ( Young et al., 2002), which requires participants to name the emotional term that best describes images composed of graded blends of two confusable emotional expressions (such as happiness and surprise and disgust and anger).ĭespite the interest in the ability to identify and to distinguish facial expressions of emotion, the basic perceptual abilities that may assist the more complex processes of identifying a specific emotion by name and distinguishing between emotions remain less explored.

There has also been interest in using dynamic morphed stimuli (from an emotional face to a neutral face, and from one emotion to another) to measure the point at which an emotion becomes apparent from a neutral expression and at which a change in emotion is detected ( Niedenthal et al., 2000, 2001 Montagne et al., 2007 Fiorentini and Viviani, 2011 Sacharin et al., 2012). There has been some interest in the ability to identify graded intensities of facial expressions of emotion with rating scales ( Matsumoto et al., 2000 Dujardin et al., 2004). In everyday life, however, emotions are generally expressed with graded intensity. The stimuli used in identification studies generally depict full-blown emotional facial expressions selected from validated stimulus sets ( Matsumoto and Ekman, 1988 Tottenham et al., 2009). The Ekman 60 Faces Test ( Young et al., 2002) exemplifies a recognition test that requires participants to select from a list of six basic emotions the emotion that best describes the facial expression shown. Much of this research has focused on the ability to recognize facial expressions of emotion, usually assessed as the ability to identify specific emotions by name (retrieved either from memory or a list of names) or to distinguish different expressions of emotion ( Calder et al., 2000 Matsumoto et al., 2000 Clark et al., 2008 Young and Hugenberg, 2010 Bell et al., 2011). Emotion perception has been studied in different populations including children ( Gao and Maurer, 2009), young adult ( Elfenbein and Ambady, 2002), and the aging ( Sullivan and Ruffman, 2004), and in both healthy and clinical populations ( Montagne et al., 2007 Assogna et al., 2008 Hippolyte et al., 2008 Hofer et al., 2009 Harms et al., 2010). The ability to perceive the facial expressions of emotion of others is central to the regulation of social behavior. The tasks give objective and sensitive measures of the basic perceptual abilities required for perceiving and interpreting emotional facial expressions. Individual data points were fitted by Quick functions for each task and each emotion, allowing estimates of absolute thresholds and slopes. Psychometric functions were obtained for 15 healthy young adults using the Method of Constant Stimuli with a two-interval forced-choice procedure. The stimuli were created by morphing photographs of models expressing four basic emotions, anger, disgust, happiness, and sadness with neutral expressions. We report the development of two simple, objective, psychophysical measures of the ability to discriminate facial expressions of emotion that vary in intensity from a neutral facial expression and to discriminate between varying intensities of emotional facial expression. 2Department of Psychology, Curtin University, Perth, WA, Australia.1Department of Psychology, The University of Western Australia, Perth, WA, Australia.Michelle Marneweck 1*, Andrea Loftus 2 and Geoff Hammond 1

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