Abstract
Adaptation to facial characteristics, such as gender and viewpoint, has been shown to both bias our perception of faces and improve facial discrimination. In this study, we examined whether adapting to two levels of face trustworthiness improved sensitivity around the adapted level. Facial trustworthiness was manipulated by morphing between trustworthy and untrustworthy prototypes, each generated by morphing eight trustworthy and eight untrustworthy faces, respectively. In the first experiment, just-noticeable differences (JNDs) were calculated for an untrustworthy face after participants adapted to an untrustworthy face, a trustworthy face, or did not adapt. In the second experiment, the three conditions were identical, except that JNDs were calculated for a trustworthy face. In the third experiment we examined whether adapting to an untrustworthy male face improved discrimination to an untrustworthy female face. In all experiments, participants completed a two-interval forced-choice (2-IFC) adaptive staircase procedure, in which they judged which face was more untrustworthy. JNDs were derived from a psychometric function fitted to the data. Adaptation improved sensitivity to faces conveying the same level of trustworthiness when compared to no adaptation. When adapting to and discriminating around a different level of face trustworthiness there was no improvement in sensitivity and JNDs were equivalent to those in the no adaptation condition. The improvement in sensitivity was found to occur even when adapting to a face with different gender and identity. These results suggest that adaptation to facial trustworthiness can selectively enhance mechanisms underlying the coding of facial trustworthiness to improve perceptual sensitivity. These findings have implications for the role of our visual experience in the decisions we make about the trustworthiness of other individuals.
Highlights
Prolonged exposure to a visual stimulus can alter the tuning of neurons that encode that stimulus by a process known as adaption (Barlow and Hill, 1963)
EXPERIMENT 1 Experiment 1 measured the effects of adaptation to untrustworthy (80) and trustworthy (40) female faces on discrimination thresholds around an untrustworthy female face (80)
Planned pair-wise comparisons confirmed that just-noticeable differences (JNDs) were smaller when adapting to an untrustworthy face compared to either adapting to a trustworthy face (p < 0.05), or no adaptation (p < 0.05)
Summary
Prolonged exposure to a visual stimulus can alter the tuning of neurons that encode that stimulus by a process known as adaption (Barlow and Hill, 1963). After adapting to a leftward moving grating, subsequently viewed gratings can appear to move in a rightward direction These perceptual biases, known as aftereffects, have been demonstrated following adaptation to stimuli as diverse as orientation (Gibson and Radner, 1937), speed (Goldstein, 1957), contrast (Ross et al, 1993), spatial frequency (Blakemore and Campbell, 1969), facial configuration (Webster and MacLin, 1999), biological motion (Jordan et al, 2006; Troje et al, 2006), actions (Barraclough et al, 2009), and complex natural scenes (Greene and Oliva, 2010). This differential sensitivity increases as a function of adaptation duration, allowing us to detect even smaller differences to stimuli to which we are commonly exposed (Clifford and Langley, 1996)
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