Inversion effects reveal dissociations in facial expression of emotion, gender, and object processing.

To distinguish between high-level visual processing mechanisms, the degree to which holistic processing is involved in facial identity, facial expression, and object perception is often examined through measuring inversion effects. However, participants may be biased by different experimental paradigms to use more or less holistic processing. Here we take a novel psychophysical approach to directly compare human face and object processing in the same experiment, with face processing broken into two categories: variant properties and invariant properties as they were tested using facial expressions of emotion and gender, respectively. Specifically, participants completed two different perceptual discrimination tasks. One involved making judgments of stimulus similarity and the other tested the ability to detect differences between stimuli. Each task was completed for both upright and inverted stimuli. Results show significant inversion effects for the detection of differences in facial expressions of emotion and gender, but not for objects. More interestingly, participants exhibited a selective inversion deficit when making similarity judgments between different facial expressions of emotion, but not for gender or objects. These results suggest a three-way dissociation between facial expression of emotion, gender, and object processing.

Face and object discrimination in autism, and relationship to IQ and age.

The current study tested fine discrimination of upright and inverted faces and objects in adolescents with Autism Spectrum Disorder (ASD) as compared to age- and IQ-matched controls. Discrimination sensitivity was tested using morphed faces and morphed objects, and all stimuli were equated in low-level visual characteristics (luminance, contrast, spatial frequency make-up). Participants with ASD exhibited slight, non-significant impairments in discrimination sensitivity for faces, yet significantly enhanced discrimination sensitivity for objects. The ASD group also showed a protracted development of face and object inversion effects. Finally, for ASD participants, face sensitivity improved with increasing IQ while object sensitivity improved with age. By contrast, for controls, face sensitivity improved with age, but neither face nor object sensitivity was influenced by IQ. These findings suggest that individuals with ASD follow a qualitatively different path in the development of face and object processing abilities.

Contrast negation differentiates visual pathways underlying dynamic and invariant facial processing.

Bruce and Young (1986) proposed a model for face processing that begins with structural encoding, followed by a split into two processing streams: one for the dynamic aspects of the face (e.g., facial expressions of emotion) and the other for the invariant aspects of the face (e.g., gender, identity). Yet how this is accomplished remains unclear. Here, we took a psychophysical approach using contrast negation to test the Bruce and Young model. Previous research suggests that contrast negation impairs processing of invariant features (e.g., gender) but not dynamic features (e.g., expression). In our first experiment, participants discriminated differences in gender and facial expressions of emotion in upright, inverted, and contrast-negated faces. Results revealed a profound impairment for contrast-negated gender discrimination, whereas expression discrimination remained relatively robust to contrast negation. To test whether this differential effect occurs during perceptual encoding, we conducted three additional experiments in which we measured aftereffects following upright, inverted, or contrast-negated face adaptation for the same discrimination task as in the first experiment. Results showed a mild impairment with contrast negation during perceptual encoding for both gender and expression, followed by a marked gender-specific deficit during contrast-negated face discrimination. Taken together, our results suggest that there are shared neural mechanisms during perceptual encoding, and at least partially separate neural mechanisms during recognition and decision making for dynamic and invariant facial-feature processing.

Development of face discrimination abilities, and relationship to magnocellular pathway development, between childhood and adulthood.

The current study tested the development of face and object processing in young children (mean age = 5.24 years), adolescents (mean age = 15.8 years), and adults (mean age = 21.1 years) using stimuli that were equated for low-level visual characteristics (luminance, contrast, and spatial frequency make-up) and methods that equate for difficulty across ages. We also tested sensitivity to luminance and chromatic contrast (i.e., thought to be mediated primarily by the subcortical Magnocellular (M) and Parvocellular (P) pathways, respectively) to determine whether age-related improvements in face or object discrimination were driven by age-related changes in the M and/or P pathways. Results showed a selective age-related improvement in face sensitivity and a relationship between age-related increases in face sensitivity and luminance contrast sensitivity. These results add to the mounting evidence that the M pathway may influence face processing.

Seeing faces as objects: no face inversion effect with geometrical discrimination.

Inversion dramatically impairs face perception, recognition, and discrimination. Yet it does not interfere with the ability to make precise estimates of facial feature distances. To investigate this discontinuity between facial feature distance estimation and general perception and recognition, we assessed the effect of inversion on the discrimination of differences in facial compression and elongation or expansion using geometrically distorted faces. The results clearly showed that geometrical face discrimination is not subject to the traditional face inversion effect and did not show a benefit for natural faces. Although discrimination thresholds were not affected by inversion, response times to the distance judgments were faster with inversion, especially when the inverted faces contained natural configurations. Based on these counterintuitive results, we suggest that participants used analytical processing to do the discrimination task. Moreover, we suggest that the depth with which a face is holistically encoded depends on the nature of the task, face orientation, and similarity between a face and the prototypical face template.

New "golden" ratios for facial beauty.

In four experiments, we tested the existence of an ideal facial feature arrangement that could optimize the attractiveness of any face given its facial features. Participants made paired comparisons of attractiveness between faces with identical facial features but different eye-mouth distances and different interocular distances. We found that although different faces have varying attractiveness, individual attractiveness is optimized when the face's vertical distance between the eyes and the mouth is approximately 36% of its length, and the horizontal distance between the eyes is approximately 46% of the face's width. These "new" golden ratios match those of an average face.