Face-Specific Pupil Contagion in Infants

Pupil contagion is the phenomenon in which an observer’s pupil-diameter changes in response to another person’s pupil. Even chimpanzees and infants in early development stages show pupil contagion. This study investigated whether dynamic changes in pupil diameter would induce changes in infants’ pupil diameter. We also investigated pupil contagion in the context of different faces. We measured the pupil-diameter of 50 five- to six-month-old infants in response to changes in the pupil diameter (dilating/constricting) of upright and inverted faces. The results showed that (1) in the upright presentation condition, dilating the pupil diameter induced a change in the infants’ pupil diameter while constricting the pupil diameter did not induce a change, and (2) pupil contagion occurred only in the upright face presentation, and not in the inverted face presentation. These results indicate the face-inversion effect in infants’ pupil contagion.

Holistic face recognition is an emergent phenomenon of spatial processing in face-selective regions

Spatial processing by receptive fields is a core property of the visual system. However, it is unknown how spatial processing in high-level regions contributes to recognition behavior. As face inversion is thought to disrupt typical holistic processing of information in faces, we mapped population receptive fields (pRFs) with upright and inverted faces in the human visual system. Here we show that in face-selective regions, but not primary visual cortex, pRFs and overall visual field coverage are smaller and shifted downward in response to face inversion. From these measurements, we successfully predict the relative behavioral detriment of face inversion at different positions in the visual field. This correspondence between neural measurements and behavior demonstrates how spatial processing in face-selective regions may enable holistic perception. These results not only show that spatial processing in high-level visual regions is dynamically used towards recognition, but also suggest a powerful approach for bridging neural computations by receptive fields to behavior.

Attention to speaking mouth is reduced by face inversion in infants only from 9 months of age

Configural processing is a specialised perceptual mechanism that allows adult humans to quickly process facial information. It emerges before the first birthday and can be disrupted by upside-down presentation of the face (inversion). To date, little is known about the relationship of configural face processing to the emerging knowledge of audiovisual (AV) speech in infancy. Using eye-tracking we measured attention to speaking mouth in upright and inverted faces that were either congruent or incongruent with the speech sound. Face inversion affected looking at AV speech only in older infants (9- to 11- and 12- to 14-month-olds). The youngest group of infants (5- to 7-month-olds) did not show any differences in looking durations between upright and inverted faces, while in both older groups face inversion led to reduced looking at the articulating mouth. We also observed a stronger interest in the eyes in the youngest infants, followed by an increase in looking time to the mouth in both older groups. Our findings suggest that configural face processing is involved in AV speech processing already in infancy, indicating early integration of face and speech processing mechanisms in cognitive development.

Visual Similarity Versus Mental Rotation For Inverted and Upright Faces.

A major interest of research in face recognition lies in explaining the Face Inversion Effect (FIE), in which the recognition of an inverted face is less successful than that of an upright face. However, prior research has devoted little effort to examining how the cognitive system handles comparison between upright and inverted faces. In two experiments, such comparison is found to be based on visual similarity rather than on mental rotation of the inverted face to upright. Visual similarity is based on certain elements mutual to the two faces, which resist the transformation of inversion. These elements are symmetrical or salient components of the face, such as round eyes or thick lips.

Using transcranial Direct Current Stimulation (tDCS) to investigate why faces are and are not special

We believe we are now in a position to answer the question, "Are faces special?" inasmuch as this applies to the face inversion effect (better performance for upright vs inverted faces). Using a double-blind, between-subject design, in two experiments (n = 96) we applied a specific tDCS procedure targeting the Fp3 area while participants performed a matching-task with faces (Experiment 1a) or checkerboards from a familiar prototype-defined category (Experiment 1b). Anodal tDCS eliminated the checkerboard inversion effect reliably obtained in the sham group, but only reduced it for faces (although the reduction was significant). Thus, there is a component to the face inversion effect that we are not affecting with a tDCS procedure that can eliminate the checkerboard inversion effect. We suggest that the reduction reflects the loss of an expertise-based component in the face inversion effect, and the residual is due to a face-specific component of that effect.

Turning the Face Inversion Effect on Its Head: Violated Expectations of Orientation, Lighting, and Gravity Enhance N170 Amplitudes

Face inversion effects occur for both behavioral and electrophysiological responses when people view faces. In EEG, inverted faces are often reported to evoke an enhanced amplitude and delayed latency of the N170 ERP. This response has been attributed to the indexing of specialized face processing mechanisms within the brain. However, inspection of the literature revealed that, although N170 is consistently delayed to a variety of face representations, only photographed faces invoke enhanced N170 amplitudes upon inversion. This suggests that the increased N170 amplitudes to inverted faces may have other origins than the inversion of the face's structure. We hypothesize that the unique N170 amplitude response to inverted photographed faces stems from multiple expectation violations, over and above structural inversion. For instance, rotating an image of a face upside–down not only violates the expectation that faces appear upright but also lifelong priors about illumination and gravity. We recorded EEG while participants viewed face stimuli (upright vs. inverted), where the faces were illuminated from above versus below, and where the models were photographed upright versus hanging upside–down. The N170 amplitudes were found to be modulated by a complex interaction between orientation, lighting, and gravity factors, with the amplitudes largest when faces consistently violated all three expectations. These results confirm our hypothesis that face inversion effects on N170 amplitudes are driven by a violation of the viewer's expectations across several parameters that characterize faces, rather than a disruption in the configurational disposition of its features.

Holistic face recognition is an emergent phenomenon of spatial integration in face-selective regions

Spatial processing by receptive fields is a core property of the visual system. However, it is unknown how spatial coding in high-level regions contributes to recognition behavior. As face inversion is thought to disrupt typical ‘holistic’ processing of information in faces, we mapped population receptive fields (pRFs) with upright and inverted faces in the human visual system. In face-selective regions, but not primary visual cortex, pRFs and overall visual field coverage were smaller and shifted downward in response to face inversion. From these measurements, we successfully predicted the relative behavioral detriment of face inversion at different positions in the visual field. This correspondence between neural measurements and behavior demonstrates how spatial integration in face-selective regions enables holistic processing. These results not only show that spatial processing in high-level visual regions is dynamically used towards recognition, but also suggest a powerful approach for bridging neural computations by receptive fields to behavior.