A role for eyebrows in regulating the visibility of eye gaze direction

The human eye is unique amongst those of primates in having white sclera against which the dark iris is clearly visible. This high-contrast structure makes the gaze direction of a human potentially easily perceptible to others. For a social creature such as a human, the ability to perceive the direction of another's gaze may be very useful, since gaze usually signals attention. We report data showing that the accuracy of gaze deviation detection is independent of viewing distance up to a certain critical distance, beyond which it collapses. This is, of itself, surprising since most visual tasks are performed better at closer viewing distances. Our data also show that the critical distance, but not accuracy, is affected by the position of the eyebrows so that lowering the eyebrows reduces the critical distance. These findings show that mechanisms exist by which humans could expand or restrict the availability of their gaze direction to others. A way to regulate the availability of the gaze direction signal could be an advantage. We show that an interpretation of eyebrow function in these terms provides a novel explanation for several well-known eyebrow actions, including the eyebrow flash.     

The effect of gaze on gaze direction while looking at art

In highly controlled cuing experiments, conspecific gaze direction has powerful effects on an observer’s attention. We explored the generality of this effect by using paintings in which the gaze direction of a key character had been carefully manipulated. Our observers looked at these paintings in one of three instructional states (neutral, social, or spatial) while we monitored their eye movements. Overt orienting was much less influenced by the critical gaze direction than what the cuing literature might suggest: An analysis of the direction of saccades following the first fixation of the critical gaze showed that observers were weakly biased to orient in the direction of the gaze. Over longer periods of viewing, however, this effect disappeared for all but the social condition. This restriction of gaze as an attentional cue to a social context is consistent with the idea that the evolution of gaze direction detection is rooted in social communication. The picture stimuli from this experiment can be downloaded from the Psychonomic Society’s Archive of Norms, Stimuli, and Data, www.psychonomic.org/archive.     

Eye remember you two: gaze direction modulates face recognition in a developmental study

The effects of gaze direction on memory for faces were studied in children from three different age groups (6-7, 8-9, and 10-11 years old) using a computerized version of a task devised by Hood, Macrae, Cole-Davies and Dias (2003). Participants were presented with a sequence of faces in an encoding phase, and were then required to judge which faces they had previously encountered in a surprise two-alternative forced-choice recognition test. In one condition, stimulus eye gaze was either direct or deviated at the viewing phase, and eyes were closed at the test phase. In another condition, stimulus eyes were closed at the viewing phase, with either direct or deviated gaze at the test phase. Modulation of gaze direction affected hit rates, with participants demonstrating greater accuracy for direct gaze targets compared to deviated gaze targets in both conditions. Reaction times (RT) to correctly recognized stimuli were faster for direct gaze stimuli at the viewing phase, but not at the test phase. The age group of participants differentially affected these measures: there was a greater hit rate advantage for direct gaze stimuli in older children, although RTs were less affected by age. These findings suggest that while the facilitation of face recognition by gaze direction is robust across encoding and recognition stages, the efficiency of the process is affected by the stage at which gaze is modulated.     

12- and 18-month-old infants follow gaze to spaces behind barriers

Infants follow the gaze direction of others from the middle of the first year of life. In attempting to determine how infants understand the looking behavior of adults, a number of recent studies have blocked the adult's line of sight in some way (e.g. with a blindfold or with a barrier). In contrast, in the current studies an adult looked behind a barrier which blocked the child's line of sight. Using two different control conditions and several different barrier types, 12- and 18-month-old infants locomoted a short distance in order to gain the proper viewing angle to follow an experimenter's gaze to locations behind barriers. These results demonstrate that, contra Butterworth, even 12-month-old infants can follow gaze to locations outside of their current field of view. They also add to growing evidence that 12-month-olds have some understanding of the looking behaviors of others as an act of seeing.     

Stronger reactivity to social gaze in virtual reality compared to a classical laboratory environment

People show a robust tendency to gaze at other human beings when viewing images or videos, but were also found to relatively avoid gaze at others in several real-world situations. This discrepancy, along with theoretical considerations, spawned doubts about the appropriateness of classical laboratory-based experimental paradigms in social attention research. Several researchers instead suggested the use of immersive virtual scenarios in eliciting and measuring naturalistic attentional patterns, but the field, struggling with methodological challenges, still needs to establish the advantages of this approach. Here, we show using eye-tracking in a complex social scenario displayed in virtual reality that participants show enhanced attention towards the face of an avatar at near distance and demonstrate an increased reactivity towards her social gaze as compared to participants who viewed the same scene on a computer monitor. The present study suggests that reactive virtual agents observed in immersive virtual reality can elicit natural modes of information processing and can help to conduct ecologically more valid experiments while maintaining high experimental control.     

Gaze direction and the extraction of egocentric distance

The angular declination of a target with respect to eye level is known to be an important cue to egocentric distance when objects are viewed or can be assumed to be resting on the ground. When targets are fixated, angular declination and the direction of the gaze with respect to eye level have the same objective value. However, any situation that limits the time available to shift gaze could leave to-be-localized objects outside the fovea, and, in these cases, the objective values would differ. Nevertheless, angular declination and gaze declination are often conflated, and the role for retinal eccentricity in egocentric distance judgments is unknown. We report two experiments demonstrating that gaze declination is sufficient to support judgments of distance, even when extraretinal signals are all that are provided by the stimulus and task environment. Additional experiments showed no accuracy costs for extrafoveally viewed targets and no systematic impact of foveal or peripheral biases, although a drop in precision was observed for the most retinally eccentric targets. The results demonstrate the remarkable utility of target direction, relative to eye level, for judging distance (signaled by angular declination and/or gaze declination) and are consonant with the idea that detection of the target is sufficient to capitalize on the angular declination of floor-level targets (regardless of the direction of gaze).     

“Avoiding or approaching eyes”? Introversion/extraversion affects the gaze-cueing effect

We investigated whether the extra-/introversion personality dimension can influence processing of others’ eye gaze direction and emotional facial expression during a target detection task. On the basis of previous evidence showing that self-reported trait anxiety can affect gaze-cueing with emotional faces, we also verified whether trait anxiety can modulate the influence of intro-/extraversion on behavioral performance. Fearful, happy, angry or neutral faces, with either direct or averted gaze, were presented before the target appeared in spatial locations congruent or incongruent with stimuli’s eye gaze direction. Results showed a significant influence of intra-/extraversion dimension on gaze-cueing effect for angry, happy, and neutral faces with averted gaze. Introverts did not show the gaze congruency effect when viewing angry expressions, but did so with happy and neutral faces; extraverts showed the opposite pattern. Importantly, the influence of intro-/extraversion on gaze-cueing was not mediated by trait anxiety. These findings demonstrated that personality differences can shape processing of interactions between relevant social signals.     

Eye-tracking data quality as affected by ethnicity and experimental design

Lack of accuracy in eye-tracking data can be critical. If the point of gaze is not recorded accurately and reliably, the information obtained or action executed might be different from what the user intended. This study reports trackability, accuracy, and precision as indicators of eye-tracking data quality as measured at various head positions and light conditions for a sample of participants from three different ethnic groups. It was found that accuracy and precision for Asian participants was worse than that for African and Caucasian participants. No significant differences were found between the latter two ethnic groups. Operating distance had the largest effect on data quality, since it affected all indicators for all ethnic groups. Illumination had no significant effect on accuracy or precision, but the accuracy achieved by African and Caucasian participants was better when the stimulus was presented on a dark background. Large gaze angles proved to be detrimental for trackability for African participants, while accuracy and precision were also affected adversely by larger gaze angles for two of the ethnicities.     

The Face of Wrath: Critical Features for Conveying Facial Threat

We examined the role of different facial features (shape of eyebrows, eyes, mouth, nose, and the direction of gaze) in conveying the emotional impact of a threatening face. In two experiments, a total of 100 high school students rated their impression of two sets of schematic faces in terms of semantic differential scales (Activity, Negative Evaluation, and Potency). It was found that the different facial features could be ordered hierarchically, with eyebrows as the most important feature, followed by mouth and eyes. Eyebrows thus fundamentally categorised faces as threatening or nonthreatening. The different shapes of mouth and eyes provided subsequent categorisations of faces within these primary categories.     

Electrophysiological responses in mothers to their own and unfamiliar child's gaze information

An attachment bond between a mother and her child is one of the most intimate human relationships. It is important for a mother to be sensitive to her child's gaze direction because exchanging gaze information plays a vital role in their relationship. Furthermore, recent studies have revealed differential neural activation patterns in mothers when presented the faces of their own children or the unfamiliar child of other people. Based on these findings, in the present study, we investigated whether mothers show differential neural responses to gaze information of their own child compared to that of an unfamiliar child. To this end, event-related-potentials elicited by the faces of one's own or an unfamiliar child with straight or averted gaze directions were measured using an oddball-paradigm. The results showed that peak amplitudes of the N170 component were enlarged by viewing the straight gazes compared to the averted gazes of one's own child, but not of an unfamiliar child. When the gaze was directed straight, the P3 amplitude elicited by one's own child's face is smaller than that elicited by an unfamiliar child's face. P3s elicited in viewing one's own child's face with averted gaze and in viewing an unfamiliar child's face with straight gaze were positively correlated with state-anxiety. These results bolster the hypothesis that processing the gaze information of one's own child elicits differential neural activation compared to the gaze information of an other person's unfamiliar child at both perceptual and evaluative stages of face processing.     

The face of wrath: The role of features and configurations in conveying social threat

We examined the role of single features and feature configurations in the effect of schematic faces on rated threat. A total of 101 medical students rated their emotional impression of schematic facial stimuli using semantic differential scales (Activity, Negative Valence, and Potency). In different parts of the experiment, the ratings concerned single features, eyebrow‐mouth configurations, or complete faces. Although eyebrows emerged as the overall most important feature, the effect of features was modulated by configuration. Simple configurations of eyebrows and mouth appeared to convey threat and nonthreat in a way highly similar to that of complete faces. In most cases, the configurations of eyebrows and mouth could significantly predict the effect of the complete faces.     

Direct gaze,eye movements,and covert and overt social attention processes

The present study is a replication and extension of previous research examining the effects of others’ gaze direction and gaze shifts on both participants’ (N = 32) manual responses, as an indicator of covert processes, and their visual attention, as an indicator of overt processes, within an experimental response time (RT) paradigm, under both fixed- and free-viewing instructions. Participants viewed arrays of faces displaying direct or averted gaze, which shifted or held their gaze, concurrent with the presentation of a target letter that participants had to identify overlaid on one face, all while their gaze was recorded with an eye-tracking system. Participants’ RTs and eye movements both revealed faster responses when the target face displayed either direct or shifted gaze, and especially when its gaze had shifted from averted to direct, though these effects were modulated by the viewing instructions. Thus, the findings replicate and extend previous research by revealing that direct gaze and dynamic motion onset affect both covert and overt attention.     

The positive and negative of human expertise in gaze perception

Judging where others look is crucial for many social and cognitive functions. Past accounts of gaze perception emphasize geometrical cues from the seen eye. Human eyes have a unique morphology, with a large white surround (sclera) to the dark iris that may have evolved to enhance gaze processing. Here we show that the contrast polarity of seen eyes has a powerful influence on gaze perception. Adult observers are highly inaccurate in judging gaze direction for images of human eyes with negative contrast polarity (regardless of whether the surrounding face is positive or negative), even though negative images of eyes preserve the geometric properties of positives that are judged accurately. The detrimental effect of negative contrast polarity is much larger for gaze perception than for other directional judgements (e.g. judging which way a head is turned). These results suggest an 'expert' system for gaze perception, which always treats the darker region of a seen eye as the part that does the looking.     

Preferred gaze direction and the vergence system at rest]

In two experiments the effects of binocular vergence, head tilt, and prolonged gaze inclination on the preferred vertical gaze direction were studied. Concurrently, dark vergence was measured to test a hypothesis on the effect that binocular vergence has on the preferred vertical direction of gaze. The previously reported influence of observation distance on the preferred gaze inclination was replicated. When the head was tilted backward, the preferred gaze inclination was lower and the effect of observation distance was reduced; when the head was tilted forward, the preferred gaze inclination was higher and the effect of observation distance was increased. After prolonged upward or downward gaze inclination the preferred vertical gaze direction was shifted up or down, respectively, while the effect of observation distance remained constant. Overall the change of the preferred vertical direction of gaze upon binocular fixation of near stimuli was accompanied by a reduced discrepancy between convergence and the resting state of the vergence system; additional implications of the hypothesis on the relation between individual resting vergence and the effect of observation distance on the preferred inclination of gaze could not be substantiated.     

Face in profile view reduces perceived facial expression intensity: An eye-tracking study

Recent studies measuring the facial expressions of emotion have focused primarily on the perception of frontal face images. As we frequently encounter expressive faces from different viewing angles, having a mechanism which allows invariant expression perception would be advantageous to our social interactions. Although a couple of studies have indicated comparable expression categorization accuracy across viewpoints, it is unknown how perceived expression intensity and associated gaze behaviour change across viewing angles. Differences could arise because diagnostic cues from local facial features for decoding expressions could vary with viewpoints. Here we manipulated orientation of faces (frontal, mid-profile, and profile view) displaying six common facial expressions of emotion, and measured participants' expression categorization accuracy, perceived expression intensity and associated gaze patterns. In comparison with frontal faces, profile faces slightly reduced identification rates for disgust and sad expressions, but significantly decreased perceived intensity for all tested expressions. Although quantitatively viewpoint had expression-specific influence on the proportion of fixations directed at local facial features, the qualitative gaze distribution within facial features (e.g., the eyes tended to attract the highest proportion of fixations, followed by the nose and then the mouth region) was independent of viewpoint and expression type. Our results suggest that the viewpoint-invariant facial expression processing is categorical perception, which could be linked to a viewpoint-invariant holistic gaze strategy for extracting expressive facial cues.     

Arrows don’t look at you: Qualitatively different attentional mechanisms triggered by gaze and arrows

Eye gaze conveys rich information concerning the states of mind of others, playing a critical role in social interactions, signaling internal states, and guiding others’ attention. On the basis of its social significance, some researchers have proposed that eye gaze may represent a unique attentional stimulus. However, contrary to this notion, the majority of the literature has shown indistinguishable attentional effects when eye gaze and arrows have been used as cues. Taking a different approach, in this study we aimed at finding qualitative attentional differences between gazes and arrows when they were used as targets instead of as cues. We used a spatial Stroop task, in which participants were required to identify the direction of eyes or arrows presented to the left or the right of a fixation point. The results showed that the two types of stimuli led to opposite spatial interference effects, with arrows producing faster reaction times when the stimulus direction was congruent with the stimulus position (a typical spatial Stroop effect), and eye gaze producing faster reaction times when it was incongruent (a “reversed” spatial Stroop effect). This reversed Stroop is interpreted as an eye-contact effect, therefore revealing the unique nature of eyes as special social-attention stimuli.     

Relational property between head and eye regions is the primary determinant of the efficiency in search for a deviant gaze

The human visual system is extremely sensitive to the directions of the gazes of others. However, the mechanism underlying gaze direction perception has yet to be clarified. The primary aim of the present study is to investigate whether the relational property between the local eye region and other facial regions serves as the primary visual system cue in detecting a direct gaze. Our results showed that search efficiency was determined primarily by the gaze direction indicated by the relational property regardless of the direction indicated by the local feature information of the eye region; this was true even when the gaze directions indicated by these two types of information were conflicting. These results bolster the hypothesis that the human visual system primarily accesses socially meaningful information in searching for a deviant gaze.     

Detecting and identifying offset gaze

A number of experiments have demonstrated that observers can accurately identify stimuli that they fail to detect (Rollman and Nachmias, 1972; Harris and Fahle, 1995; Allik et al. 1982, 2014). Using a 2x2AFC double judgements procedure, we demonstrated an analogous pattern of performance in making judgements about the direction of eye gaze. Participants were shown two faces in succession: one with direct gaze and one with gaze offset to the left or right. We found that they could identify the direction of gaze offset (left/right) better than they could detect which face contained the offset gaze. A simple Thurstonian model, under which the detection judgement is shown to be more computationally complex, was found to explain the empirical data. A further experiment incorporated metacognitive ratings into the double judgements procedure to measure observers’ metacognitive awareness (Meta-d’) across the two judgements and to assess whether observers were aware of the evidence for offset gaze when detection performance was at and below threshold. Results suggest that metacognitive awareness is tied to performance, with approximately equal Meta-d’ across the two judgements, when sensitivity is taken into account. These results show that both performance and metacognitive awareness rely not only on the strength of sensory evidence but also on the computational complexity of the decision, which determines the relative distance of that evidence from the decision axes.     

The look of love: gaze shifts and person perception

Gaze direction is a vital communicative channel through which people transmit information to each other. By signaling the locus of social attention, gaze cues convey information about the relative importance of objects, including other people, in the environment. For the most part, this information is communicated via patterns of gaze direction, with gaze shifts signaling changes in the objects of attention. Noting the relevance of gaze cues in social cognition, we speculated that gaze shifts may modulate people's evaluations of others. We investigated this possibility by asking participants to judge the likability (Experiment 1) and physical attractiveness (Experiment 2) of targets displaying gaze shifts indicative of attentional engagement or disengagement with the participants. As expected, person evaluation was moderated by the direction of gaze shifts, but only when the judgment under consideration was relevant to participants. We consider how and when gaze shifts may modulate person perception and its associated behavioral products.