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.     

Emotion regulates attention: The relation between facial configurations,facial emotion,and visual attention

We used threatening, friendly, and neutral schematic facial stimuli, in which three, two, or one feature(s) conveyed emotion, to test the hypothesis that humans preferentially orient attention towards threat, and to examine the relation between facial features, emotional impression, and visual attention. Using a visual search paradigm, participants searched for discrepant faces in arrays of otherwise identical faces. Subsequently they also rated their emotional impression of the involved stimuli. Across four experiments, we found faster and more accurate detection of threatening than friendly faces, even when only one feature conveyed the emotion. Facial features affected both attention and emotion in the rank order eyebrows > mouth > eyes. Finally, the emotional impression of a face predicted its effect on attention.     

The eyebrow frown: a salient social signal

Seven experiments investigated the finding that threatening schematic faces are detected more quickly than nonthreatening faces. Threatening faces with v-shaped eyebrows (angry and scheming expressions) were detected more quickly than nonthreatening faces with inverted v-shaped eyebrows (happy and sad expressions). In contrast to the hypothesis that these effects were due to perceptual features unrelated to the face, no advantage was found for v-shaped eyebrows presented in a nonfacelike object. Furthermore, the addition of internal facial features (the eyes, or the nose and mouth) was necessary to produce the detection advantage for faces with v-shaped eyebrows. Overall, the results are interpreted as showing that the v-shaped eyebrow configuration affords easy detection, but only when other internal facial features are present.     

The role of eyebrows in face recognition

A fundamental challenge in face recognition lies in determining which facial characteristics are important in the identification of faces. Several studies have indicated the significance of certain facial features in this regard, particularly internal ones such as the eyes and mouth. Surprisingly, however, one rather prominent facial feature has received little attention in this domain: the eyebrows. Past work has examined the role of eyebrows in emotional expression and nonverbal communication, as well as in facial aesthetics and sexual dimorphism. However, it has not been made clear whether the eyebrows play an important role in the identification of faces. Here, we report experimental results which suggest that for face recognition the eyebrows may be at least as influential as the eyes. Specifically, we find that the absence of eyebrows in familiar faces leads to a very large and significant disruption in recognition performance. In fact, a significantly greater decrement in face recognition is observed in the absence of eyebrows than in the absence of eyes. These results may have important implications for our understanding of the mechanisms of face recognition in humans as well as for the development of artificial face-recognition systems.     

Reaction time measures of feature saliency in schematic faces

Two separate paradigms utilizing measurements of reaction time were employed to study facial feature saliency in schematic line drawn faces. In the first paradigm the speed of response to the omission of different facial components was measured, and in the second, the speed of response to feature substitution was measured. In both paradigms the facial features were presented in a random temporal sequence in order to minimise preferential scanning strategies. The two separate paradigms reflected the feature hierarchy most commonly found in the literature, ie the outline and eyes are more salient than the nose and mouth in terms of both speed of processing and error rate. In a third study the feature substitution paradigm was used to investigate the effects of feature saliency on the perception of emotional faces. The results suggest a change in the eyes/mouth hierarchy so that the mouth becomes the most salient feature in the surprised, happy, and sad target faces. This reverse in hierarchy, however, was not evident with the angry target face. These results are discussed in terms of changes in the focus of 'attention' and/or changes in 'processing efficiency'.     

The meaningfulness and meaning of schematic faces

A pool of 128 schematic faces was generated by varying brow, mouth, nose, eye height, and eye shape. Ratings of meaningfulness (how easy it was to find an adjective describing the face) and meaning (the adjective given to the face) were mainly a function of brow and mouth. When brow and mouth were horizontal, faces were least meaningful and neutral in expression; if either brow or mouth moved from the horizontal, faces increased in meaningfulness, meaning being dependent on the moving feature; when both brow and mouth moved from the horizontal, faces were most meaningful, and their expression was a function of the combination of brow and mouth.     

Visual search for schematic emotional faces: Angry faces are more than crosses

Recent studies of the face in the crowd effect, the faster detection of angry than of happy faces in visual search, suggest that for schematic faces it reflects on perceptual features like inward pointing lines rather than on emotional expressions. Removing a potential confound, Experiments 1–2 replicate the preferential detection of stimuli with inward pointing lines, but Experiment 2a indicates that a surrounding circle is required for the effect to emerge. Experiments 3–7 failed to find evidence for faster detection of schematic faces comprising only the elements critical for the faster detection of angry faces according to a low level visual feature account, inward tilted brows and upturned mouth. Faster detection of anger was evident if eyes or eyes and noses were added, but only if their placement was consistent with the first order relations among these elements in a human face. Drawing the critical elements in thicker, higher contrast lines also led to an anger advantage, but this was smaller than that seen for the complete faces. The present results suggest that, while able to support faster target detection, a prevalence of inward pointing lines is not sufficient to explain the detection advantage of angry schematic faces.     

Detecting emotional faces and features in a visual search paradigm: are faces special?

In 2 experiments, participants were presented schematic faces with emotional expressions (threatening, friendly) in a neutral-faces context or neutral expressions in an emotional-faces context. These conditions were compared with detection performance in displays containing key features of emotional faces not forming the perceptual gestalt of a face. Supporting the notion of a threat detection advantage, Experiment 1 found that threatening faces were faster detected than friendly faces, whereas no difference emerged between the corresponding feature conditions. Experiment 2 increased task difficulty with a backward masking procedure and found corresponding results. In neither of the studies was the threat detection advantage associated with reduced accuracy. However, features were, in general, detected faster than faces when task difficulty was high.     

Visual search for schematic emotional faces risks perceptual confound

Several studies have used a visual search task to demonstrate that schematic negative-face targets are found faster and/or more efficiently than positive ones, with these findings taken as evidence that negative emotional expression is capable of guiding attentional allocation in visual search. A common hypothesis is that these effects should be disrupted by face inversion; however, this has not been consistently demonstrated, and raises the possibility of a perceptual confound. One candidate confound is the feature of "closure" (see Wolfe & Horowitz, 2004) caused by the down-turned mouth adjacent to edge of the face. This was investigated in the present series of experiments. In Experiment 1, the speed advantage for upright negative faces was replicated. In Experiment 2, the effect was not disrupted with inversion, and an efficiency advantage emerged, suggesting that perceptual features could be causing the advantage. In Experiment 3, speed and efficiency effects were seen when this perceptual characteristic remained but face features were scrambled. Taken together, these findings suggest that visual search using schematic faces containing a curved-line mouth feature cannot provide a valid test of guided search by negative facial emotion unless this confound is controlled.     

Positive facial expressions are recognized faster than negative facial expressions, but why?

Three experiments examined the recognition speed advantage for happy faces. The results replicated earlier findings by showing that positive (happy) facial expressions were recognized faster than negative (disgusted or sad) facial expressions (Experiments 1 and 2). In addition, the results showed that this effect was evident even when low-level physical differences between positive and negative faces were controlled by using schematic faces (Experiment 2), and that the effect was not attributable to an artifact arising from facilitated recognition of a single feature in the happy faces (up-turned mouth line, Experiment 3). Together, these results suggest that the happy face advantage may reflect a higher-level asymmetry in the recognition and categorization of emotionally positive and negative signals.     

Does matching of internal and external facial features depend on orientation and viewpoint?

Although it is recognized that external (hair, head and face outline, ears) and internal (eyes, eyebrows, nose, mouth) features contribute differently to face recognition it is unclear whether both feature classes predominately stimulate different sensory pathways. We employed a sequential speed-matching task to study face perception with internal and external features in the context of intact faces, and at two levels of contextual congruency. Both internal and external features were matched faster and more accurately in the context of totally congruent/incongruent facial stimuli compared to just featurally congruent/incongruent faces. Matching of totally congruent/incongruent faces was not affected by the matching criteria, but was strongly modulated by orientation and viewpoint. On the contrary, matching of just featurally congruent/incongruent faces was found to depend on the feature class to be attended, with strong effects of orientation and viewpoint only for matching of internal features, but not of external features. The data support the notion that different processing mechanisms are involved for both feature types, with internal features being handled by configuration sensitive mechanisms whereas featural processing modes dominate when external features are the focus.     

Looking at faces: first-order and second-order features as determinants of facial appearance

The encoding and relative importance of first-order (discrete) and second-order (configural) features in mental representations of unfamiliar faces have been investigated. Nonmetric multidimensional scaling (KYST) was carried out on similarity judgments of forty-one photographs of faces (homogeneous with respect to sex, race, facial expression, and, to a lesser extent, age). A large set of ratings, measurements, and ratios of measurements of the faces was regressed against the three-dimensional KYST solution in order to determine the first-order and second-order features used to judge similarity. Parameters characterizing both first-order and second-order features emerged as important determinants of facial similarity. First-order feature parameters characterizing the appearance of the eyes, eyebrows, and mouth, and second-order feature parameters characterizing the position of the eyes, spatial relations between the internal features, and chin shape correlated with the dimensions of the KYST solution. There was little difference in the extent to which first-order and second-order features were encoded. Two higher-level parameters, age and weight, were also used to judge similarity. The implications of these results for mental representations of faces are discussed.     

The effect of feature displacement on the perception of well-known faces

The effect of feature displacement within two well-known faces (Terry Wogan and Cyril Smith) was examined. Image processing equipment was used to produce stimuli in which the features of an original facial image were displaced to form a number of modified images. This technique was first reported by Haig, in a recognition study in which the effect of feature displacement within unfamiliar faces was investigated. In the present experiment a perceptual judgement task was carried out in which subjects were presented with a number of modified faces and asked to judge how dissimilar these were with respect to an original image. A multi-dimensional scaling analysis of the comparative judgements of the subjects revealed a two-dimensional solution involving displacement of the eyes and mouth. A clear division between up/down and inward/outward displacement within these features (particularly the eyes) was observed. A similar pattern of results was found for both well-known faces. This result indicates that subjects were responding to changes in the facial configuration produced by the different types of feature displacement (horizontal or vertical), as opposed to movement of the features per se. Finally, the results also indicate that the displacement of inner features (mouth, eyes, nose) was more noticeable than displacement of the outer facial features (eg hairline).     

The ups and downs of face perception: evidence for holistic encoding of upright and inverted faces

A visual-search task was used to investigate the influence of facial organisation on discrimination of an internal facial feature. Participants searched for a downturned mouth in arrays of one to six faces that differed only in the target feature, with distractor faces containing an upturned mouth. Feature search was tested in four different face contexts: upright unaltered faces, inverted unaltered faces, upright faces in which the internal features were scrambled, or inverted scrambled faces. Normal face organisation facilitated feature search in upright faces, but slowed it in inverted faces. These findings demonstrate an interdependence of features and their configuration in the perceptual analysis of both upright and inverted faces.     

Preattentive analysis of facial expressions of emotion

Abstract

Some experiments have shown that a face having an expression different from the others in a crowd can be detected in a time that is independent of crowd size. Although this pop-out effect suggests that the valence of a face is available preattentively, it is possible that it is only the detection of sign features (e.g. angle of brow) which triggers an internal code for valence. In experiments testing the merits of valence and feature explanations, subjects searched displays of schematic faces having sad, happy, and vacant mouth expressions for a face having a discrepant sad or happy expression. Because inversion destroys holistic face processing and the implicit representation of valence, a critical test was whether pop-out occurred for inverted faces. Flat search functions (pop-out) for upright and inverted faces provided equivocal support for both explanations. But intercept effects found only with normal faces indicated valences had been analysed at an early stage of stimulus encoding.     

Deployment of attention to the configuration of features in facelike patterns by ten-week-old infants

Abstract

Three experiments were conducted to investigate the response of 10-week-old infants to the configuration of features in facelike patterns. In each experiment a series of preview trials was shown before. facelike patterns were presented on test trials. Preview stimuli were schematic drawings with non-facial configurations (Experiment 1), schematic drawings with facial configurations (Experiment 2), or photographs of men's and women's faces (Experiment 3). Test stimuli in all three experiments were facelike drawings that differed in the number and the configuration of their stimulus features.     

Still another confounded face in the crowd

Experiments using schematic faces developed by Öhman (Öhman, Lundqvist, &; Esteves, 2001) seem to document an anger-superiority effect, although we have come to question these experiments. Our work shows that the low-level features of these schematic faces interact with the face’s surround to produce effects that have been attributed to facial affect. Using relatively neutral faces that preserved the feature and surround spatial relationships of angry and happy schematic faces, we produced reaction times (RTs) that were indistinguishable from those found with angry and happy faces. We also found that the target face’s position within the crowd determined the magnitude of the advantage for angry faces as well as for relatively affect-neutral faces. Removing the facial surround reduces the advantage for angry faces, largely by improving performance on happy faces. There was an apparent small advantage for angry features without a surround. öhman faces avoid the problems associated with modified grayscale faces only to introduce an equally troubling confound.     

Features and their configuration in face recognition

Tanaka and Farah (1993) have proposed a holistic approach to face recognition in which information about the features of a face and their configuration are combined together in the face representation. An implication of the holistic hypothesis is that alterations in facial configuration should interfere with retrieval of features. In four experiments, the effect of configuration on feature recognition was investigated by creating two configurations of a face, one with eyes close together and one with eyes far apart. After subjects studied faces presented in one of the two configurations (eyes-close or eyes-far), they were tested for their recognition of features shown in isolation, in a new face configuration, and in the old face configuration. It was found that subjects recognized features best when presented in the old configuration, next best in the new configuration, and poorest in isolation. Moreover, subjects were not sensitive to configural information in inverted faces (Experiment 2) or nonface stimuli (i.e., houses; Experiments 3 and 4). Importantly, for normal faces, altering the spatial location of the eyes not only impaired subjects’ recognition of the eye features but also impaired their recognition of the nose and mouth features—features whose spatial locations were not directly altered. These findings emphasize the interdependency of featural and configural information in a holistic face representation.     

Not just another face in the crowd: Detecting emotional schematic faces during continuous flash suppression

To test whether threatening visual information receives prioritized processing, many studies have examined visual search for emotional schematic faces. Still, it has remained unclear whether negative or positive schematic faces are processed more efficiently. We used continuous flash suppression, a variant of binocular rivalry, to render single emotional schematic faces invisible and measured whether negative or positive faces have an advantage in accessing awareness. Across three experiments, positive faces were detected more quickly than negative faces. A fourth experiment indicated that this positive face advantage was unrelated to the valence of the face stimuli but due to the relative orientation of the mouth curvature and the face contour. These findings demonstrate the impact of configural stimulus properties on perceptual suppression during binocular rivalry and point to a perceptual confound present in emotional schematic faces that might account for some ambiguous results obtained with schematic face stimuli in previous studies. (PsycINFO Database Record (c) 2012 APA, all rights reserved).