Chimeric Faces Research Articles

A Web-based study of cerebral asymmetry for perception of emotion

Many studies have examined cerebral asymmetry via lateralized presentation of stimuli using specialized software. Because these studies typically require extensive control over variables such as stimulus exposure duration, size, location, and so forth, they are not easily transferred to the World Wide Web. The present study replicated a free-vision, chimeric faces task via the Internet, using HTML and JavaScript. Previous results had shown that right-handed participants tend to perceive a chimeric face with a smile to their (the viewers') left as happier than its mirror image. That result was replicated in the Web-based study, and the leftward bias was actually significantly greater than that found using the traditional pencil-and-paper version of the task. Possible reasons for this difference are discussed.

Hemispheric metacontrol and cerebral dominance in healthy individuals investigated by means of chimeric faces

Cerebral dominance and hemispheric metacontrol were investigated by testing the ability of healthy participants to match chimeric, entire, or half faces presented tachistoscopically. The two hemi-faces compounding chimeric or entire stimuli were presented simultaneously or asynchronously at different exposure times. Participants did not consciously detect chimeric faces for simultaneous presentations lasting up to 40 ms. Interestingly, a 20 ms separation between each half-chimera was sufficient to induce detection of conflicts at a conscious level. Although the presence of chimeric faces was not consciously perceived, performance on chimeric faces was poorer than on entire- and half-faces stimuli, thus indicating an implicit processing of perceptual conflicts. Moreover, the precedence of hemispheric stimulation over-ruled the right hemisphere dominance for face processing, insofar as the hemisphere stimulated last appeared to influence the response. This dynamic reversal of cerebral dominance, however, was not caused by a shift in hemispheric specialization, since the level of performance always reflected the right hemisphere specialization for face recognition. Thus, the dissociation between hemispheric dominance and specialization found in the present study hints at the existence of hemispheric metacontrol in healthy individuals.

Laterality Biases to Chimeric Faces in Asperger Syndrome: What is Right About Face-Processing?

People show a left visual field (LVF) bias for faces, i.e., involving the right hemisphere of the brain. Lesion and neuroimaging studies confirm the importance of the right-hemisphere and suggest separable neural pathways for processing facial identity vs. emotions. We investigated the hemispheric processing of faces in adults with and without Asperger syndrome (AS) using facial emotion and identity chimeric tasks. Controls showed an LVF bias in both tasks, but no perceptual bias in a non-social control task. The AS group showed an LVF bias during both tasks, however the bias was reduced in the identity condition. Further, the AS group showed an LVF bias in the non-social condition. These results show a differential pattern of hemispheric processing of faces in AS.

Are perceptual judgments dissociated from motor processes?—A prism adaptation study

When asked to choose which of two chimeric faces composed of ‘smiling’ and ‘neutral’ half-faces is happier, healthy adults select the face in which the left half is smiling. Here, we show that this perceptual leftward bias is associated with a bias in eye movements to the same side. However, when we shifted the pattern of eye movements towards the right side by using prismatic lenses, we did not observe a concurrent shift in the perceptual judgments. Therefore, we argue that overt motor responses are not necessary for perceptual judgments. Furthermore, we argue that while prism adaptation influences performance on motor tasks, it cannot influence higher-order representational processes.

Asymmetric bias in perception of facial affect among Roman and Arabic script readers

The asymmetric chimeric faces test is used frequently as an indicator of right hemisphere involvement in the perception of facial affect, as the test is considered free of linguistic elements. Much of the original research with the asymmetric chimeric faces test was conducted with subjects reading left-to-right Roman script, i.e., English. As readers of right-to-left scripts, such as Arabic, demonstrated a mixed or weak rightward bias in judgements of facial affect, the influence of habitual scanning direction was thought to intersect with laterality. We administered the asymmetric chimeric faces test to 1239 adults who represented a range of script experience, i.e., Roman script readers (English and French), Arabic readers, bidirectional readers of Roman and Arabic scripts, and illiterates. Our findings supported the hypothesis that the bias in facial affect judgement is rooted in laterality, but can be influenced by script direction. Specifically, right-handed readers of Roman script demonstrated the greatest mean leftward score, and mixed-handed Arabic script readers demonstrated the greatest mean rightward score. Biliterates showed a gradual shift in asymmetric perception, as their scores fell between those of Roman and Arabic script readers, basically distributed in the order expected by their handedness and most often used script. Illiterates, whose only directional influence was laterality, showed a slight leftward bias.

Lateralised processing of positive facial emotion: sex differences in strength of hemispheric dominance

Sex differences in lateralisation have been examined frequently, but have found varying and contradictory results. The experiment presented in this paper examines the lateralisation of processing positive facial emotion in 276 right handed undergraduates (138 males, 138 females). All participants completed two behavioural tests of lateralisation: a handedness preference questionnaire and a chimeric faces emotion judgement task, which measured strength of lateralisation for the perception of positive facial emotion. A highly significant difference was found for the chimeric faces task only: males were more strongly lateralised than females, although both males and females tended to be right hemisphere dominant. The results suggest that females are more bilaterally distributed and hence have greater access to mechanisms located in each hemisphere.

Are the perceptual biases found in chimeric face processing reflected in eye-movement patterns?

Studies of patients with focal brain lesions and neuroimaging indicate that face processing is predominantly based on right hemisphere function. Additionally, experiments using chimeric faces, where the left and the right-hand side of the face are different, have shown that observers tend to bias their responses toward the information on the left. Here, we monitored eye-movements during a gender identification task using blended face images for both whole and chimeric (half female, half male) faces [Neuropsychologia 35 (1997) 685]. As expected, we found a left perceptual bias: subjects based their gender decision significantly more frequently on the left side of the chimeric faces. Analysis of the first saccade showed a significantly greater number of left fixations independent of perceptual bias presumably reflecting the tendency to first inspect the side of the face better suited to face analysis (left side of face/right hemisphere). On top of this though, there was a relationship between response and fixation pattern. On trials where participants showed a left perceptual bias they produced significantly more left saccades and fixated for longer on the left. In contrast, for trials where participants showed a right perceptual bias there was no reliable difference between the number, or total fixation duration, on the left or the right. These results demonstrate that on a trial-by-trial basis subtle differences in the extent of left or right side scanning are related to the perceptual response of the participant, although an overall initial fixation bias to the left occurs irrespective of response bias.

My left brain and me: a dissociation in the perception of self and others

We investigated hemispheric asymmetries in face processing using a task in which participants judged the likeness of chimeric faces to their own face and to the face of a close friend based on their memory for those faces. When asked to choose which of two mirror-symmetric images (one made from the left half and one from the right half of a photograph of their face) looked more like themselves as remembered, participants showed a significant bias for the composite corresponding to the half face that lies in their right visual field when they look at themselves in the mirror. They showed the opposite bias when asked to make the same choice for images of a close friend, that is, they showed a significant bias for the composite corresponding to the half face that lies in their left visual field when they look at their friend. This result shows that in the case of these highly familiar faces—self and friend—the perceptual asymmetry is preserved in the memory representation. Assuming that people remember their own face as a mirror-image, the data also suggest a dissociation in face processing such that the left brain is dominant for the recognition of self and the right brain is dominant for the recognition of others.

Perceptual asymmetries in normal children and children with attention deficit/hyperactivity disorder

Perceptual asymmetries in normal right-handed children (7–12 years of age) and children with attention deficit/hyperactivity disorder (ADHD), combined type, were investigated using various chimeric stimuli in free-viewing conditions. In the face-matching task, participants indicated which of two symmetrical face chimeras more closely resembled the original; in the chimeric faces task, participants indicated which of a pair of faces appeared happier; and in the grey scales task participants indicated which of two shaded rectangles appeared to be darker overall. Leftward biases were found for normal children with no effects of age. Contrary to expectations, normal leftward biases were also found for ADHD children in the face-matching and the chimeric faces tasks; however, a significant leftward bias was not observed in the grey scales task. The absence of anomalous perceptual bias in ADHD children on these purely perceptual tasks, suggests that anomalous perceptual asymmetries observed in other tasks (line bisection and cancellation tasks) may have been confounded by the motor response, and/or the explicit spatial components of those tasks.

Emotion Processing in Chimeric Faces: Hemispheric Asymmetries in Expression and Recognition of Emotions

Since the discovery of facial asymmetries in emotional expressions of humans and other primates, hypotheses have related the greater left-hemiface intensity to right-hemispheric dominance in emotion processing. However, the difficulty of creating true frontal views of facial expressions in two-dimensional photographs has confounded efforts to better understand the phenomenon. We have recently described a method for obtaining three-dimensional photographs of posed and evoked emotional expressions and used these stimuli to investigate both intensity of expression and accuracy of recognizing emotion in chimeric faces constructed from only left- or right-side composites. The participant population included 38 (19 male, 19 female) African-American, Caucasian, and Asian adults. They were presented with chimeric composites generated from faces of eight actors and eight actresses showing four emotions: happiness, sadness, anger, and fear, each in posed and evoked conditions. We replicated the finding that emotions are expressed more intensely in the left hemiface for all emotions and conditions, with the exception of evoked anger, which was expressed more intensely in the right hemiface. In contrast, the results indicated that emotional expressions are recognized more efficiently in the right hemiface, indicating that the right hemiface expresses emotions more accurately. The double dissociation between the laterality of expression intensity and that of recognition efficiency supports the notion that the two kinds of processes may have distinct neural substrates. Evoked anger is uniquely expressed more intensely and accurately on the side of the face that projects to the viewer's right hemisphere, dominant in emotion recognition.

Relationship between coping styles and perceptual asymmetry.

This study examined the relationship between coping styles and hemispheric asymmetry, on the basis of prior evidence of reduced posterior right hemisphere (RH) activity in depression, and the relationship between ruminative coping and depression. Two samples of undergraduates (N = 170) completed chimeric faces tasks and 2 measures of coping styles, the self-report Responses Styles Questionnaire and a behavioral choice task. In women but not in men, self-reported rumination was associated with a decreased RH bias on the emotion-based chimeric task. In both genders, choosing to engage in an emotional task was associated with increased RH involvement. Results indicate that although brooding and dwelling on the negative may be associated with decreased RH involvement, openness to emotion may be associated with increased RH involvement.

Inner and outer face perception in children with autism.

Possible peculiarities in face perception in the autistic population were explored through two experiments. Fourteen autistic children (mean age=10 years 1 month) were individually matched to verbal mental age (VMA) and chronological age (CA) subjects. In a first experiment, subjects were to match faces on the basis of either their outer (hair, chin, ears) or their inner (eyes, nose, mouth) aspects. Autistic children performed equally well in both conditions, while VMA-matched children performed better in the outer than the inner part condition. In a second experiment, chimeric faces consisting of the outer part of an individual's face and the inner part of another individual's face were presented to the subjects. None of the groups showed a preference for neither the outer nor the inner part of the face in this condition. Results were discussed in terms of the existence of a local visual processing strategy in this population.

HIGHLIGHTS IN THIS ISSUE

The editorial in this issue reviews the orexins/hypocretins, a recently recognized group of neuropeptides, involved in sleep, arousal, narcolepsy and possibly other disorders.Two articles concern epidemiology. Kessler and colleagues (pp. 959–976) report large scale development and validation of 10-item and 6-item versions of a scale with impressive performance in screening for DSM-IV psychiatric disorder in US and Australian general populations. Sacker & Wiggins (pp. 977–990) use two longitudinal cohort studies to examine gender and social class differences in psychological distress. Both narrowed over two decades with the higher rates in women and those in manual occupations falling, to become nearer males and non-manual occupations. Disadvantage is apparently lessening.In another study of gender and disorder Fergusson and colleagues in New Zealand (pp. 991–996) find that the greater exposure of females to sexual violence explains some, but not all of their greater liability to internalizing disorders. In other aetiological studies, Enns et al. (pp. 997–1008) find associations of community disorder with lack of care on the Parental Bonding Instrument, while Reichborn-Kjennerud et al. (pp. 1009–1020) in a Norwegian twin sample find genetic links between back-neck pain and anxiety and depressive symptoms.Four studies concern depression. In an important neuroendocrine study of chronic depression Watson et al. (pp. 1021–1028) find absence of the usual depressive HPA axis abnormalities, strongly suggesting that these normalize with time. Matsuo et al. (pp. 1029–1038) employ the little-used non-invasive technique of near infrared spectroscopy, to show a reduction in euthymic affective disorder patients compared with controls in the increase of oxyHb in the frontal region during a verbal fluency task and during hyperventilation, indicating persisting or antecedent abnormalities. In a controlled trial Chabrol et al. (pp. 1039–1047) find a brief cognitive-behavioural intervention reduces depression scores in postpartum mothers at risk for post-natal depression. Fava et al. (pp. 1049–1057) find personality disorder diagnoses to decline in frequency after treatment for depression, suggesting that depression contributes to and antidepressant ameliorates the behaviours and attitudes which comprise the personality disorders.Two studies interface with psychoimmunology. In an important prospective study over up to 9 years, Leserman et al. (pp. 1059–1073) find progression of HIV accelerated by stressful life events, dysphoric mood and raised cortisol. Arnold et al. (pp. 1075–1089) report effects of inducing influenza-like symptoms in patients with chronic fatigue syndrome compared with normal controls. While somatic symptoms of CFS were exacerbated, cognitive and mood symptoms were not.Three papers report findings in schizophrenia. Hooley & Campbell (pp. 1091–1099) find high expressed emotion relatives attribute more control to ill family members than do low EE relatives, but are actually themselves more controlling. Their high control predicts relapse in schizophrenia but not depression. Gooding & Tallent (pp. 1101–1107) find that schizophrenics show atypical perceptual biases in response to emotional chimeric faces. Malla et al. (pp. 1109–1119) report predictors of outcome at 1 year of first-episode psychosis, including some potential modifiable factors such as medication adherence and residual symptoms.

Atypical depression: Enhanced right hemispheric dominance for perceiving emotional chimeric faces.

Atypical depression: Enhanced right hemispheric dominance for perceiving emotional chimeric faces.

Atypical depression: enhanced right hemispheric dominance for perceiving emotional chimeric faces.

Two studies compared hemispatial bias for perceiving chimeric faces in patients having either atypical or typical depression and healthy controls. A total of 245 patients having major depressive disorder (MDD) or dysthymia (164 with atypical features) and 115 controls were tested on the Chimeric Faces Test. Atypical depression differed from typical depression and controls in showing abnormally large right hemisphere bias. This was present in patients having either MDD or dysthymia and was not related to anxiety, physical anhedonia, or vegetative symptoms. In contrast, patients having MDD with melancholia showed essentially no right hemisphere bias. This is further evidence that atypical depression is a biologically distinct subtype and underscores the importance of this diagnostic distinction for neurophysiologic studies.

The left visual hemispace bias for the perception of chimeric faces: A further test of the difficulty of discrimination hypothesis

When people make judgments of visual-spatial forms, they generally perform better if the information is presented in their left visual hemispace (LVH), whereas for verbal material, they generally show a right visual hemispace (RVH) bias. For verbal material, the strength and direction of the effect also has been linked to task difficulty, with the bias shifting toward the RVH as task difficulty increases. Two experiments are presented that show the reverse direction of change for a nonverbal task; that is, when a nonverbal task is more difficult, the usual LVH effect shifts toward an RVH bias. Taking into account recent developments in theory and research on hemispheric differences in styles of information processing, we propose that task difficulty is related more generally to changes in processing style.

Left-side infant holding: A test of the hemispheric arousal -attentional hypothesis

When asked to hold a young infant in their arms, most adults hold on the left side (Harris, 1997). In a prior study, we found the same bias when we asked adults merely to imagine holding an infant in their arms (Harris, Almerigi, & Kirsch, 1999). It has been hypothesized that the left-side bias is the product of right-hemisphere arousal accompanying certain aspects of the act, causing attention to be driven to the contralateral, or left, side of personal space. Left-side holding, whether actual or imagined, thus would be consistent with the direction to which the holder's attention has been endogenously directed. We tested this hypothesis by giving 250 college students the "imagine-holding" task and then, as an independent measure of lateralized hemispheric arousal, a 34-item Chimeric Faces Test (CFT). On the "imagine" test, a significant majority reported a left-side hold, and, on the CFT, left-side holders had a significantly stronger left-hemispace bias than right-side holders, although both left- and right side holders had left-hemispace CFT biases. The results thus support the attentional-arousal hypothesis but indicate that other factors are contributing as well.

Patterns of hemispheric perceptual asymmetries: left hemispatial biases predict changes in anxiety and positive affect in undergraduate women.

Consistent with the tripartite model of anxiety and depression, hemispheric asymmetries may be differentially associated with depressive and anxious symptoms. Indeed, research has demonstrated that asymmetries do exist when examining hemispatial biases in both anxious and depressed individuals; however, the magnitude and direction of these asymmetries has been variable. The Chimeric Faces Task was used here to measure these asymmetries, along with measures for current and future levels of anxiety and depression. Results indicated that (a) increased left hemispatial biases at Time 1 predict increased anxiety (i.e., physiological hyperarousal) at Time 2 among female undergraduate students and (b) decreased left hemispatial biases at Time 1 predict decreased positive affectivity at Time 2 among the same participants. The possibility that hemispatial biases represent a vulnerability to future anxiety and depression is discussed.

Developmental Prosopagnosia: Should it be Taken at Face Value?

This study presents a rare case of developmental prosopagnosia. Structural magnetic resonance imaging (MRI) revealed no overt brain abnormalities. EP’s basic visual skills and visual memory were intact, as was his ability to judge age, sex and expression from faces, identify facial parts, and make face/non-face decisions. EP was impaired at recognizing famous and very familiar faces and describing visual images of famous faces. He also displayed an anterograde memory impairment for recently studied faces, and performed poorly on tests of unfamiliar face matching, most notably for chimeric faces. It is suggested that EP may be deficient at encoding configural representations of faces. EP appears to have a ‘pure’ (i.e. specific to faces) prosopagnosia, as he shows normal object recognition from unusual viewpoints, good gestalt completion for objects, but not for faces, normal visual imagery for objects but not for faces, a disruption of the inversion effect for faces but not for houses, and performs within the normal range on tests of within-category discriminations, even with unique exemplars of object categories such as famous buildings.

Perception of chimeric faces and the brain's pattern of asymmetry in schizophrenia

Perception of chimeric faces and the brain's pattern of asymmetry in schizophrenia