Asymmetries in face processing: evidence for a right hemisphere perceptual advantage

The influence of single-session reward-based attentional bias modification on attentional biases towards threat as measured by the N2pc component

Attentional biases toward threatening faces have repeatedly been studied in the context of social anxiety, with etiological theories suggesting exacerbated biases as a possible cause for the latter. To counteract these postulated effects, research has focused on the concept of attentional bias manipulation (ABM), in which spatial contingencies between succeeding stimuli are traditionally employed in training paradigms designed to deliberately shift automatic attention processes away from threat-related stimuli. The ABM research field has been faced with various methodological challenges, such as inconsistent results, low reliabilities of dependent variables and a high susceptibility to moderating factors. We aimed to combine several recent approaches to address these issues. Drawing upon theories of value-driven attention, we explored reward-based contingencies in a Dot Probe task to improve the training's efficacy, combined with neurophysiological measures for greater reliability compared to reaction times, while evaluating the moderating effect of explicitness in the instruction. In a healthy sample (N = 60) and within a single session, we found a general attentional bias toward angry faces present across all conditions as indicated by the N2pc, which was, however, marked by large intrinsic lateralization effects, with submeasures exhibiting opposing polarities. This prompted us to explore an alternative, intrahemispheric calculation method. The new N2pc variant showed the attentional bias to have disappeared at the end of the training session within the explicit instruction group. Reliabilities of the main dependent variables were varied from excellent to questionable, which, together with the exploratory nature of the analysis, leaves this result as preliminary.

Flowers in the Attic: Lateralization of the detection of meaning in visual noise

The brain is a slave to sense; we see and hear things that are not there and engage in ongoing correction of these illusory experiences, commonly termed pareidolia. The current study investigates whether the predisposition to see meaning in noise is lateralized to one hemisphere or the other and how this predisposition to visual false-alarms is related to personality. Stimuli consisted of images of faces or flowers embedded in pink (1/f) noise generated through a novel process and presented in a divided-field paradigm. Right-handed undergraduates participated in a forced-choice signal-detection task where they determined whether a face or flower signal was present in a single-interval trial. Experiment 1 involved an equal ratio of signal-to-noise trials; experiment 2 provided more potential for illusionary perception with 25% signal and 75% noise trials. There was no asymmetry in the ability to discriminate signal from noise trials (measured using d') for either faces and flowers, although the response criterion (c) suggested a stronger predisposition to visual false alarms in the right visual field, and this was negatively correlated to the unusual experiences dimension of schizotypy. Counter to expectations, changing the signal-image to noise-image proportion in Experiment 2 did not change the number of false alarms for either faces and flowers, although a stronger bias was seen to the right visual field; sensitivity remained the same in both hemifields but there was a moderate positive correlation between cognitive disorganization and the bias (c) for "flower" judgements. Overall, these results were consistent with a rapid evidence-accumulation process of the kind described by a diffusion decision model mediating the task lateralized to the left-hemisphere.

Investigating attention in complex visual search

How we attend to and search for objects in the real world is influenced by a host of low-level and higher-level factors whose interactions are poorly understood. The vast majority of studies approach this issue by experimentally controlling one or two factors in isolation, often under conditions with limited ecological validity. We present a comprehensive regression framework, together with a matlab-implemented toolbox, which allows concurrent factors influencing saccade targeting to be more clearly distinguished. Based on the idea of gaze selection as a point process, the framework allows each putative factor to be modeled as a covariate in a generalized linear model, and its significance to be evaluated with model-based hypothesis testing. We apply this framework to visual search for faces as an example and demonstrate its power in detecting effects of eccentricity, inversion, task congruency, emotional expression, and serial fixation order on the targeting of gaze. Among other things, we find evidence for multiple goal-related and goal-independent processes that operate with distinct visuotopy and time course.

Recognition of facial expressions in individuals with elevated levels of depressive symptoms: an eye-movement study

Previous studies consistently reported abnormal recognition of facial expressions in depression. However, it is still not clear whether this abnormality is due to an enhanced or impaired ability to recognize facial expressions, and what underlying cognitive systems are involved. The present study aimed to examine how individuals with elevated levels of depressive symptoms differ from controls on facial expression recognition and to assess attention and information processing using eye tracking. Forty participants (18 with elevated depressive symptoms) were instructed to label facial expressions depicting one of seven emotions. Results showed that the high-depression group, in comparison with the low-depression group, recognized facial expressions faster and with comparable accuracy. Furthermore, the high-depression group demonstrated greater leftwards attention bias which has been argued to be an indicator of hyperactivation of right hemisphere during facial expression recognition.

Faces in the mist: illusory face and letter detection

We report three behavioral experiments on the spatial characteristics evoking illusory face and letter detection. False detections made to pure noise images were analyzed using a modified reverse correlation method in which hundreds of observers rated a modest number of noise images (480) during a single session. This method was originally developed for brain imaging research, and has been used in a number of fMRI publications, but this is the first report of the behavioral classification images. In Experiment 1 illusory face detection occurred in response to scattered dark patches throughout the images, with a bias to the left visual field. This occurred despite the use of a fixation cross and expectations that faces would be centered. In contrast, illusory letter detection (Experiment 2) occurred in response to centrally positioned dark patches. Experiment 3 included an oval in all displays to spatially constrain illusory face detection. With the addition of this oval the classification image revealed an eyes/nose/mouth pattern. These results suggest that face detection is triggered by a minimal face-like pattern even when these features are not centered in visual focus.

A serial test of the laterality of familiar face recognition

The purpose of the present study was to address the issue of laterality of familiar face recognition. Seventy-two participants judged familiar faces presented laterally or centrally for their "faceness," familiarity, occupation, and name (which represent four stages of familiar face processing) using one of three response modes-verbal, manual, or combined. The pattern of reaction times (RTs) implied a serial process of familiar face recognition. Centrally presented stimuli were recognized faster than laterally presented stimuli. No RT differences were found between the left and right visual fields (VFs) across all judgments and response modes. The findings were interpreted as supporting the notion that there are no significant hemispheric differences in familiar face recognition.

Menstrual cycle phase and mood effects on perceptual asymmetry

Several studies have reported shifts in perceptual asymmetry during the menstrual cycle, but the potential confounding effect of mood changes has been largely ignored. In this study, 24 female subjects completed four visual laterality tasks and a mood questionnaire at three phases of the cycle. Results indicate no overall effect of cycle phase on any of the asymmetry or mood scores. However, results revealed significant associations between affect and perceptual asymmetry on a face perception task. Implications for mood effects on perceptual asymmetry and future research on cycle-related shifts in asymmetry are discussed.

Visual field differences in an object decision task

Two experiments are reported which investigate hemispheric processing in an object decision task. Experiment 1 used 40 pictures of objects, and 40 pictures of nonobjects, and subjects decided manually whether each lateralized stimulus represented an object. Results indicated an interaction between visual field and response (yes versus no). There was a right visual field advantage for positive responses, but no difference between visual field for negative responses. Positive responses were faster than negative responses, and this effect was more marked for right visual field presentations. These results were replicated in a second experiment. The results are interpreted as reflecting a left hemisphere superiority at accessing stored structural descriptions of known objects. The possibility that left and right hemispheres use different methods of carrying out the task is also discussed.

A fifteen year follow-up of a case of developmental prosopagnosia

The term developmental prosopagnosia refers to an impairment in the recognition of familiar faces which has been present from birth in the absence of neurological disease or birth complications. The first reported study was by McConachie (1976, Cortex, 12: 76-82) and we report here a fifteen year follow-up on this case (AB). Recently developed theoretical models postulating separate processes involved in face perception and recognition were used to guide the exploration of her functional deficit. Our investigations with AB showed that basic visuo-sensory functions (acuity, contrast sensitivity, colour, etc.) were largely intact. General face perception (e.g. distinguishing between a face and a "nonface") was relatively well preserved. Recognition of familiar faces was severely impaired and she also showed problems with other face processing tasks (e.g. analysis of facial expression) and in object recognition. In object recognition she made errors based on visual similarity, and she had problems identifying exemplars from categories with many visually similar items. In addition, she was very poor at identifying objects or silhouettes from an unusual viewpoint. We conclude that AB has always been poor at constructing an effective internal representation sufficient to permit recognition of items which are visually difficult to discriminate. Therefore, she may not have been able to acquire useable stored representations either, because this deficit has been present since birth. This functional account was supported by subsequent studies which demonstrated a complete absence of covert face recognition.

Face processing and name retrieval in an anomic aphasic: names are stored separately from semantic information about familiar people

Recent models of face recognition have proposed that the names of familiar people are accessed from a lexical memory store that is distinct from the semantic memory store that holds information about such things as a familiar person's occupation and personality. Names are nevertheless retrieved via the semantic system. If such models are correct, then it should be possible for a patient to have full access to semantic information about familiar people while being unable to name many of them. We report this pattern in an anomic aphasic patient, EST, whose inability to recall the names of familiar people occurred in the context of a general word-finding problem. EST showed a preserved ability to access semantic information from familiar faces, voices, and spoken and written names and to process facial expressions, but he was unable to name many familiar faces. These findings are compatible with current models of face processing and challenge models which propose that names are stored alongside semantic information in a general-purpose long-term memory store.

Face processing, laterality and contrast sensitivity

Two separate reaction time studies concerning person recognition were conducted with ex-servicemen who incurred unilateral brain injury during the Second World War. The first experiment investigated the ability to construct a facial representation and involved deciding whether a stimulus represented a face or a "non-face" made by repositioning the facial features into an unnatural configuration. Men with posterior right hemisphere (RH) lesions performed this task more slowly than those with left hemisphere (LH) damage and control subjects; the latter two groups did not differ. The second experiment was designed to tap the most basic level of overt person recognition: awareness of familiarity. When faces were used as stimuli, the RH injured group again showed increased response latencies compared with the other two groups. The reverse pattern, slower reaction times for the men with LH lesions with no difference between RH injured and control subjects, emerged when written names were employed. Spatial contrast sensitivity functions were measured in both studies and although both LH and RH injured men showed impaired contrast sensitivity, no hemispheric difference was apparent. Instead, a double dissociation of impairments of contrast sensitivity and face processing was evident.

Right posterior brain-damaged patients are poor at assessing the age of a face

The ability to order unknown faces by age was investigated in right and left brain-damaged patients, divided into posterior and non-posterior groups on the basis of CT scan findings. A face recognition test and a figure ground discrimination test were also given. All three tests were affected by brain damage, but their sensitivity to the locus and side of lesion varied. While no hemispheric difference was found on the figure ground discrimination test, the face age test significantly discriminated patients with right posterior injury from any other brain-damaged group. The face recognition test occupied an intermediate position, with right posterior patients significantly impaired in comparison with right non-posterior patients and marginally impaired with respect to left posterior patients. Aphasia did not affect the performance of left brain-damaged patients on any of the tests. The findings are interpreted as evidence that damage of the right posterior hemisphere areas disrupts the structural encoding of visual information. Four prosopagnosic patients were also tested. Only those showing signs of apperceptive agnosia failed on the face age test.

Childhood prosopagnosia

K.D. has been unable to recognize people's faces since sustaining cerebral injury in infancy. Investigation of this disorder carried out when K.D. was aged 8 to 11 years showed that although her basic visual abilities were impaired, they were no poorer than those of other children who recognized faces without difficulty. K.D. had learned to read, but had not regained ability to recognize people's faces; instead she relied primarily on voices as a cue to person recognition. There was no evidence of any degree of overt or covert recognition of familiar faces, and K.D. also experienced problems in visual object recognition. She could, however, classify a visual input as a face, was able to perceive and imitate facial expressions, and was able to perform face matching tasks to an extent limited by her use of a feature by feature matching strategy. It is suggested that K.D.'s impairment affected higher order perceptual abilities, and is in a number of respects comparable to the impairments found in adult prosopagnosic patients.

Race categorization and face recognition stages in the processing of laterally displayed unknown faces

Bruyer and Dussart (1985) have recently shown that the "race effect", i.e. the difficulty in recognizing faces issuing from an ethnic group different from that of the subject, is limited to the right visual field. They suspected familiarization to be responsible for this asymmetry. In Exp. I, we tested this hypothesis by repeating the experiment of Bruyer and Dussart with a greater number of trials. A sample of 16 subjects were given the task of recognizing black and white faces laterally displayed for 180 msec. No laterality effect appeared, and the race effect was observed to an equal degree in each hemifield at all stages of the experimental session. It could thus be that various kinds of familiarization must be distinguished. In Exp. II, with 16 new subjects, the black and white faces were mixed so that the subjects had first to perform racial categorization, then a recognition. This time, an advantage of the left field appeared, the race effect was larger in the right than in the left field, and the race effect decreased with familiarization in the left field only. Two complementary experiments with 24 and 16 subjects showed that this phenomenon was not explainable by laterality effects in the early racial decision operation, but well by a lateralized effect of tasks requirements.

Cerebral lateralisation at different stages of facial processing

Two experiments are reported which explore the cerebral lateralisation of different stages of facial processing. In Experiment 1 subjects were briefly presented with either upright or inverted Mooney faces to either the left or right visual field. The subjects' task was to decide whether or not the stimulus had the configuration of a face. The data showed a left visual field superiority in performing this task. In Experiment 2 subjects were briefly presented with line drawings of faces to either the left or right visual field. On half the trials all the facial features were intact whilst in the remainder one feature had been replaced by an anomalous feature in the same position. The subjects were required to detect whether an anomalous feature was present or not and this task produced a right visual field superiority. These data argue against a global right hemisphere superiority in facial processing and suggest, instead, that hemispheric superiority will vary depending on the stage of facial analysis investigated. On the basis of these and other recent findings it would appear that the right hemisphere is advantaged for the holistic stages of facial processing whilst the left-hemisphere has superiority for analysis at the level of individual features. However, the data are ambiguous as to whether the hemispheric differences detected reflect face-specific or general processing characteristics of the cerebral hemispheres.

Familiarity decisions for faces presented to the left and right cerebral hemispheres

Right-handed subjects were asked to decide whether or not faces presented briefly in the RVF or in the LVF were familiar (familiar faces were those of famous people). This task avoids the need for extensive semantic processing or temporary storage involved in conventional naming or identification tasks, and thus eliminates the contribution of such factors to any observed asymmetry. The resulting finding of faster reaction times to LVF faces, with no overall visual hemifield difference in error rates, is taken to indicate a right-hemisphere superiority either in the processes used to construct facial representations or in the accessing of face recognition units, or both.

An investigation of hemispheric asymmetry in size and semantic discriminations and related visual ERPs

The present study examined possible hemispheric differences in discriminations of different sizes of geometric shapes (rectangles) and different meanings of words, and determined whether left and right hemisphere derived visual event related potentials (ERPs) were related to performance. Eighteen right-handed subjects (10 male and 8 female) participated in two separate sessions conducted on different days. The visual ERPs were recorded from over left parietal (P3) and right parietal (P4) scalp locations. Subjects were required to make discriminations of three words (PARE, PAIR, PEAR) and three sizes of rectangles (small, medium, large). Each word and rectangle was singly presented for 40 msec at 1 degree 24 minutes of arc to the left and right of central fixation (LVF and RVF respectively). The major findings were as follows: 1) there were no performance and ERP differences between hemispheres in the verbal task; 2) the left hemisphere excelled in the spatial task; however, ERPs derived from the two hemispheres were similar; 3) subjects experienced greater difficulty in their discriminations of geometric size, as compared to words, regardless of field of presentation. Discrimination of size seemed to have influenced P3 (P300) latency, i.e., it was longer (both hemispheres) when subjects made size discriminations as compared to words. It was proposed that the more difficult discriminations involved in size discrimination required a greater time for stimulus evaluation and that this was reflected in the delayed P3 response.

Right cerebral hemisphere superiority for constructing facial representations

Right-handed people were asked to decide whether or not stimuli presented in the left visual hemifield (LVF) or in the right visual hemifield (RVF) were faces. Manual reaction times and error rates were recorded under three conditions. In Condition A, stimuli were line drawings of faces and moderately scrambled nonfaces made by rearranging the facial features. In Condition B, stimuli were line drawings of faces and highly scrambled nonfaces. In Condition C, stimuli were line drawings of faces and objects. The results show that faces are identified more quickly from the LVF than from the RVF in Condition A (faces vs moderately scrambled nonfaces), with no visual hemifield difference in reaction times to Condition B (faces vs highly scrambled nonfaces) and Condition C (faces vs objects). These findings are taken to indicate that both cerebral hemispheres are able to assign stimuli to the "face" category, but the right hemisphere is better than the left hemisphere at constructing facial representations. This cerebral hemisphere difference in ability to construct facial representations becomes evident when a detailed representation is required (as in Condition A).