Perceptual functions in prosopagnosia

Some patients with prosopagnosia may have an apperceptive basis to their recognition defect. Perceptual abnormalities have been reported in single cases or small series, but the causal link of such deficits to prosopagnosia is unclear. Our goal was to identify candidate perceptual processes that might contribute to prosopagnosia, by subjecting several prosopagnosic patients to a battery of functions that may be necessary for accurate facial perception. We tested seven prosopagnosic patients. Three had unilateral right occipitotemporal lesions, two had bilateral posterior occipitotemporal lesions, and one had right anterior-to-occipital temporal damage along with a small left temporal lesion. These lesions all included the fusiform face area, in contrast to one patient with bilateral anterior temporal lesions. Most patients had impaired performance on face-matching tests and difficulty with subcategory judgments for non-face objects. The most consistent deficits in patients with lesions involving the fusiform face area were impaired perception of spatial relations in dot patterns and reduced contrast sensitivity in the 4 to 8 cycles deg(-1) range. Patients with bilateral lesions were impaired in saturation discrimination. Luminance discrimination was normal in all but two patients, and spatial resolution was uniformly spared. Curvature and line-orientation discrimination were impaired in only one patient, who also had the most difficulty with more basic-level object recognition. We conclude that deficits in luminance, spatial resolution, curvature, line orientation, and contrast at low spatial frequencies are unlikely to contribute to apperceptive prosopagnosia. More relevant may be contrast sensitivity at higher spatial frequencies and the analysis of object spatial structure. Deficits in these functions may impair perception of subtle variations in object shape, and may be one mechanism by which the recognition defect in prosopagnosia can extend to other classes of object subcategorization.     

Gaze behaviour in hereditary prosopagnosia

Prosopagnosia is the inability to recognize someone by the face alone in the absence of sensory or intellectual impairment. In contrast to the acquired form of prosopagnosia we studied the congenital form. Since we could recently show that this form is inherited as a simple monogenic trait we called it hereditary form. To determine whether not only face recognition and neuronal processing but also the perceptual acquisition of facial information is specific to prosopagnosia, we studied the gaze behaviour of four hereditary prosopagnosics in comparison to matched control subjects. This rarely studied form of prosopagnosia ensures that deficits are limited to face recognition. Whereas the control participants focused their gaze on the central facial features, the hereditary prosopagnosics showed a significantly different gaze behaviour. They had a more dispersed gaze and also fixated external facial features. Thus, the face recognition impairment of the hereditary prosopagnosics is reflected in their gaze behaviour.     

Understanding provoked overt recognition in prosopagnosia

Prosopagnosic patients are unable to recognize overtly the faces of familiar people. However, under specific experimental conditions, overt recognition of faces has been induced in some prosopagnosics. This phenomenon of provoked overt recognition has proved challenging for current theories of face recognition. We first describe clinical demonstrations of provoked overt recognition, before highlighting some critical features that any satisfactory explanation of the phenomenon must accommodate. An account of provoked overt recognition is then put forward, couched within the framework of Burton, Bruce, and Johnston's (1990) IAC model of face recognition. This theory is tested by running computer simulations with the model. Finally, the present explanation of provoked overt recognition is scrutinized to discover whether it has implications for rehabilitation work with prosopagnosic patients.     

Implicit familiarity processing in congenital prosopagnosia

A particularly interesting and somewhat puzzling finding in the face‐processing literature is that, despite the absence of overt recognition of most faces, many patients with acquired prosopagnosia (AP) exhibit evidence of intact covert face recognition of the very same faces. This phenomenon has important implications for the understanding of the mechanism underlying AP and, by extension, the mechanism underlying normal face processing. Here, we set out to examine whether individuals with congenital prosopagnosia (CP) exhibit a similar dissociation between overt and covert face recognition. We first confirmed that all six of our CP individuals were significantly impaired in face recognition in comparison with controls. Participants then completed a matching task with both famous and unknown faces in which they decided whether two consecutive images have the same identity or not. Critically, the level of face familiarity was orthogonal to the task at hand and this enabled us to examine whether the familiarity of a face enhanced identity matching, a finding which would implicate implicit face processing. As expected, the CP individuals were slower and less accurate than the control participants. More importantly, like the controls, the CP individuals were faster and more accurate at matching famous compared with unknown faces. Also, for both groups, matching performance on unrecognized famous faces fell at an intermediate level between performance on explicitly recognized famous faces and faces which are unknown. These results provide the first solid evidence for the existence of implicit familiarity processing in CP and suggest that, despite the marked impairment in explicit face recognition, these individuals still have some familiarity representation which manifests in the form of covert recognition. We discuss possible models to account for the apparent dissociation of overt and covert face processing in CP.     

Visual agnosia and prosopagnosia in childhood: a prospective case study.

Selective impairments in visual processing are well documented in adults but rarely reported in children. The few childhood cases reported are mostly retrospective accounts with little attention paid to developmental, assessment or management issues. We report a prospective case study of a boy with prosopagnosia and visual processing deficits of presumed developmental origin. At the age of 4 years, AL presented with a range of cognitive and visual recognition deficits. Subsequent assessments revealed an evolving pattern in visual recognition and dissociations between developing skills. At the age of 7 AL has impairments in early perceptual analysis, visual organisation and in complex visual processing. Although he can identify facial features and match faces he is unable to recognise familiar faces. His reading and spelling are developing normally. The nature of his deficits and his progress are discussed within a cognitive neuropsychological framework.     

Symptoms of Meares-Irlen/Visual Stress Syndrome in subjects diagnosed with Chronic Fatigue Syndrome

Several diagnostic symptoms of the visual-processing deficit Meares-Irlen/Visual Stress Syndrome are remarkably similar to symptom manifestations reported by individuals with chronic fatigue syndrome (CFS). We surveyed the specific incidences of nine widely-recognised symptoms of visual stress (VS) in a group of subjects (n = 20) previously diagnosed with CFS. The presence of each symptom of VS in the CFS group was compared to its respective presence in both an age and sex matched healthy comparison group (n = 46), and an age and sex matched group comprised of individuals (n = 14) diagnosed with VS. Results showed the frequencies of all nine VS symptoms in the CFS-diagnosed group to be significantly higher (p = .032 – p < .0005) than in the comparison group, with only two symptoms being statistically less frequent in the CFS group than in the VS-diagnosed group. The average number of VS symptoms reported by the CFS group was also significantly higher than the comparison group, yet not significantly different from the VS group. Thus, the occurrence of VS symptoms in subjects diagnosed with CFS appears to be far greater than previously reported, which in turn may indicate the interplay of some yet to be identified underlying factor(s) common to both conditions.     

Covert face recognition in prosopagnosia: A review

Prosopagnosia, a spectacular face agnosia, is generally detected and discussed on the basis of explicit or overt performance of the subjects. However, recent observations suggest that an overt response is probably not sufficient to determine what is and what is not preserved in the cognitive processing of faces by prosopagnosia. Indeed, signs of covert knowledge have been evidenced in some, but not all, subjects, indicating that they are still able to use representations they cannot use overtly. Empirical data, showing that the nature of prosopagnosia is a more complex phenomenon than has been thought and that the processing models should be adjusted accordingly, are reviewed.     

Further observations on the nature of prosopagnosia

Two new cases of prosopagnosia are described and compared with pertinent clinical material from the English language literature. The interpretation of this disorder most compatible with the clinical data appears to us to be that there is an underspecification of visuoperceptive information preventing both the formation of significant face images and the retrieval of well-known face memoranda existing within a relatively intact visual remote memory store. Failure of formation of immediate memoranda of similarly complex visual images is also commonly observed but does not seem to be a requirement for the symptom of prosopagnosia. Conceptualizing this abnormality as simply a material specific visual agnosia of images beyond the classifier level would still appear to be acceptable if less informative.     

Preservation of mouth region processing in two cases of prosopagnosia

Although most adults are considered experts in face recognition, brain trauma can produce a selective loss in this ability, a condition referred to as prosopagnosia. This study examined the processing strategies of prosopagnosic patients LR and HH using the Face Dimensions Test. In this test, featural and configural information in the upper and lower halves of the face was parametrically varied and sensitivity to these changes measured. We found that relative to age‐matched control participants, LR and HH exhibited an impaired ability to discriminate differences in the eye region, but a preserved ability to detect featural and configural differences in the mouth region. This pattern of impairment and sparing was demonstrated in tests of direct perception and immediate memory. The obtained findings demonstrate that prosopagnosia does not necessarily cause a global impairment to face perception, but a selective impairment to the perception of information in the upper half of the face.     

Electrodermal discrimination of familiar but not unfamiliar faces in prosopagnosia

It has been previously shown that prosopagnosics can electrodermally "recognize" faces they cannot verbally identify and with which they feel no familiarity. This study extended previous results by showing that electrodermal discrimination of faces exists only on a famous face identification task, and not on a matching-to-sample task involving unfamiliar faces. This suggests that electrodermal recognition reflects the activation of stored identity-specific information built up on the basis of past contact with faces, and provides a psychophysiological distinction between familiar and unfamiliar face processing. Implications for cognitive models of face recognition, and for understanding the nature of prosopagnosia, are discussed.     

Aberrant pattern of scanning in prosopagnosia reflects impaired face processing

Visual scanpath recording was used to investigate the information processing strategies used by a prosopagnosic patient, SC, when viewing faces. Compared to controls, SC showed an aberrant pattern of scanning, directing attention away from the internal configuration of facial features (eyes, nose) towards peripheral regions (hair, forehead) of the face. The results suggest that SC's face recognition deficit can be linked to an inability to assemble an accurate and unified face percept due to an abnormal allocation of attention away from the internal face region. Extraction of stimulus attributes necessary for face identity recognition is compromised by an aberrant face scanning pattern.     

Dissociation of facial attractiveness and distinctiveness processing in congenital prosopagnosia

According to the influential model of Bruce and Young (1986) socially relevant facial information is processed separately from facial information leading to individual face recognition. In recent years functional imaging has identified a network of distinct occipitotemporal cortex areas for the processing of these two kinds of information. Functionally it is not clear at which processing level the “social” and the “recognition” pathways diverge. The study of subjects with a profound face recognition and learning deficit (congenital prosopagnosia—cPA) promises for a better understanding of this issue. We therefore tested the perception of attractiveness (a cue of prime social importance) and distinctiveness (a facial feature related to recognition) in 14 people with cPA. Although attractiveness ratings were highly consistent with controls, cPA subjects' distinctiveness ratings showed random patterns. This dissociation of normal attractiveness processing and impaired distinctiveness processing in cPA helps to specifies the nature of the impairment in this condition while shedding light on the functional architecture of normal face processing.     

Developmental prosopagnosia: a study of three patients

We studied perception in three patients with prosopagnosia of childhood onset. All had trouble with other 'within-category' judgments. All were deficient on face matching tests and severely impaired on tests of perception of the spatial relations of facial features and abstract designs, indicating a deficit in the encoding of coordinate relationships, similar to adult-onset prosopagnosia with lesions of the fusiform face area. Two had difficulty perceiving feature colour, which correlated with reduced luminance sensitivity. In contrast to adult-onset patients, saturation discrimination was spared in two and spatial resolution impaired in two. Curvature discrimination was relatively spared. Contrast sensitivity showed variable reductions at different spatial frequencies. We conclude that developmental prosopagnosia is similar to the adult-onset form in encoding deficits for the spatial arrangement of facial elements. Deficits in luminance perception and spatial resolution are more associated with defective encoding for basic object-level recognition, as shown on tests of object and spatial perception.     

Cognitive heterogeneity in genetically based prosopagnosia: A family study

Congenital prosopagnosia (CP) is a selective difficulty in recognizing familiar faces that is present from birth. There is mounting evidence for a familial factor in CP, possibly due to a simple autosomal inheritance pattern. However, potential candidate genes remain to be established, and the question whether genetically based CP is a single trait, or a cluster of related subtypes differing in the pattern of impairments to specific components of the face‐processing system, remains unanswered. In addition, since the great majority of so far described cases with CP were adult at the time of investigation, it remains unknown which specific aspects of face processing are impaired in small children with CP. Here we present the first study that specifically addresses these questions by elucidating the specific mechanisms underlying face‐recognition impairments in seven individuals with CP (aged 4–87 years) belonging to four generations of the same family. Our results indicate that genetically based CP is not a single trait but a cluster of related subtypes, since the pattern of impairments to specific components of the face‐processing system varies in individuals belonging to the same family. In addition, we show that the heterogeneity of the cognitive profile in CP with respect to specific aspects of face processing is apparent from early childhood.     

Neural and genetic foundations of face recognition and prosopagnosia

Faces are of essential importance for human social life. They provide valuable information about the identity, expression, gaze, health, and age of a person. Recent face‐processing models assume highly interconnected neural structures between different temporal, occipital, and frontal brain areas with several feedback loops. A selective deficit in the visual learning and recognition of faces is known as prosopagnosia, which can be found both in acquired and congenital form. Recently, a hereditary sub‐type of congenital prosopagnosia with a very high prevalence rate of 2.5% has been identified. Recent research results show that hereditary prosopagnosia is a clearly circumscribed face‐processing deficit with a characteristic set of clinical symptoms. Comparing face processing of people of prosopagnosia with that of controls can help to develop a more conclusive and integrated model of face processing. Here, we provide a summary of the current state of face processing research. We also describe the different types of prosopagnosia and present the set of typical symptoms found in the hereditary type. Finally, we will discuss the implications for future face recognition research.     

Alcohol intoxicated witnesses' interpretation of social behavior in intimate partner violence

Alcohol intoxication affects social information processing, though research is scarce regarding how alcohol affected eyewitnesses' perception of social interaction within an applied forensic context. In the present study, the effects of alcohol intoxication on eyewitnesses' perception of interaction in intimate partner violence (IPV) were investigated. The participants (n = 152) were randomized to an experimental (alcohol) or control group (juice). After consumption, they viewed a filmed IPV scenario where both interacting parties were confrontational. Afterwards, they rated the involved parties' behavior. Several behaviors were perceived in a similar manner by intoxicated and sober participants, but intoxicated participants perceived both parties' attacking behaviors and some of the man's prosocial behaviors differently than sober participants. Hence, alcohol affected some, but not all, kinds of social behaviors investigated in the present study. This would be of interest to legal praxis and to future studies on intoxicated witnesses to interpersonal violence.     

Faces as objects of non-expertise: processing of thatcherised faces in congenital prosopagnosia

Congenital prosopagnosia (cPA) is a severe disorder in recognising familiar faces, a human characteristic that is presumably innate, without any macro-spatial brain anomalies. Following the idea that cPA is based on deficits of configural face processing, we used a speeded grotesqueness decision task with thatcherised faces, since the Thatcher illusion can serve as a test of configural disruption (Lewis and Johnston, 1997 Perception 26 225-227). The time needed to report the grotesqueness of a face in relation to orientation showed dissociate patterns between a group of fourteen people with cPA and a group of matched controls: whereas the RTs of controls followed a strong sigmoid function depending on rotation from the upright orientation, the RTs of people with cPA showed a much weaker sigmoid trend approaching a linear function. The latter result is interpreted as a diagnostic sign of impaired configural processing, being the primary cause of the absence of 'face expertise' in prosopagnosia.     

Underestimation of length by subjects in motion.

To check a prior observation, in the present experiment, subjects made estimates of the lengths of both the guidelines and the spaces between guidelines on automotive highways so the magnitude of the illusion could be more accurately determined. Ten males and ten females were individually tested at 0 and 60 mph. At 60 mph, spaces were estimated with an error of 85%; lines were estimated with an error of 72%. Combining data for both stimuli, an error of 78% results, which corresponds to underestimation by a factor of 4.67. This illusory effect is considerably greater than that of the moon illusion, considered by many the most powerful of the classical illusions.     

The biasing of figure-ground assignment by shading cues for objects and faces in prosopagnosia

Prosopagnosia is defined by impaired recognition of the identity of specific faces. Whether the perception of faces at the categorical level (recognizing that a face is a face) is also impaired to a lesser degree is unclear. We examined whether prosopagnosia is associated with impaired detection of facial contours in a bistable display, by testing a series of five prosopagnosic patients on a variation of Rubin's vase illusion, in which shading was introduced to bias perception towards either the face or the vase. We also included a control bistable display in which a disc or an aperture were the two possible percepts. With the control disc/aperture test, prosopagnosic patients did not generate a normal sigmoid function, but a U-shaped function, indicating that they perceived the shading but had difficulty in using the shading to make the appropriate figure-ground assignment. While controls still generated a sigmoid function for the vase/face test, prosopagnosic patients showed a severe impairment in using shading to make consistent perceptual assignments. We conclude that prosopagnosic patients have difficulty in using shading to segment figures from background correctly, particularly with complex stimuli like faces. This suggests that a subtler defect in face categorization accompanies their severe defect in face identification, consistent with predictions of computational models and recent data from functional imaging.