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.     

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.     

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.     

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.     

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.     

The role of holistic face processing in acquired prosopagnosia: evidence from the composite face effect

Faces are processed more holistically than other objects, and it has been suggested that the loss of holistic face processing causes acquired prosopagnosia. Support for this hypothesis comes from several cases who failed to show holistic face effects as well as the absence of reports of prosopagnosics with unequivocally normal holistic face perception. The current study examines the relationship between holistic face processing and prosopagnosia by testing seven acquired prosopagnosics with the face composite task, a classic measure of holistic face processing. To enhance the robustness of the findings, each prosopagnosic was tested with two versions of the composite task showing upright faces. We also tested an inverted condition to exclude the possibility that more general factors account for composite effects for upright faces. Four of the seven acquired prosopagnosic participants showed consistent upright face composite effects with minimal inverted face composite effects. We conclude that severe face processing deficits can co-occur with intact holistic face processing and that factors other than a loss of holistic processing contribute to the perceptual and recognition deficits in acquired prosopagnosia.     

Covert processing of faces in prosopagnosia is restricted to facial expressions: evidence from cross-modal bias

We present a single case study of a brain-damaged patient, AD, suffering from visual face and object agnosia, with impaired visual perception and preserved mental imagery. She is severely impaired in all aspects of overt recognition of faces as well as in covert recognition of familiar faces. She shows a complete loss of processing facial expressions in recognition as well as in matching tasks. Nevertheless, when presented with a task where face and voice expressions were presented concurrently, there was a clear impact of face expressions on her ratings of the voice. The cross-modal paradigm used here and validated previously with normal subjects (de Gelder & Vroomen, 1995, 2000), appears as a useful tool in investigating spared covert face processing in a neuropsychological perspective, especially with prosopagnosic patients. These findings are discussed against the background of different models of the covert recognition of face expressions.     

Face gender recognition in developmental prosopagnosia: Evidence for holistic processing and use of configural information

Face identification deficits in developmental prosopagnosics (DPs) have been thought to be due to general difficulties with processing configural face information and integrating configural and parts information into a coherent whole (holistic processing). Gender recognition provides a further opportunity to more fully examine this issue as this ability may be intact in DPs and it has been shown to depend on processing configural information and holistic processing in neurotypical individuals. In the present study we first determined that, indeed, gender discrimination performance was similar in DPs and controls. Second, we found that inversion and scrambling (which we propose measures holistic processing and sensitivity to configural information, respectively) produced comparable deficits in DPs and controls, suggesting that both groups use holistic processing and configural information to recognize gender. This indicates that holistic processing and using configural face information are not general impairments in DP and may be more specific to face identity.     

Impaired face detection may explain some but not all cases of developmental prosopagnosia

Developmental prosopagnosia (DP) is defined by severe face recognition difficulties due to the failure to develop the visual mechanisms for processing faces. The two‐process theory of face recognition (Morton & Johnson, 1991) implies that DP could result from a failure of an innate face detection system; this failure could prevent an individual from then tuning higher‐level processes for face recognition (Johnson, 2005). Work with adults indicates that some individuals with DP have normal face detection whereas others are impaired. However, face detection has not been addressed in children with DP, even though their results may be especially informative because they have had less opportunity to develop strategies that could mask detection deficits. We tested the face detection abilities of seven children with DP. Four were impaired at face detection to some degree (i.e. abnormally slow, or failed to find faces) while the remaining three children had normal face detection. Hence, the cases with impaired detection are consistent with the two‐process account suggesting that DP could result from a failure of face detection. However, the cases with normal detection implicate a higher‐level origin. The dissociation between normal face detection and impaired identity perception also indicates that these abilities depend on different neurocognitive processes.     

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.     

Word processing in the parafoveal region

This study examined the role of words viewed in the parafoveal region during reading. In contrast to previous work, the present experiments used a reading-aloud paradigm that was postulated to encourage letter-to-sound processing, as is typical for beginning readers and for skilled readers who are reading difficult material. The three experiments in this study examined the role of orthographic and semantic information in the parafoveal region on the processing of a word in the foveal region. For this, two words, one in the foveal region and the other in the parafoveal region, were presented side by side to resemble normal reading. Participants were instructed to read aloud the word on the left side, ignoring the word on the right side. Experiments 1 and 2 showed that the presence of a word in the parafoveal region slowed naming of target words, and that this delay was attributable to linguistic interference. This pattern indicates that the information in the parafoveal region affect the processing of the target. Experiment 3 showed an effect of parafoveal semantic information on processing of the target word. In sum the results of the current study suggest that information in the parafoveal region appears to be linguistically processed but to a weaker degree than the focused word. In sum, the results of the experiments in the current study indicate that the influence of parafoveal information is quite lexical and semantic information in the parafoveal region affects processing of the target in the foveal region.     

Preservation of person‐specific knowledge in semantic memory disorder: A longitudinal investigation in two cases of dementia

The double dissociation involving person‐specific and general semantic knowledge is supported by numerous patient studies, though cases with preservation of the former are few. In this paper, we report longitudinal data from two cases. Their knowledge in both domains was preserved at the start of the investigation, but progressive deterioration was primarily observed on tests of general semantics. These data strengthen the evidence‐base for preservation of person‐specific knowledge in semantic memory disorder, and support its separate representation from object knowledge.     

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.     

Impaired holistic and analytic face processing in congenital prosopagnosia: Evidence from the eye-contingent mask/window paradigm

There is abundant evidence that face recognition, in comparison to the recognition of other objects, is based on holistic processing rather than analytic processing. One line of research that provides evidence for this hypothesis is based on the study of people who experience pronounced difficulties in visually identifying conspecifics on the basis of their face. Earlier, we developed a behavioural paradigm to directly test analytic vs. holistic face processing. In comparison to a to be remembered reference face stimulus, one of two test stimuli was either presented in full view, with an eye-contingently moving window (only showing the fixated face feature, and therefore only affording analytic processing), or with an eye-contingently moving mask or scotoma (masking the fixated face feature, but still allowing holistic processing). In the present study we use this paradigm (that we used earlier in acquired prosopagnosia) to study face perception in congenital prosopagnosia (people having difficulties recognizing faces from birth on, without demonstrable brain damage). We observe both holistic and analytic face processing deficits in people with congenital prosopagnosia. Implications for a better understanding, both of congenital prosopagnosia and of normal face perception, are discussed.     

Symptoms of prosopagnosia in intoxicated subjects.

Two experiments were made to test whether a blood ethanol concentration of about 1 g ethanol per kg blood influences the ability to recognize faces which were shown 24 hours earlier. 18 subjects who saw the faces for the first time when sober and whose task it was to recognize the faces when under the influence of alcohol, recognized the faces significantly less frequently than controls. The controls saw the faces for the first time when sober and their task was to recognize the faces later when also in a sober state. When 20 sober subjects had to recognize faces which they had seen 24 hours earlier under the influence of alcohol, they recognized the faces significantly less frequently than controls. 18 subjects to whom visual forms were shown when under the influence of alcohol and who had to recognize these forms 24 hours later when sober again performed like subjects who had to recognize faces under identical experimental conditions. Subjects who saw the forms, however, in a sober state and who had to recognize these forms when intoxicated performed significantly better than subjects who had to recognize faces under identical experimental conditions. In additional experiments, it was shown that alcohol did not influence ability to compare simultaneously presented faces. Intoxicated subjects' reduced abilities to recognize faces is regarded as a symptom of prosopagnosia since it cannot be explained by a reduced ability to recognize forms or to compare faces.     

Holistic processing of shape cues in face identification: Evidence from face inversion,composite faces,and acquired prosopagnosia

According to a classical functional architecture of face processing (Bruce & Young, 1986), sex processing on faces is a parallel function to individual face recognition. One consequence of the model is thus that sex categorization on faces is not influenced by face familiarity. However, the behavioural and neuro-psychological evidences supporting this dissociation are yet equivocal. To test the independence between sex processing on faces and familiar face recognition, familiar (learned) faces were morphed with new faces, generating facial continua of visual similarity to familiar faces. First, a pilot experiment shown that subjects familiarized with one extreme of the face continuum roughly perceive one half of the continuum (60 to 100% of visual similarity to familiar faces) as made of familiar faces and the other part as unfamiliar. In the experiment proper, subjects were familiarized with faces and tested in a sex decision task made on faces at the different steps of the continua. Subjects were significantly quicker at telling the sex of faces perceived as familiar (60-100%), and the effect was not observed in a control (untrained) group. These results indicate that familiar face representations are activated before sex categorization is completed, and can facilitate this processing. The nature of the interaction between sex categorization on faces and familiar face recognition is discussed.     

Holistic processing impairment can be restricted to faces in acquired prosopagnosia: Evidence from the global/local Navon effect

Previous studies have shown that acquired prosopagnosia is characterized by impairment at holistic/configural processing. However, this view is essentially supported by studies performed with patients whose face recognition difficulties are part of a more general visual (integrative) agnosia. Here, we tested the patient PS, a case of acquired prosopagnosia whose face‐specific recognition difficulties have been related to the inability to process individual faces holistically (absence of inversion, composite, and whole–part effects with faces). Here, we show that in contrast to this impairment, the patient presents with an entirely normal response profile in a Navon hierarchical letter task: she was as fast as normal controls, faster to identify global than local letters, and her sensitivity to global interference during identification of local letters was at least as large as normal observers. These observations indicate that holistic processing as measured with global/local interference in the Navon paradigm is functionally distinct from the ability to perceive an individual face holistically.     

Face recognition and emotional valence: processing without awareness by neurologically intact participants does not simulate covert recognition in prosopagnosia

Covert face recognition in neurologically intact participants was investigated with the use of very brief stimulus presentation to prevent awareness of the stimulus. In Experiment 1, skin conductance response (SCR) to photographs of celebrity and unfamiliar faces was recorded; the faces were displayed for 220 msec and for 17 msec in a within-participants design. SCR to faces presented for 220 msec was larger and more likely to occur with familiar faces than with unfamiliar faces. Face familiarity did not affect the SCR to faces presented for 17 msec. SCR was larger for faces of good than for faces of evil celebrities presented for 17 msec, but valence did not affect SCR to faces displayed for 220 msec. In Experiment 2, associative priming was found in a face familiarity decision task when the prime face was displayed for 220 msec, but no facilitation occurred when primes were presented for 17 msec. In Experiment 3, participants were able to differentiate evil and good faces presented without awareness in a two-alternative forced-choice decision. The results provide no evidence of familiarity detection outside awareness in normal participants and suggest that, contrary to previous research, very brief presentation to neurologically intact participants is not a useful model for the types of covert recognition found in prosopagnosia. However, a response based on affective valence appears to be available from brief presentation.