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

Which components of famous people recognition are lateralized? A study of face, voice and name recognition disorders in patients with neoplastic or degenerative damage of the right or left anterior temporal lobes

We administered to large groups of patients with neoplastic or degenerative damage affecting the right or left ATL, the 'Famous People Recognition Battery' (FPRB), in which subjects are required to recognize the same 40 famous people through their faces, voices and names, to clarify which components of famous people recognition are lateralized. At the familiarity level, we found, as expected, a dissociation between a greater impairment of patients with right ATL lesions on the non-verbal (face and voice) recognition modalities and of those with left ATL lesions on name familiarity. Equally expected were results obtained at the naming level, because the worse naming scores for faces and voices were observed in left-sided patients. Less foregone were, for two reasons, results obtained at the semantic level. First, no difference was found between the two hemispheric groups when scores obtained on the verbal (name) and non-verbal (face and voice) recognition modalities were account for. Second, the face and voice recognition modalities showed a different degree of right lateralization. All groups of patients showed, indeed, both at the familiarity and at the semantic level, a greater difficulty in the recognition of voices regarding faces, but this difference reached significance only in patients with right ATL lesions, suggesting a greater right lateralization of the more complex task of voice recognition. A model aiming to explain the greater right lateralization of the more perceptually demanding voice modality of person recognition is proposed.

Measuring the response to visually presented faces in the human lateral prefrontal cortex

Neuroimaging studies identify multiple face-selective areas in the human brain. In the current study, we compared the functional response of the face area in the lateral prefrontal cortex to that of other face-selective areas. In Experiment 1, participants (n = 32) were scanned viewing videos containing faces, bodies, scenes, objects, and scrambled objects. We identified a face-selective area in the right inferior frontal gyrus (rIFG). In Experiment 2, participants (n = 24) viewed the same videos or static images. Results showed that the rIFG, right posterior superior temporal sulcus (rpSTS), and right occipital face area (rOFA) exhibited a greater response to moving than static faces. In Experiment 3, participants (n = 18) viewed face videos in the contralateral and ipsilateral visual fields. Results showed that the rIFG and rpSTS showed no visual field bias, while the rOFA and right fusiform face area (rFFA) showed a contralateral bias. These experiments suggest two conclusions; firstly, in all three experiments, the face area in the IFG was not as reliably identified as face areas in the occipitotemporal cortex. Secondly, the similarity of the response profiles in the IFG and pSTS suggests the areas may perform similar cognitive functions, a conclusion consistent with prior neuroanatomical and functional connectivity evidence.

The Human Posterior Superior Temporal Sulcus Samples Visual Space Differently From Other Face-Selective Regions

Neuroimaging studies show that ventral face-selective regions, including the fusiform face area (FFA) and occipital face area (OFA), preferentially respond to faces presented in the contralateral visual field (VF). In the current study we measured the VF response of the face-selective posterior superior temporal sulcus (pSTS). Across 3 functional magnetic resonance imaging experiments, participants viewed face videos presented in different parts of the VF. Consistent with prior results, we observed a contralateral VF bias in bilateral FFA, right OFA (rOFA), and bilateral human motion-selective area MT+. Intriguingly, this contralateral VF bias was absent in the bilateral pSTS. We then delivered transcranial magnetic stimulation (TMS) over right pSTS (rpSTS) and rOFA, while participants matched facial expressions in both hemifields. TMS delivered over the rpSTS disrupted performance in both hemifields, but TMS delivered over the rOFA disrupted performance in the contralateral hemifield only. These converging results demonstrate that the contralateral bias for faces observed in ventral face-selective areas is absent in the pSTS. This difference in VF response is consistent with face processing models proposing 2 functionally distinct pathways. It further suggests that these models should account for differences in interhemispheric connections between the face-selective areas across these 2 pathways.

Understanding face identification through within-person variability in appearance: Introduction to a virtual special issue

In the effort to determine the cognitive processes underlying the identification of faces, the dissimilarities between images of different people have long been studied. In contrast, the inherent variability between different images of the same face has either been treated as a nuisance variable that should be eliminated from psychological experiments or it has not been considered at all. Over the past decade, research efforts have increased substantially to demonstrate that this within-person variation is meaningful and can give insight into various processes of face identification, such as identity matching, face learning, and familiar face recognition. In this virtual special issue of the Quarterly Journal of Experimental Psychology, we explain the importance of within-person variability for face identification and bring together recent relevant articles published in the journal.

A functional dissociation of face-, body- and scene-selective brain areas based on their response to moving and static stimuli

The human brain contains areas that respond selectively to faces, bodies and scenes. Neuroimaging studies have shown that a subset of these areas preferentially respond more to moving than static stimuli, but the reasons for this functional dissociation remain unclear. In the present study, we simultaneously mapped the responses to motion in face-, body- and scene-selective areas in the right hemisphere using moving and static stimuli. Participants (N = 22) were scanned using functional magnetic resonance imaging (fMRI) while viewing videos containing bodies, faces, objects, scenes or scrambled objects, and static pictures from the beginning, middle and end of each video. Results demonstrated that lateral areas, including face-selective areas in the posterior and anterior superior temporal sulcus (STS), the extrastriate body area (EBA) and the occipital place area (OPA) responded more to moving than static stimuli. By contrast, there was no difference between the response to moving and static stimuli in ventral and medial category-selective areas, including the fusiform face area (FFA), occipital face area (OFA), amygdala, fusiform body area (FBA), retrosplenial complex (RSC) and parahippocampal place area (PPA). This functional dissociation between lateral and ventral/medial brain areas that respond selectively to different visual categories suggests that face-, body- and scene-selective networks may be functionally organized along a common dimension.

Lateralized Repetition Priming for Familiar Faces: Evidence for Asymmetric Interhemispheric Cooperation

Repetition priming refers to facilitated recognition of stimuli that have been seen previously. Although a great deal of work has examined the properties of repetition priming for familiar faces, little has examined the neuroanatomical basis of the effect. Two experiments are presented in this paper that combine the repetition priming paradigm with a divided visual field methodology to examine lateralized recognition of familiar faces. In the first experiment participants were presented with prime faces unilaterally to each visual field and target faces foveally. A significant priming effect was found for prime faces presented to the right hemisphere, but not for prime faces presented to the left hemisphere. In Experiment 2, prime and target faces were presented unilaterally, either to the same visual field or to the opposite visual field (i.e., either within hemisphere or across hemispheres). A significant priming effect was found for the within right hemisphere condition, but not for the within left hemisphere condition, replicating the findings of the first experiment. Priming was also found in both of the across hemispheres conditions, suggesting that interhemispheric cooperation occurs to aid recognition. Taken in combination these experiments provide two main findings. First, an asymmetric repetition priming effect was found, possibly as a result of asymmetric levels of activation following recognition of a prime face, with greater priming occurring within the right hemisphere. Second, there is evidence for asymmetric interhemispheric cooperation with transfer of information from the right hemisphere to the left hemisphere to facilitate recognition.

The Role of External Features in Face Recognition with Central Vision Loss

PURPOSE

We evaluated how the performance of recognizing familiar face images depends on the internal (eyebrows, eyes, nose, mouth) and external face features (chin, outline of face, hairline) in individuals with central vision loss.

METHODS

In experiment 1, we measured eye movements for four observers with central vision loss to determine whether they fixated more often on the internal or the external features of face images while attempting to recognize the images. We then measured the accuracy for recognizing face images that contained only the internal, only the external, or both internal and external features (experiment 2) and for hybrid images where the internal and external features came from two different source images (experiment 3) for five observers with central vision loss and four age-matched control observers.

RESULTS

When recognizing familiar face images, approximately 40% of the fixations of observers with central vision loss was centered on the external features of faces. The recognition accuracy was higher for images containing only external features (66.8 ± 3.3% correct) than for images containing only internal features (35.8 ± 15.0%), a finding contradicting that of control observers. For hybrid face images, observers with central vision loss responded more accurately to the external features (50.4 ± 17.8%) than to the internal features (9.3 ± 4.9%), whereas control observers did not show the same bias toward responding to the external features.

CONCLUSIONS

Contrary to people with normal vision who rely more on the internal features of face images for recognizing familiar faces, individuals with central vision loss show a higher dependence on using external features of face images.

Response inhibition is modulated by functional cerebral asymmetries for facial expression perception

The efficacy of executive functions is critically modulated by information processing in earlier cognitive stages. For example, initial processing of verbal stimuli in the language-dominant left-hemisphere leads to more efficient response inhibition than initial processing of verbal stimuli in the non-dominant right hemisphere. However, it is unclear whether this organizational principle is specific for the language system, or a general principle that also applies to other types of lateralized cognition. To answer this question, we investigated the neurophysiological correlates of early attentional processes, facial expression perception and response inhibition during tachistoscopic presentation of facial “Go” and “Nogo” stimuli in the left and the right visual field (RVF). Participants committed fewer false alarms after Nogo-stimulus presentation in the left compared to the RVF. This right-hemispheric asymmetry on the behavioral level was also reflected in the neurophysiological correlates of face perception, specifically in a right-sided asymmetry in the N170 amplitude. Moreover, the right-hemispheric dominance for facial expression processing also affected event-related potentials typically related to response inhibition, namely the Nogo-N2 and Nogo-P3. These findings show that an effect of hemispheric asymmetries in early information processing on the efficacy of higher cognitive functions is not limited to left-hemispheric language functions, but can be generalized to predominantly right-hemispheric functions.

Visual field bias in hearing and deaf adults during judgments of facial expression and identity

The dominance of the right hemisphere during face perception is associated with more accurate judgments of faces presented in the left rather than the right visual field (RVF). Previous research suggests that the left visual field (LVF) bias typically observed during face perception tasks is reduced in deaf adults who use sign language, for whom facial expressions convey important linguistic information. The current study examined whether visual field biases were altered in deaf adults whenever they viewed expressive faces, or only when attention was explicitly directed to expression. Twelve hearing adults and 12 deaf signers were trained to recognize a set of novel faces posing various emotional expressions. They then judged the familiarity or emotion of faces presented in the left or RVF, or both visual fields simultaneously. The same familiar and unfamiliar faces posing neutral and happy expressions were presented in the two tasks. Both groups were most accurate when faces were presented in both visual fields. Across tasks, the hearing group demonstrated a bias toward the LVF. In contrast, the deaf group showed a bias toward the LVF during identity judgments that shifted marginally toward the RVF during emotion judgments. Two secondary conditions tested whether these effects generalized to angry faces and famous faces and similar effects were observed. These results suggest that attention to facial expression, not merely the presence of emotional expression, reduces a typical LVF bias for face processing in deaf signers.

Hemispheric resource availability influences face perception: a multiple resource approach to social perception

Two experiments tested the hypothesis that social perception recruits distinct limited-capacity processing resources that are distinguished by the cerebral hemispheres. To test this hypothesis, social perception efficiency was assessed after relevant hemispheric processing resources were depleted. In Experiment 1 prime faces were unilaterally presented for 30 ms, after which centrally presented target faces were categorised by sex. In Experiment 2 prime faces were unilaterally presented for 80 ms after which centrally presented target faces were categorised by fame. Results showed that sex categorisation was slower after primes were presented in the right versus left visual field, and that fame categorisation was slower after familiar primes were presented in the left versus right visual field. The results support a multiple resource account of social perception in which the availability of resources distributed across the cerebral hemispheres influences social perception.

Laterality in Familiar Face Recognition

An extensive series of experiments has recently led to the hypothesis that face recognition, which had been considered a right-hemisphere specialization, may actually be bilaterally processed in the two hemispheres. In the present study an attempt was made to solve the conundrum of the laterality of face recognition by performing a meta-analysis on studies of familiar face recognition. Results of six studies measuring reaction time of familiar face naming and of eleven studies measuring accuracy of familiar face naming were transformed to standard Z scores. The average Z scores for reaction time and for accuracy were then tested for their significance. The results suggested that face recognition is not lateralized. This conclusion is consistent with theories of bihemispheric cognitive resources and with the latest brain-imaging data.

TMS Evidence for the Involvement of the Right Occipital Face Area in Early Face Processing

Extensive research has demonstrated that several specialized cortical regions respond preferentially to faces. One such region, located in the inferior occipital gyrus, has been dubbed the occipital face area (OFA). The OFA is the first stage in two influential face-processing models, both of which suggest that it constructs an initial representation of a face, but how and when it does so remains unclear. The present study revealed that repetitive transcranial magnetic stimulation (rTMS) targeted at the right OFA (rOFA) disrupted accurate discrimination of face parts but had no effect on the discrimination of spacing between these parts. rTMS to left OFA had no effect. A matched part and spacing discrimination task that used house stimuli showed no impairment. In a second experiment, rTMS to rOFA replicated the face-part impairment but did not produce the same effect in an adjacent area, the lateral occipital cortex. A third experiment delivered double pulses of TMS separated by 40 ms at six periods after stimulus presentation during face-part discrimination. Accuracy dropped when pulses were delivered at 60 and 100 ms only. These findings indicate that the rOFA processes face-part information at an early stage in the face-processing stream.

Interplay between familiarity and orientation in face processing: An ERP study

In order to tap the electrophysiological correlates of the perceptual and structural encoding stages of face processing, we investigated how inversion and familiarity affect the face-specific event-related potentials (ERPs) components. ERPs were recorded while participants performed a familiarity judgment task with upright and inverted photographs of famous and unknown faces. The early P100 component was found to be sensitive to facial configuration that is disrupted by face inversion. Noteworthy, in addition to the ongoing effect of orientation, an effect of familiarity, although limited to upright faces, emerged at the processing stage indexed by N170. Later on, as witnessed by the P250 component, the familiarity effect was generalized to both upright and inverted faces with a larger amplitude for inverted famous faces. All in all, the present results suggest that the face structural encoding stage is cognitively permeable by higher-order factors such as familiarity, especially when familiarity is crucial for mastering the task. From a more general viewpoint, these results indicate that face processing is subserved by multiple mechanisms in which structural (i.e. orientation) and semantic (i.e. familiarity) factors begin to interact at early processing stages with different time courses. The electrophysiological correlates of these mechanisms are documented by the differential involvement of the major ERP components in the "familiarity check". With upright faces familiarity affects the N170 component, while with inverted faces it affects later components, in keeping with a prolonged time course of the familiarity decision when orientation is not upright.

Face familiarity feelings, the right temporal lobe and the possible underlying neural mechanisms

A comprehensive review was made of the relationships between right hemisphere and face familiarity feelings, taking separately into account: (a) studies of patients with unilateral lesions of the anterior or the posterior parts of the right and left temporal lobes, who showed a familiar people recognition disorder, (b) studies of right and left brain-damaged patients, presenting an increased familiarity for unknown persons or abnormal familiarity feelings for well known people, (c) results of studies conducted in normal subjects to evaluate the lateralization of face familiarity feelings. In this last section, we separately reviewed: results obtained by means of separate presentation of familiar and unfamiliar faces to the right and left visual fields; lateralization of event-related potentials evoked by familiar vs unfamiliar faces; results of activation studies presenting familiar and unfamiliar faces. Taken together, results of this review have shown that face familiarity feelings are specifically generated by the right hemisphere. Clinical and neurophysiological data suggest that familiarity feelings: (1) are probably due to a lateralized subcortical route, allowing a first, unconscious, global recognition of familiar faces and (2) facilitate the subsequent distinction of known faces (unconsciously detected) from unfamiliar faces. Results of the review have also shown that the right frontal areas play an important role in the production or monitoring of inappropriate familiarity decisions.

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.

Interhemispheric cooperation for familiar but not unfamiliar face processing

Evidence for interhemispheric cooperation during language processing has been demonstrated for words, but not for meaningless pseudowords. Specifically, responses were found to be faster and more accurate when identical copies of a word were presented bilaterally to both hemispheres, relative to unilateral single presentations. This bilateral advantage for words seems to be a robust effect in normals. The present study addressed the question of whether the bilateral advantage is restricted to lexical material or whether it is a more global phenomenon occurring for meaningful material in general. Thirty healthy participants performed a familiarity decision in which one copy of familiar and unfamiliar faces was presented tachistoscopically to the right visual hemifield (RVF), the left visual hemifield (LVF) or simultaneously to both visual hemifields (bilateral condition, BVF). We obtained a highly significant familiarity by visual field interaction(P < 0.006) showing that only for familiar faces, a bilateral advantage was obtained. Unfamiliar face processing did not yield a bilateral advantage. We conclude that interhemispheric cooperation only occurs for meaningful material for which cortical representations can be assumed.

Canonical views of faces and the cerebral hemispheres

Evidence is given for a special, canonical, status of one specific view in the identification of familiar faces. In the first experiment, subjects identified by name the fully frontal or profile poses of briefly familiarised individuals less efficiently than an intermediate pose. In addition, in a matching experiment using faces seen in different poses, it was found that one specific intermediate pose (corresponding to 22.5 degrees of angle from the full frontal view) was matched more efficiently in the right visual field (RVF) than in the left visual field (LVF). This finding supports the hypothesis of a superiority of the left hemisphere (LH) over the right hemisphere (RH) in processing a familiar face's canonical view. The other tested "noncanonical" views (i.e., full frontal, 45 degrees, and profile) of these same familiar faces were better matched in the LVF (i.e., the RH); especially at low levels of familiarity. We conclude that, for each familiar face, a viewer-centred representation of the canonical (22.5 degrees ) view is stored in the LH's memory system, whereas multiple views of familiar faces are stored in a memory system of the RH. With increasing levels of familiarity other views are increasingly more efficiently encoded by the LH, and in fact for facial self-recognition the full-front view is superior to any of the other tested views. These findings taken together suggest that complementary lateralised memory subsystems in the two cerebral hemispheres store different sets, only partially overlapping, of view-centred face representations.

Effects of talker variability on speechreading

The effects of talker variability on visual speech perception were tested by having subjects speechread sentences from either single-talker or mixed-talker sentence lists. Results revealed that changes in talker from trial to trial decreased speechreading performance. To help determine whether this decrement was due to talker change--and not a change in superficial characteristics of the stimuli--Experiment 2 tested speechreading from visual stimuli whose images were tinted by a single color, or mixed colors. Results revealed that the mixed-color lists did not inhibit speechreading performance relative to the single-color lists. These results are analogous to findings in the auditory speech literature and suggest that, like auditory speech, visual speech operations include a resource-demanding component that is influenced by talker variability.

False recognition of unfamiliar faces following right hemisphere damage: neuropsychological and anatomical observations

False recognition of unfamiliar faces was investigated in patients with focal right hemisphere damage (RHD) in order to define the neuropsychological and anatomical correlates of the recognition impairment and examine its relationship to prosopagnosia. Findings are discussed within the framework of the Bruce and Young (1986) model of face processing. Although false recognition and prosopagnosia were both present in some RHD patients, the two types of face recognition impairments were dissociable in others. Processing deficits in subjects with both false recognition and prosopagnosia were associated with posterior right hemisphere lesion sites and included severe face perception impairment and partial damage to face recognition units (FRUs). Prosopagnosia without false recognition was seen following near complete destruction of FRUs, but this type of dissociation could also occur when FRUs become disconnected. The opposite dissociation, false recognition without prosopagnosia, was observed following right prefrontal damage. We propose that false recognition in frontal patients results from the breakdown of strategic decision making and monitoring functions critical for determining whether a face is indeed that of a familiar person or whether there is merely a resemblance to a known individual. False recognition following prefrontal damage may also be related to confabulation, in which case familiarity or even specific identity are erroneously attributed to facial stimuli without the activation of an underlying memory representation.

Left and right hemifield advantages of fusions and combinations in audiovisual speech perception

If a place-of-articulation contrast is created between the auditory and the visual component syllables of videotaped speech, frequently the syllable that listeners report they have heard differs phonetically from the auditory component. These "McGurk effects", as they have come to be called, show that speech perception may involve some kind of intermodal process. There are two classes of these phenomena: fusions and combinations. Perception of the syllable /da/ when auditory /ba/ and visual /ga/ are presented provides a clear example of the former, and perception of the string /bga/ after presentation of auditory /ga/ and visual /ba/ an unambiguous instance of the latter. Besides perceptual fusions and combinations, hearing visually presented component syllables also shows an influence of vision on audition. It is argued that these "visual" responses arise from basically the same underlying processes that yield fusions and combinations, respectively. In the present study, the visual component of audiovisually incongruous CV-syllables was presented in the left and the right visual hemifield, respectively. Audiovisual fusion responses showed a left hemifield advantage, and audiovisual combination responses a right hemifield advantage. This finding suggests that the process of audiovisual integration differs between audiovisual fusions and combinations and, furthermore, that the two cerebral hemispheres contribute differentially to the two classes of response.

False recognition and misidentification of faces following right hemisphere damage

We report two patients who, following massive damage to the right hemisphere, showed a striking tendency for false recognition and misidentification of faces. Neuropsychological investigations revealed that excessive reliance on a feature-based left hemisphere strategy in face processing, combined with an inability to evaluate critically the output generated by the dysfunctional face recognition system, played a major role in the recognition errors and misidentifications. Our findings suggest that the feature based left hemisphere face recognition system is potentially error-prone, presumably because component facial features are likely to be shared among several different individuals, and that reliable recognition and identification of faces is critically dependent upon the efficient processing of configurational facial information by the right hemisphere. We propose further that decision making and monitoring functions relevant to the operations of the face recognition system are primarily lateralized to the right frontal lobe.

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.

Personal relevance and the human right hemisphere

Brain damage can selectively disrupt or distort information and ability across the range of human behaviors. One domain that has not been considered as an independent attribute consists of acquisition and maintenance of personal relevant entities such as "familiar" faces, persons, voices, names, linguistic expressions, handwriting, topography, and so on. In experimental studies of normal mentation, personal relevance is revealed in studies of emotion, arousal, affect, preference and familiarity judgments, and memory. Following focal brain damage, deficits and distortions in the experience of personal relevance, as well as in recognizing formerly personally relevant phenomena, are well known to occur. A review and interpretation of these data lead to a proposal that the right hemisphere has a special role in establishing, maintaining, and processing personally relevant aspects of the individual's world.

Understanding covert recognition

An implementation of Bruce and Young's (1986) functional model of face recognition is used to examine patterns of covert face recognition previously reported in a prosopagnosic patient, PH. Although PH is unable to recognize overly the faces of people known to him, he shows normal patterns of face processing when tested indirectly. A simple manipulation of one set of connections in the implemented model induces behaviour consistent with patterns of results from PH obtained in semantic priming and interference tasks. We compare this account with previous explanations of covert recognition and demonstrate that the implemented model provides the most natural and parsimonious account available. Two further patients are discussed who show deficits in person perception. The first (MS) is prosopagnosic but shows no covert recognition. The second (ME) is not prosopagnosic, but cannot access semantic information relating to familiar people. The model provides an account of recognition impairments which is sufficiently general also to be useful in describing these patients.

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.

Visual hemispace differences reflect hemisphere asymmetries

The relationship between the representation of the extracorporeal visual hemispace and the contralateral hemisphere has been investigated by presenting visual stimuli foveally either in the right or in the left hemispace. In a lexical decision task (Exp. 1) and a face-familiarity decision task (Exp. 2) lateral asymmetries very similar to those obtained using the divided visual field technique have been found. These results suggest that under particular circumstances the hemispace representation in the contralateral hemisphere overrides the retinal representation. Finally, it was found that in a lexical decision task performance with stimuli in the right hemispace was very similar to that with stimuli in a central position. The physiological and adaptive meaning of this phenomenon is discussed.

Access to identity-specific semantic codes from familiar faces

Information codes that can specify the surface form of a face are contrasted with semantic codes describing the properties of the person to whom the face belongs. Identity-specific semantic codes that specify characteristics of familiar people based on personal knowledge are in turn contrasted with the visually derived semantic codes and expression codes that can be derived even from unfamiliar faces. The idea that familiarity decisions (i.e., categorizing faces as belonging to known or unknown people) can be based on surface form, whereas certain types of semantic decision demand additional access to identity-specific semantic codes was investigated in four experiments. Experiments 1 and 3 showed that decisions based on identity-specific semantic codes (semantic decisions) usually take longer than decisions that do not demand access to an identity-specific semantic code (familiarity decisions). Experiment 2 showed that the use of familiar faces drawn from consistent or mixed categories affected reaction times for semantic decisions but not for familiarity decisions. Experiment 4 showed that semantic decisions to faces are taken more quickly (primed) when the faces have been recently seen, whereas there is no differential effect on semantic decisions to faces from previous semantic decisions involving the same people's names. These findings are consistent with the view that identity-specific semantic codes are accessed via face recognition units, and that outputs from face recognition units (which respond to the face's surface form) can be used as the basis for familiarity decisions.

Naming and categorizing faces and written names

In naming and categorization tasks, subjects were able to name aloud written names faster than photographs of faces, but were usually able to classify faces on familiarity (Experiment 1) or occupation (Experiments 2, 3 and 4) faster than written names. Faces were categorized faster than they were named, but written names were named faster than they could be categorized. Experiment 5 showed that familiar names were named more quickly than “rearranged” names made by exchanging the first and second names of familiar people.

This pattern of findings is consistent with the view that faces can only access name (phonological) codes via an intervening semantic representation, whereas written names can access semantic and name codes in parallel. In this respect, faces show properties similar to those of other visual objects, despite a priori reasons why this might not have been expected to be the case.