Implicit face perception in a patient with visual agnosia? Evidence from behavioural and eye-tracking analyses

Eye-movement strategies in developmental prosopagnosia and "super" face recognition

Developmental prosopagnosia (DP) is a cognitive condition characterized by a severe deficit in face recognition. Few investigations have examined whether impairments at the early stages of processing may underpin the condition, and it is also unknown whether DP is simply the "bottom end" of the typical face-processing spectrum. To address these issues, we monitored the eye-movements of DPs, typical perceivers, and "super recognizers" (SRs) while they viewed a set of static images displaying people engaged in naturalistic social scenarios. Three key findings emerged: (a) Individuals with more severe prosopagnosia spent less time examining the internal facial region, (b) as observed in acquired prosopagnosia, some DPs spent less time examining the eyes and more time examining the mouth than controls, and (c) SRs spent more time examining the nose-a measure that also correlated with face recognition ability in controls. These findings support previous suggestions that DP is a heterogeneous condition, but suggest that at least the most severe cases represent a group of individuals that qualitatively differ from the typical population. While SRs seem to merely be those at the "top end" of normal, this work identifies the nose as a critical region for successful face recognition.

The pupillary response discriminates between subjective and objective familiarity and novelty

The pupil response discriminates between old and new stimuli, with old stimuli characterized by larger pupil dilation patterns than new stimuli. We sought to explore the cause of the pupil old/new effect and discount the effect of targetness, effort, recollection retrieval, and complexity of the recognition decision. Two experiments are reported in which the pupil response and the eye fixation patterns were measured, while participants identified novel and familiar object stimuli, in two separate tasks, emphasizing either novelty or familiarity detection. In Experiment 1, familiarity and novelty decisions were taken using a rating scale, while in Experiment 2 a simpler yes/no decision was used. In both experiments, we found that detection of target familiar stimuli resulted in greater pupil dilation than the detection of target novel stimuli, while the duration of the first fixation discriminated between familiar and novel stimuli as early as within 320 ms after stimulus onset. Importantly, the pupil response distinguished between the objective (during an earlier temporal component) and the subjective (during a later temporal component) status of the stimulus for misses and false alarms. In the light of previous findings, we suggest that the pupil and fixation old/new effects reflect the distinct neural and cognitive mechanisms involved in the familiarity and novelty decisions. The findings also have important implications for the use of pupil dilation and eye movement patterns to explore explicit and implicit memory processes.

Superior voice recognition in a patient with acquired prosopagnosia and object agnosia

Anecdotally, it has been reported that individuals with acquired prosopagnosia compensate for their inability to recognize faces by using other person identity cues such as hair, gait or the voice. Are they therefore superior at the use of non-face cues, specifically voices, to person identity? Here, we empirically measure person and object identity recognition in a patient with acquired prosopagnosia and object agnosia. We quantify person identity (face and voice) and object identity (car and horn) recognition for visual, auditory, and bimodal (visual and auditory) stimuli. The patient is unable to recognize faces or cars, consistent with his prosopagnosia and object agnosia, respectively. He is perfectly able to recognize people's voices and car horns and bimodal stimuli. These data show a reverse shift in the typical weighting of visual over auditory information for audiovisual stimuli in a compromised visual recognition system. Moreover, the patient shows selectively superior voice recognition compared to the controls revealing that two different stimulus domains, persons and objects, may not be equally affected by sensory adaptation effects. This also implies that person and object identity recognition are processed in separate pathways. These data demonstrate that an individual with acquired prosopagnosia and object agnosia can compensate for the visual impairment and become quite skilled at using spared aspects of sensory processing. In the case of acquired prosopagnosia it is advantageous to develop a superior use of voices for person identity recognition in everyday life.

Training of familiar face recognition and visual scan paths for faces in a child with congenital prosopagnosia

In the current report we describe a successful training study aimed at improving recognition of a set of familiar face photographs in K., a 4-year-old girl with congenital prosopagnosia (CP). A detailed assessment of K.'s face-processing skills showed a deficit in structural encoding, most pronounced in the processing of facial features within the face. In addition, eye movement recordings revealed that K.'s scan paths for faces were characterized by a large percentage of fixations directed to areas outside the internal core features (i.e., eyes, nose, and mouth), in particular by poor attendance to the eye region. Following multiple baseline assessments, training focused on teaching K. to reliably recognize a set of familiar face photographs by directing visual attention to specific characteristics of the internal features of each face. The training significantly improved K.'s ability to recognize the target faces, with her performance being flawless immediately after training as well as at a follow-up assessment 1 month later. In addition, eye movement recordings following training showed a significant change in K.'s scan paths, with a significant increase in the percentage of fixations directed to the internal features, particularly the eye region. Encouragingly, not only was the change in scan paths observed for the set of familiar trained faces, but it generalized to a set of faces that was not presented during training. In addition to documenting significant training effects, our study raises the intriguing question of whether abnormal scan paths for faces may be a common factor underlying face recognition impairments in childhood CP, an issue that has not been explored so far.

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.

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.

The Eyes Remember It: Oculography and Pupillometry during Recollection in Three Amnesic Patients

Two patients (TC and SS) with lesions that included the hippocampal regions (predominantly on the left side) were severely impaired in their recall of simple, verbally stated facts. However, both patients remembered spatial information that was temporally associated with semantic information. Specifically, TC and SS could not recall explicitly the content of an episode, but their spontaneous oculomotor behavior showed that they retained some information about the event as their gaze automatically returned to the locations on the computer screen where visual information had been paired to verbally presented information. Thus, this spatial information is implicit, automatically retrieved, and eye-based, as when one patient (TC) was asked to point with the finger to the same positions he was impaired. In addition, in an old/new recognition task, TC and SS and an additional patient, OB, showed significant changes in eye pupil diameter when viewing novel visual stimuli compared to stimuli that they had previously seen, also when they (incorrectly) declared with confidence that an old item was new. The spared memory of these patients, despite severe amnesia for the learning episodes, is characterized by a re-enactment of previous eye fixations that were associated with each (forgotten) episode and physiological responses (as indexed by pupillometry) to previously seen stimuli. Such spared memory can be seen as a type of “snapshot” memory, which automatically processes eye-based spatial information and whose content remains implicit. Finally, we surmise on the basis of the neuroanatomical findings of these patients, that neural substrates in the spared (right) hemisphere might support both the eye fixations' re-enactment and implicit visual pattern recognition.

Processing of normal, inverted, and scrambled faces in a patient with prosopagnosia: behavioural and eye tracking data

In this study, we addressed the issue of a spared processing of faces in a patient (SB) with severe prosopagnosia. We designed an experiment comprising of two parts. In Part I, normal upright faces were entwined with scrambled faces, while in Part II normal upright faces were mixed with inverted faces, under unlimited time exposure. Performance, decision times, and eye movements were measured in both parts. The results indicated that SB categorised the normal faces better in the context of inverted faces than in the context of scrambled faces. Furthermore, SB's performance was better for the inverted faces than for the scrambled faces. Overall, SB performed better on the abnormal faces than on the normal faces, as did the control participants. Eye-tracking data showed that the pattern observed for the number of fixations and for exploration order was similar in SB and in controls. In the discussion, we propose that, despite his severe prosopagnosia, SB might have retained some kind of processing specific to face perception. Further investigations will be required, using limited time exposure, to determine the nature of this spared processing.