Raika Pancaroglu

The anatomic basis of the right face-selective N170 IN acquired prosopagnosia: A combined ERP/fMRI study

The N170 waveform is larger over posterior temporal cortex when healthy subjects view faces than when they view other objects. Source analyses have produced mixed results regarding whether this effect originates in the fusiform face area (FFA), lateral occipital cortex, or superior temporal sulcus (STS), components of the core face network. In a complementary approach, we assessed the face-selectivity of the right N170 in five patients with acquired prosopagnosia, who also underwent structural and functional magnetic resonance imaging. We used a non-parametric bootstrap procedure to perform single-subject analyses, which reliably confirmed N170 face-selectivity in each of 10 control subjects. Anterior temporal lesions that spared the core face network did not affect the face-selectivity of the N170. A face-selective N170 was also present in another subject who had lost only the right FFA. However, face-selectivity was absent in two patients with lesions that eliminated the occipital face area (OFA) and FFA, sparing only the STS. Thus while the right FFA is not necessary for the face-selectivity of the N170, neither is the STS sufficient. We conclude that the face-selective N170 in prosopagnosia requires residual function of at least two components of the core face-processing network.

Voice Recognition in Face-Blind Patients.

Right or bilateral anterior temporal damage can impair face recognition, but whether this is an associative variant of prosopagnosia or part of a multimodal disorder of person recognition is an unsettled question, with implications for cognitive and neuroanatomic models of person recognition. We assessed voice perception and short-term recognition of recently heard voices in 10 subjects with impaired face recognition acquired after cerebral lesions. All 4 subjects with apperceptive prosopagnosia due to lesions limited to fusiform cortex had intact voice discrimination and recognition. One subject with bilateral fusiform and anterior temporal lesions had a combined apperceptive prosopagnosia and apperceptive phonagnosia, the first such described case. Deficits indicating a multimodal syndrome of person recognition were found only in 2 subjects with bilateral anterior temporal lesions. All 3 subjects with right anterior temporal lesions had normal voice perception and recognition, 2 of whom performed normally on perceptual discrimination of faces. This confirms that such lesions can cause a modality-specific associative prosopagnosia.

Word and text processing in acquired prosopagnosia.

A novel hypothesis of object recognition asserts that multiple regions are engaged in processing an object type, and that cerebral regions participate in processing multiple types of objects. In particular, for high‐level expert processing, it proposes shared rather than dedicated resources for word and face perception, and predicts that prosopagnosic subjects would have minor deficits in visual word processing, and alexic subjects would have subtle impairments in face perception. In this study, we evaluated whether prosopagnosic subjects had deficits in processing either the word content or the style of visual text.

Getting lost: Topographic skills in acquired and developmental prosopagnosia

Previous studies report that acquired prosopagnosia is frequently associated with topographic disorientation. Whether this is associated with a specific anatomic subtype of prosopagnosia, how frequently it is seen with the developmental variant, and what specific topographic function is impaired to account for this problem are not known. We studied ten subjects with acquired prosopagnosia from either occipitotemporal or anterior temporal (AT) lesions and seven with developmental prosopagnosia. Subjects were given a battery of topographic tests, including house and scene recognition, the road map test, a test of cognitive map formation, and a standardized self-report questionnaire. House and/or scene recognition were frequently impaired after either occipitotemporal or AT lesions in acquired prosopagnosia. Subjects with occipitotemporal lesions were also impaired in cognitive map formation: an overlap analysis identified right fusiform and parahippocampal gyri as a likely correlate. Only one subject with acquired prosopagnosia had mild difficulty with directional orientation on the road map test. Only one subject with developmental prosopagnosia had difficulty with cognitive map formation, and none were impaired on the other tests. Scores for house and scene recognition correlated most strongly with the results of the questionnaire. We conclude that topographic disorientation in acquired prosopagnosia reflects impaired place recognition, with a contribution from poor cognitive map formation when there is occipitotemporal damage. Topographic impairments are less frequent in developmental prosopagnosia.

Neuroanatomic correlates of the feature-salience hierarchy in face processing: An fMRI -adaptation study

Previous fMRI studies suggest that faces are represented holistically in human face processing regions. On the other hand, behavioral studies have also shown that some facial features are more salient than others for face recognition: the neural basis of this feature-salience hierarchy is not known. We used fMRI-adaptation together with a behavioral discrimination task and an ideal observer analysis to ask (1) whether different face parts contribute different amounts to the neural signal in face responsive regions, and (2) whether this response correlates more with the behavioral performance of human subjects or with the physical properties of the face stimuli. Twenty-three subjects performed a same/different discrimination experiment to characterize their ability to detect changes to different face parts. The same subjects underwent an fMRI-adaptation study, in which limited portions of the faces were repeated or changed between alternating stimuli. The behavioral study showed high efficiency in identity discrimination when the whole face, top half, or eyes changed, and low efficiency when the bottom half, nose, or mouth changed. During fMRI, there was a release of adaptation in the right and left fusiform face area (FFA) with changes to the whole face, top face-half, or the eyes. Changes to the bottom half, nose or mouth did not result in a significant release of adaptation in the right FFA, although bottom-half changes resulted in a release of adaptation in the left FFA. Adaptation in the right and left FFA and the right pSTS was correlated with human perceptual efficiency but not with ideal observer measures of the physical image differences between face parts. The feature-salience hierarchy of human face perception is therefore reflected in the activity in the right and left FFA and right pSTS, further supporting the key role of these structures in our perceptual experience of faces.

Seeing the eyes in acquired prosopagnosia.

Case reports have suggested that perception of the eye region may be impaired more than that of other facial regions in acquired prosopagnosia. However, it is unclear how frequently this occurs, whether such impairments are specific to a certain anatomic subtype of prosopagnosia, and whether these impairments are related to changes in the scanning of faces. We studied a large cohort of 11 subjects with this rare disorder, who had a variety of occipitotemporal or anterior temporal lesions, both unilateral and bilateral. Lesions were characterized by functional and structural imaging. Subjects performed a perceptual discrimination test in which they had to discriminate changes in feature position, shape, or external contour. Test conditions were manipulated to stress focused or divided attention across the whole face. In a second experiment we recorded eye movements while subjects performed a face memory task. We found that greater impairment for eye processing was more typical of subjects with occipitotemporal lesions than those with anterior temporal lesions. This eye selectivity was evident for both eye position and shape, with no evidence of an upper/lower difference for external contour. A greater impairment for eye processing was more apparent under attentionally more demanding conditions. Despite these perceptual deficits, most subjects showed a normal tendency to scan the eyes more than the mouth. We conclude that occipitotemporal lesions are associated with a partially selective processing loss for eye information and that this deficit may be linked to loss of the right fusiform face area, which has been shown to have activity patterns that emphasize the eye region.

The right anterior temporal lobe variant of prosopagnosia

grant RES 061-23-0040, and JB by CIHR grant MOP-102567, and Canada Research Chair program. The right anterior temporal lobe variant of prosopagnosia Raika Pancaroglu1, Thomas Busigny1, Samantha Johnston1, Alla Sekunova1, Bradley Duchaine2, Jason JS Barton1 1Departments of Ophthalmology and Visual Sciences, Medicine, and Psychology, University of British Columbia, Vancouver, Canada 2Department of Psychological and Brain Sciences, Dartmouth College, Hanover, New Hampshire, USA

Perceptual learning of faces: A rehabilitative study of acquired prosopagnosia

Despite many studies of acquired prosopagnosia, there have been only a few attempts at its rehabilitation, all in single cases, with a variety of mnemonic or perceptual approaches, and of variable efficacy. In a cohort with acquired prosopagnosia, we evaluated a perceptual learning program that incorporated variations in view and expression, which was aimed at training perceptual stages of face processing with an emphasis on ecological validity. Ten patients undertook an 11-week face training program and an 11-week control task. Training required shape discrimination between morphed facial images, whose similarity was manipulated by a staircase procedure to keep training near a perceptual threshold. Training progressed from blocks of neutral faces in frontal view through increasing variations in view and expression. Whereas the control task did not change perception, training improved perceptual sensitivity for the trained faces and generalized to new untrained expressions and views of those faces. There was also a significant transfer to new faces. Benefits were maintained over a 3-month period. Training efficacy was greater for those with more perceptual deficits at baseline. We conclude that perceptual learning can lead to persistent improvements in face discrimination in acquired prosopagnosia. This reflects both acquisition of new skills that can be applied to new faces as well as a degree of overlearning of the stimulus set at the level of 3-D expression-invariant representations.

The relationship between visual word and face processing lateralization in the fusiform gyri: A cross-sectional study.

Visual words and faces activate similar networks but with complementary hemispheric asymmetries, faces being lateralized to the right and words to the left. A recent theory proposes that this reflects developmental competition between visual word and face processing. We investigated whether this results in an inverse correlation between the degree of lateralization of visual word and face activation in the fusiform gyri. 26 literate right-handed healthy adults underwent functional MRI with face and word localizers. We derived lateralization indices for cluster size and peak responses for word and face activity in left and right fusiform gyri, and correlated these across subjects. A secondary analysis examined all face- and word-selective voxels in the inferior occipitotemporal cortex. No negative correlations were found. There were positive correlations for the peak MR response between word and face activity within the left hemisphere, and between word activity in the left visual word form area and face activity in the right fusiform face area. The face lateralization index was positively rather than negatively correlated with the word index. In summary, we do not find a complementary relationship between visual word and face lateralization across subjects. The significance of the positive correlations is unclear: some may reflect the influences of general factors such as attention, but others may point to other factors that influence lateralization of function.

Temporal dynamics of the face familiarity effect: bootstrap analysis of single-subject event-related potential data.

Prior event-related potential studies using group statistics within a priori selected time windows have yielded conflicting results about familiarity effects in face processing. Our goal was to evaluate the temporal dynamics of the familiarity effect at all time points at the single-subject level. Ten subjects were shown faces of anonymous people or celebrities. Individual results were analysed using a point-by-point bootstrap analysis. While familiarity effects were less consistent at later epochs, all subjects showed them between 130 and 195 ms in occipitotemporal electrodes. However, the relation between the time course of familiarity effects and the peak latency of the N170 was variable. We concluded that familiarity effects between 130 and 195 ms are robust and can be shown in single subjects. The variability of their relation to the timing of the N170 potential may lead to underestimation of familiarity effects in studies that use group-based statistics.