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See detailThe spatio-temporal correlates of holistic face perception
Schiltz, Christine UL; Jacques, Corentin; Rossion, Bruno

Poster (2007, May)

It is well known that faces are perceived holistically: their parts are integrated into a global or so-called holistic individual representation. Here we clarify where and how early in time individual ... [more ▼]

It is well known that faces are perceived holistically: their parts are integrated into a global or so-called holistic individual representation. Here we clarify where and how early in time individual holistic representations are extracted from the visual stimulus, by means of an event-related identity adaptation paradigm in fMRI (study 1; 10 subjects) and ERPs (study 2; 16 subjects). During blocks, subjects were presented with trials made of two sequentially presented faces and performed a same/different judgement on the top parts of each pair of faces. Face parts were presented either aligned or misaligned. For each face pair, the identity of top and bottom parts could be (a) both identical, (b) both different, (c) different only for the bottom part. The latter manipulation resulted in a strong face composite illusion behaviourally, i.e. the perception of identical top parts as being different, only in the aligned format. In the face-sensitive area of the middle fusiform gyrus (‘fusiform face area’) we observed a stronger response to the top part perceived as being different (release from adaptation), but only when the top and the bottom parts were aligned. It is consistent with the illusion of viewing different top parts of faces, and this release from fMR-adaptation is similar to the one observed in the ‘different’ condition for both aligned and misaligned parts. The same observations were made in ERPs as early as 150 ms, the amplitude of the electrophysiological response at occipito-temporal sites to the second face stimulus being reduced for identical relative to different top face parts, and to identical top parts perceived as different (aligned - bottom different). With both methods, the effects were stronger in the right hemisphere. Altogether, these observations indicate that individual faces are perceived holistically as early as 150 ms in the occipito-temporal cortex. [less ▲]

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See detailUnderstanding the functional neuroanatomy of acquired prosopagnosia
Sorger, Bettina; Goebel, Rainer; Schiltz, Christine UL et al

in NeuroImage (2007), 35(2), 836-852

One of the most remarkable disorders following brain damage is prosopagnosia, the inability to recognize faces. While a number of cases of prosopagnosia have been described at the behavioral level, the ... [more ▼]

One of the most remarkable disorders following brain damage is prosopagnosia, the inability to recognize faces. While a number of cases of prosopagnosia have been described at the behavioral level, the functional neuroanatomy of this face recognition impairment, and thus the brain regions critically involved in normal face recognition, has never been specified in great detail. Here, we used anatomical and functional magnetic resonance imaging (fMRI) to present the detailed functional neuroanatomy of a single case of acquired prosopagnosia (PS; Rossion, B., Caldara, R., Seghier, M., Schuller, A.-M., Lazeyras, F., Mayer, E., 2003a. A network of occipito-temporal face-sensitive areas besides the right middle fusiform gyrus is necessary for normal face processing. Brain 126, 2381-95; Rossion, B., Joyce, C.A., Cottrell, G.W., Tarr, M.J., 2003b. Early lateralization and orientation tuning for face, word, and object processing in the visual cortex. Neuroimage 20, 1609-24) with normal object recognition. First, we clarify the exact anatomical location and extent of PS' lesions in relation to (a) retinotopic cortex, (b) face-preferring regions, and (c) other classical visual regions. PS' main lesion - most likely causing her prosopagnosia - is localized in the posterior part of the right ventral occipitotemporal cortex. This lesion causes a left superior paracentral scotoma, as frequently observed in cases of prosopagnosia. While the borders of the early visual areas in the left hemisphere could be delineated well, the extensive posterior right-sided lesion hampered a full specification of the cortical representation of the left visual field. Using multiple scanning runs, face-preferring activation was detected within the right middle fusiform gyrus (MFG) in the so-called 'fusiform face area' ('FFA'), but also in the left inferior occipital gyrus (left 'OFA'), and in the right posterior superior temporal sulcus (STS). The dorsal part of the lateral occipital complex (LOC) and the human middle temporal cortex (hMT+/V5) were localized bilaterally. The color-preferring region V4/V8 was localized only in the left hemisphere. In the right hemisphere, the posterior lesion spared the ventral part of LOC, a region that may be critical for the preserved object recognition abilities of the patient, and the restriction of her deficit to the category of faces. The presumptive functions of both structurally damaged and preserved regions are discussed and new hypotheses regarding the impaired and preserved abilities of the patient during face and non-face object processing are derived. Fine-grained neurofunctional analyses of brain-damaged single cases with isolated recognition deficits may considerably improve our knowledge of the brain regions critically involved in specific visual functions, such as face recognition. [less ▲]

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See detailComputer assisted assessment of visuospatial working memory
Wantz, Marc UL; Martin, Romain UL; Hornung, Caroline UL et al

Poster (2007)

We present a new computer program that allows the assessment of visuospatial working memory (VSWM) in kindergarten children. The challenge for the assessment of VSWM in this age group is to present a test ... [more ▼]

We present a new computer program that allows the assessment of visuospatial working memory (VSWM) in kindergarten children. The challenge for the assessment of VSWM in this age group is to present a test design that is easily understandable for children and thus not too difficult while at the same time implying additional processing elements above the pure storage of positional information (according to the definition of Engle et al. 1999 that working memory combines an element of pure storage with processes of executive attention) The adopted test paradigm is based on a grid / no-grid paradigm for which a previous fMRI study with an adult population has shown that the memorization of positional information in a perceptively undifferentiated space (no-grid condition) requires additional attentional processes compared to the memorization of positional information in a perceptively structured space (grid condition). The setting of the test was adapted to children in Kindergarten. We used a tablet PC to administer the test. This procedure excludes that children fail because they can’t use the computer mouse in an appropriate way. The different items show a 4x4 grid where the eyes of a manikin appear on a dark background. Children are told that the positions of different manikins in a dark room have to be memorized. After a short period of time the eyes disappear again and up to four positions have to be memorized in this way. The test person then clicks in the grid where he believes that the different manikins are hidden. The setting allows measuring performance in terms of accuracy and time. First results with kindergarten children in Luxemburg will be presented showing the correlation of this VSWM task with other visuospatial and numerical tasks. [less ▲]

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See detailVisuelle Wahrnehmung und arithmetische Kompetenzen
Wantz, Marc UL; Martin, Romain UL; Schiltz, Christine UL

in Motorik (2007), 4

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See detailNumerical competencies of young children
Wantz, Marc UL; Martin, Romain UL; Schiltz, Christine UL

Scientific Conference (2007)

Numerous studies show that wide ranges of competencies in different fields are necessary to develop a good numerical competency. Our research tried to find an answer to the question, which out of various ... [more ▼]

Numerous studies show that wide ranges of competencies in different fields are necessary to develop a good numerical competency. Our research tried to find an answer to the question, which out of various factors mainly influence the numerical competencies of young children. We focused on visuospatial, perceptive and tactile skills as determinants of the quality of early numerical representations. We adopted a longitudinal research design with three periods of data collection (two data collections during the second year of kindergarten and one at the end of first grade). Our test setting for the kindergarten included tests in the three areas mentioned above. The evaluation of these results shows that the numerical competencies are influenced by visuospatial competencies and knowledge of pre-numerical facts. An importance of the perceptive and tactile skills could not be established. At the end of first grade, after formal mathematical instruction, we made a mathematical competency test. A structural equation model of the subtests shows that the numerical knowledge at this stage can be divided in two separate factors: 1. A representational numerical factor (analogical representation of quantities: Triple Code model of Dehaene) 2. A more formal knowledge of mathematics (visual Arabic representation: Triple Code model of Dehaene, 1992). Predicting these two factors from the competency profile measured in kindergarten showed that the representational numerical factor was very well predicted from a general spatio-numerical factor found in the previous year, while the formal knowledge was predicted to a lesser degree by tactile skills measured at the end of kindergarten. Implications for numerical teaching in Kindergarten will be discussed. [less ▲]

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See detailFaces are represented holistically in the human occipito-temporal cortex
Schiltz, Christine UL; Rossion, Bruno

in NeuroImage (2006), 32(3), 1385-1394

Two identical top parts of a face photograph look different if their bottom parts differ. This perceptual illusion, the "face composite effect", is taken as strong evidence that faces are processed as a ... [more ▼]

Two identical top parts of a face photograph look different if their bottom parts differ. This perceptual illusion, the "face composite effect", is taken as strong evidence that faces are processed as a whole rather than as a collection of independent features. To test the hypothesis that areas responding preferentially to faces in the human brain represent faces holistically, we recorded functional magnetic resonance imaging (fMRI) during an adaptation paradigm with the composite face illusion. In both the middle fusiform gyrus (MFG) and the inferior occipital gyrus (IOG), we observed a significantly larger response to the same top face when it was aligned with different bottom parts than with the same bottom part, with a most robust effect in the right middle fusiform gyrus. This difference was not found when the top and the bottom face parts were spatially misaligned or when the faces were presented upside-down. These findings indicate that facial features are integrated into holistic face representations in areas of the human visual cortex responding preferentially to faces. [less ▲]

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See detailPreserved individual face discrimination in the ventral lateral occipital complex (vloc) of a brain-damaged prosopagnosic patient
Dricot, L; Schiltz, Christine UL; Sorger, B et al

Scientific Conference (2006, June 17)

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See detailImpaired face discrimination in acquired prosopagnosia is associated with abnormal response to individual faces in the right middle fusiform gyrus
Schiltz, Christine UL; Sorger, Bettina; Caldara, Roberto et al

in Cerebral Cortex (2006), 16(4), 574-586

The middle fusiform gyrus (MFG) and the inferior occipital gyrus (IOG) are activated by both detection and identification of faces. Paradoxically, patients with acquired prosopagnosia following lesions to ... [more ▼]

The middle fusiform gyrus (MFG) and the inferior occipital gyrus (IOG) are activated by both detection and identification of faces. Paradoxically, patients with acquired prosopagnosia following lesions to either of these regions in the right hemisphere cannot identify faces, but can still detect faces. Here we acquired functional magnetic resonance imaging (fMRI) data during face processing in a patient presenting a specific deficit in individual face recognition, following lesions encompassing the right IOG. Using an adaptation paradigm we show that the fMRI signal in the rMFG of the patient, while being larger in response to faces as compared to objects, does not differ between conditions presenting identical and distinct faces, in contrast to the larger response to distinct faces observed in controls. These results suggest that individual discrimination of faces critically depends on the integrity of both the rMFG and the rIOG, which may interact through re-entrant cortical connections in the normal brain. [less ▲]

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See detailRecovery from adaptation to facial identity is larger for upright than inverted faces in the human occipito-temporal cortex
Mazard, Angelique; Schiltz, Christine UL; Rossion, Bruno

in Neuropsychologia (2006), 44(6), 912-922

Human faces look more similar to each other when they are presented upside-down, leading to an increase of error rates and response times during individual face discrimination tasks. Here we used ... [more ▼]

Human faces look more similar to each other when they are presented upside-down, leading to an increase of error rates and response times during individual face discrimination tasks. Here we used functional magnetic resonance imaging (fMRI) to test the hypothesis that this perceived similarity leads to a lower recovery from identity adaptation for inverted faces than for upright faces in face-sensitive areas of the occipito-temporal cortex. Ten subjects were presented with blocks of upright and inverted faces, with the same face identity repeated consecutively in half of the blocks, and different facial identities repeated in the other blocks. When face stimuli were presented upright, the percent signal change in the bilateral middle fusiform gyrus (MFG) was larger for different faces as compared to same faces, replicating previous observations of a recovery from facial identity adaptation in this region. However, there was no significant recovery from adaptation when different inverted faces were presented. Most interestingly, the difference in activation between upright and inverted faces increased progressively during a block when different facial identities were presented. A similar pattern of activation was found in the left middle fusiform gyrus, but was less clear-cut in bilateral face-sensitive areas of the inferior occipital cortex. These findings show that the differential level of activation to upright and inverted faces in the fusiform gyrus is mainly due to a difference in recovery from adaptation, and they explain the discrepancies in the results reported in previous fMRI studies which compared the processing of upright and inverted faces. The lack of recovery from adaptation for inverted faces in the fusiform gyrus may underlie the face inversion effect (FIE), which takes place during perceptual encoding of individual face representations. [less ▲]

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See detailFaces are processed holistically in the right middle fusiform gyrus
Schiltz, Christine UL; Rossion, Bruno

Scientific Conference (2005, May)

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See detailFace-sensitive responses in the occipital inferior cortex of normal humans through feedback inputs from the fusiform gyrus? Evidence from neuroimaging studies of brain-damaged prosopagnosic patient
Rossion, Bruno; Sorger, Bettina; Schiltz, Christine UL et al

Poster (2004, August 13)

In humans, neuroimaging studies have identified two major visual extrastriate areas presenting face-sensitive responses: in the inferior occipital cortex (‘occipital face area’, OFA), and the middle ... [more ▼]

In humans, neuroimaging studies have identified two major visual extrastriate areas presenting face-sensitive responses: in the inferior occipital cortex (‘occipital face area’, OFA), and the middle fusiform gyrus (the ‘fusiform face area’, FFA), with a right hemispheric dominance. It has been proposed that the OFA, located anteriorly to foveal V4v (Halgren et al., 1999), has a critical role in the early perception of facial features and provides the feedforward outputs to later stages of face processing in both the FFA and the STS (Haxby et al., 2000). However, we have recently reported a normal activation of the right FFA despite a lesion encompassing the region of the right OFA in a brain-damaged prosopagnosic patient, PS (Rossion et al., 2003), suggesting that the face-sensitive responses observed at the level of the OFA in normals may rather arise from feedback connections from the FFA. Here we provide complementary fMRI evidence supporting this view. First, the normal differential activation for faces and objects in the right FFA of PS was observed only for left visual field presentations and is thus unlikely to originate from contralateral intact regions of the occipital cortex (e.g. left OFA). Second, the time-course in the right FFA and left OFA of PS for centrally presented items suggests an earlier differential activity between faces and objects in the most anterior region, the FFA. Finally, we imaged another (prosop)agnosic patient (NS, Delvenne et al., 2004) with a lesion encompassing the right FFA but sparing all posterior visual areas, and failed to disclose any face-sensitive response in his nonetheless structurally and functionnally intact occipital cortex. Together, these findings illustrate the necessary role of both the right FFA and OFA for accurate face perception, and reinforce the hypothesis that a dominant (feedback) connection from the FFA to the OFA subtends face-sensitive responses observed in the latter area when processing faces. [less ▲]

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See detailFace-sensitive responses in the occipital inferior cortex of normal humans through feedback inputs from the fusiform gyrus ?: Evidence from neuroimaging studies of brain-damaged prosopagnosic patients
Schiltz, Christine UL; Caldara, Roberto; Sorger, Bettina et al

Poster (2004, June)

In humans, neuroimaging studies have identified two major visual extrastriate areas presenting face-sensitive responses: in the inferior occipital cortex (‘occipital face area’, OFA), and the middle ... [more ▼]

In humans, neuroimaging studies have identified two major visual extrastriate areas presenting face-sensitive responses: in the inferior occipital cortex (‘occipital face area’, OFA), and the middle fusiform gyrus (the ‘fusiform face area’, FFA), with a right hemispheric dominance. It has been proposed that the OFA, located anteriorly to foveal V4v (Halgren et al., 1999), has a critical role in the early perception of facial features and provides the feedforward outputs to later stages of face processing in both the FFA and the STS (Haxby et al., 2000). However, we have recently reported a normal activation of the right FFA despite a lesion encompassing the region of the right OFA in a brain-damaged prosopagnosic patient, PS (Rossion et al., 2003), suggesting that the face-sensitive responses observed at the level of the OFA in normals may rather arise from feedback connections from the FFA. Here we provide complementary fMRI evidence supporting this view. First, the normal differential activation for faces and objects in the right FFA of PS was observed only for left visual field presentations and is thus unlikely to originate from contralateral intact regions of the occipital cortex (e.g. left OFA). Second, the time-course in the right FFA and left OFA of PS for centrally presented items suggests an earlier differential activity between faces and objects in the most anterior region, the FFA. Finally, we imaged another (prosop)agnosic patient (NS, Delvenne et al., 2004) with a lesion encompassing the right FFA but sparing all posterior visual areas, and failed to disclose any face-sensitive response in his nonetheless structurally and functionnally intact occipital cortex. Together, these findings illustrate the necessary role of both the right FFA and OFA for accurate face perception, and reinforce the hypothesis that a dominant (feedback) connection from the FFA to the OFA subtends face-sensitive responses observed in the latter area when processing faces. [less ▲]

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See detailThe functionally defined right occipital and fusiform "face areas" discriminate novel from visually familiar faces
Rossion, Bruno; Schiltz, Christine UL; Crommelinck, Marc

in NeuroImage (2003), 19(3), 877-883

Neuroimaging (PET and fMRI) studies have identified a set of brain areas responding more to faces than to other object categories in the visual extrastriate cortex of humans. This network includes the ... [more ▼]

Neuroimaging (PET and fMRI) studies have identified a set of brain areas responding more to faces than to other object categories in the visual extrastriate cortex of humans. This network includes the middle lateral fusiform gyrus (the fusiform face area, or FFA) as well as the inferior occipital gyrus (occipital face area, OFA). The exact functions of these areas in face processing remain unclear although it has been argued that their primary function is to distinguish faces from nonface object categories-"face detection"-or also to discriminate among faces, irrespective of their visual familiarity to the observer. Here, we combined the data from two previous positron emission tomography (PET) studies to show that the functionally defined face areas are involved in the automatic discrimination between unfamiliar faces and familiar faces. Consistent with previous studies, a face localizer contrast (faces-objects) revealed bilateral activation in the middle lateral fusiform gyrus (FFA, BA37) and in the right inferior occipital cortex (OFA, BA19). Within all the regions of the right hemisphere, larger levels of activation were found for unfamiliar as compared to familiar faces. These results suggest that the very same areas involved in categorizing faces at the basic or individual level, play a role in differentiating familiar faces from new faces, showing an overlap between visual and presemantic mnesic representations of faces in the right hemisphere. [less ▲]

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See detailHow does the brain discriminate familiar and unfamiliar faces? A pet study of face categorical perception
Rossion, Bruno; Schiltz, Christine UL; Robaye, Laurence et al

in Journal of Cognitive Neuroscience (2001), 13(7), 1019-1034

Where and how does the brain discriminate familiar and unfamiliar faces? This question has not been answered yet by neuroimaging studies partly because different tasks were performed on familiar and ... [more ▼]

Where and how does the brain discriminate familiar and unfamiliar faces? This question has not been answered yet by neuroimaging studies partly because different tasks were performed on familiar and unfamiliar faces, or because familiar faces were associated with semantic and lexical information. Here eight subjects were trained during 3 days with a set of 30 faces. The familiarized faces were morphed with unfamiliar faces. Presented with continua of unfamiliar and familiar faces in a pilot experiment, a group of eight subjects presented a categorical perception of face familiarity: there was a sharp boundary in percentage of familiarity decisions between 40% and 60% faces. In the main experiment, subjects were scanned (PET) on the fourth day (after 3 days of training) in six conditions, all requiring a sex classification task. Completely novel faces (0%) were presented in Condition 1 and familiar faces (100%) in Condition 6, while faces of steps of 20% in the continuum of familiarity were presented in Conditions 2 to 5 (20% to 80%). A principal component analysis (PCA) indicated that most variations in neural responses were related to the dissociation between faces perceived as familiar (60% to 100%) and faces perceived as unfamiliar (0 to 40%). Subtraction analyses did not disclose any increase of activation for faces perceived as familiar while there were large relative increases for faces perceived as unfamiliar in several regions of the right occipito-temporal visual pathway. These changes were all categorical and were observed mainly in the right middle occipital gyrus, the right posterior fusiform gyrus, and the right inferotemporal cortex. These results show that (1) the discrimination between familiar and unfamiliar faces is related to relative increases in the right ventral pathway to unfamiliar/novel faces; (2) familiar and unfamiliar faces are discriminated in an all-or-none fashion rather than proportionally to their resemblance to stored representations; and (3) categorical perception of faces is associated with abrupt changes of brain activity in the regions that discriminate the two extremes of the multidimensional continuum. [less ▲]

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See detailA pet study of human skill learning: Changes in brain activity related to learning an orientation discrimination task
Schiltz, Christine UL; Bodart, Jean-Michel; Michel, Christian et al

in Cortex: A Journal Devoted to the Study of the Nervous System and Behavior (2001), 37(2), 243-265

Using 15O-water 3D positron emission tomography we investigated the effect of training in orientation discrimination upon cerebral activity in healthy human adults. When subjects are trained in this ... [more ▼]

Using 15O-water 3D positron emission tomography we investigated the effect of training in orientation discrimination upon cerebral activity in healthy human adults. When subjects are trained in this discrimination task, they learn the visuo-motor stimulus-response association required by the task and they increase their perceptual abilities in orientation discrimination. The present study was designed to investigate the rCBF modifications related to both these learning processes induced by training in orientation discrimination. PET data were acquired on two separate days (before and after training). Comparing the activation pattern related to orientation discrimination before and after the training period we observed activity decreases located in the left cerebellar cortex, in the right precentral gyrus and bilaterally in the fusiform gyri. The only region showing an activity increase was located in the body of the right caudate nucleus. These findings confirm the role of the neostriatum in skill learning and highlight the importance of mechanisms resulting in cortical and cerebellar neuronal activity decreases in this type of learning. [less ▲]

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See detailThe neural basis of human face categorization: A parametric pet study
Rossion, B; Schiltz, Christine UL; Robaye, L et al

Poster (1999, June)

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