Canonical representations of fingers and dots trigger an automatic activation of number semantics: an EEG study on 10-year-old children

in Neuropsychologia (2021)

Over the course of development, children must learn to map a non-symbolic representation of magnitude to a more precise symbolic system. There is solid evidence that finger and dot representations can ... [more ▼]

Over the course of development, children must learn to map a non-symbolic representation of magnitude to a more precise symbolic system. There is solid evidence that finger and dot representations can facilitate or even predict the acquisition of this mapping skill. While several behavioral studies demonstrated that canonical representations of fingers and dots automatically activate number semantics, no study so far has investigated their cerebral basis. To examine these questions, 10-year-old children were presented a behavioral naming task and a Fast Periodic Visual Stimulation EEG paradigm. In the behavioral task, children had to name as fast and as accurately as possible the numbers of dots and fingers presented in canonical and non-canonical configurations. In the EEG experiment, one category of stimuli (e.g., canonical representation of fingers or dots) was periodically inserted (1/5) in streams of another category (e.g., non-canonical representation of fingers or dots) presented at a fast rate (4 Hz). Results demonstrated an automatic access to number semantics and bilateral categorical responses at 4 Hz/5 for canonical representations of fingers and dots. Some differences between finger and dot configuration’s processing were nevertheless observed and are discussed in light of an effortful-automatic continuum hypothesis. [less ▲]

Dissociated face- and word-selective intracerebral responses in the human ventral occipito-temporal cortex.

in Brain Structure & Function (2021), 226(9), 3031-49

The extent to which faces and written words share neural circuitry in the human brain is actively debated. Here, we compare face-selective and word-selective responses in a large group of patients (N = 37 ... [more ▼]

The extent to which faces and written words share neural circuitry in the human brain is actively debated. Here, we compare face-selective and word-selective responses in a large group of patients (N = 37) implanted with intracerebral electrodes in the ventral occipito-temporal cortex (VOTC). Both face-selective (i.e., significantly different responses to faces vs. non-face visual objects) and word-selective (i.e., significantly different responses to words vs. pseudofonts) neural activity is isolated with frequency-tagging. Critically, this sensitive approach allows to objectively quantify category-selective neural responses and disentangle them from general visual responses. About 70% of significant electrode contacts show either face-selectivity or word-selectivity only, with the expected right and left hemispheric dominance, respectively. Spatial dissociations are also found within core regions of face and word processing, with a medio-lateral dissociation in the fusiform gyrus (FG) and surrounding sulci, respectively. In the 30% of overlapping face- and word-selective contacts across the VOTC or in the FG and surrounding sulci, between-category-selective amplitudes (faces vs. words) show no-to-weak correlations, despite strong correlations in both the within-category-selective amplitudes (face–face, word–word) and the general visual responses to words and faces. Overall, these observations support the view that category-selective circuitry for faces and written words is largely dissociated in the human adult VOTC.Supplementary Information: The online version contains supplementary material available at 10.1007/s00429-021-02350-4. [less ▲]

The right hemispheric dominance for faces in preschoolers depends on the visual discrimination level.

in Developmental Science (2020), 23(3),

The developmental origin of human adults’ right hemispheric dominance in response to face stimuli remains unclear, in particular because young infants’ right hemispheric advantage in face-selective ... [more ▼]

The developmental origin of human adults’ right hemispheric dominance in response to face stimuli remains unclear, in particular because young infants’ right hemispheric advantage in face-selective response is no longer present in preschool children, before written language acquisition. Here we used fast periodic visual stimulation (FPVS) with scalp electroencephalography (EEG) to test 52 preschool children (5.5 years old) at two different levels of face discrimination: discrimination of faces against objects, measuring face-selectivity, or discrimination between individual faces. While the contrast between faces and nonface objects elicits strictly bilateral occipital responses in children, strengthening previous observations, discrimination of individual faces in the same children reveals a strong right hemispheric lateralization over the occipitotemporal cortex. Picture-plane inversion of the face stimuli significantly decreases the individual discrimination response, although to a much smaller extent than in older children and adults tested with the same paradigm. However, there is only a nonsignificant trend for a decrease in right hemispheric lateralization with inversion. There is no relationship between the right hemispheric lateralization in individual face discrimination and preschool levels of readings abilities. The observed difference in the right hemispheric lateralization obtained in the same population of children with two different paradigms measuring neural responses to faces indicates that the level of visual discrimination is a key factor to consider when making inferences about the development of hemispheric lateralization of face perception in the human brain. [less ▲]

Developmental changes in neural letter-selectivity: A 1-year follow-up of beginning readers.

in Developmental science (2020)

The developmental course of neural tuning to visual letter strings is unclear. Here we tested 39 children longitudinally, at the beginning of grade 1 (6.45 ± 0.33 years old) and 1 year after, with fast ... [more ▼]

The developmental course of neural tuning to visual letter strings is unclear. Here we tested 39 children longitudinally, at the beginning of grade 1 (6.45 ± 0.33 years old) and 1 year after, with fast periodic visual stimulation in electroencephalography to assess the evolution of selective neural responses to letter strings and their relationship with emerging reading abilities. At both grades, frequency-tagged letter strings were discriminated from pseudofont strings (i.e. letter-selectivity) over the left occipito-temporal cortex, with effects observed at the individual level in 62% of children. However, visual words were not discriminated from pseudowords (lexical access) at either grade. Following 1 year of schooling, letter-selective responses showed a specific increase in amplitude, a more complex pattern of harmonics, and were located more anteriorly over the left occipito-temporal cortex. Remarkably, at both grades, neural responses were highly significant at the individual level and correlated with individual reading scores. The amplitude increase in letter-selective responses between grades was not found for discrimination responses of familiar keyboard symbols from pseudosymbols, and was not related to a general increase in visual stimulation responses. These findings demonstrate a rapid onset of left hemispheric letter selectivity, with 1 year of reading instruction resulting in increased emerging reading abilities and a clear quantitative and qualitative evolution within left hemispheric neural circuits for reading. [less ▲]

Impact of teaching methods for reading on neural tuning to words in young poor readers

Poster (2019, September)

The impact of teaching methods on the left hemispheric (LH) specialization for reading in children remains unknown. We tested 42 first graders (mean age: 6.08 years) from schools using both a phonic and a ... [more ▼]

The impact of teaching methods on the left hemispheric (LH) specialization for reading in children remains unknown. We tested 42 first graders (mean age: 6.08 years) from schools using both a phonic and a global method in parallel, behaviorally and with Fast Periodic Visual Stimulation using electroencephalography. 40-sec strings of pseudofonts were displayed at 6Hz, in which were periodically displayed (1.2Hz) either words taught at school with whole-word form rote-learning (global method) or control pseudowords eliciting grapheme-phoneme mappings (phonic method). Control pseudowords elicited LH responses whatever the reading ability. For global words, a difference emerged as a function of group: in good and average readers, responses were stronger in the LH, while in poor readers, global words elicited an atypical bilateral neural pattern due to reduced response amplitude in the LH. These results suggest that difficulties in automatizing GP mappings induce reliance on an alternative visual strategy when available. [less ▲]

Lateralization for faces in prereaders depends on the perceptual processing level: An EEG Fast Periodic Visual Stimulation study

Poster (2019, January)

The developmental origin of human adults’ right hemispheric lateralization to face stimuli is unclear, in particular because young infants’ right hemispheric advantage in face perception is no longer ... [more ▼]

The developmental origin of human adults’ right hemispheric lateralization to face stimuli is unclear, in particular because young infants’ right hemispheric advantage in face perception is no longer present in preschool children, before written language acquisition. Here we used fast periodic visual stimulation (FPVS) with scalp electrophysiology to test 52 preschool children (5 years old) at two levels of face processing (i.e., faces vs. objects, or discrimination between individual faces). While the contrast between faces and nonface objects elicits strictly bilateral occipital responses in children, discrimination of faces on the basis of identity in the same children is associated with a strong right hemispheric lateralization over the occipito-temporal cortex. Inversion of the face stimuli does not modulate right lateralization but significantly decreases the discrimination response. Furthermore, there is no relationship between right hemispheric lateralization in individual face discrimination and preschool levels of letter recognition. These observations suggest that right lateralization for face perception is essentially driven by the necessity to process faces at the level of identity. Overall, they also challenge the view that the adult right hemispheric lateralization for face perception emerges late and slowly during childhood due to increased competition with left lateralized posterior network for reading. [less ▲]

The non-linear development of the right hemispheric specialization for human face perception

in Neuropsychologia (2019), 126

The developmental origins of human adults’ right hemispheric specialization for face perception remain unclear. On the one hand, infant studies have shown a right hemispheric advantage for face perception ... [more ▼]

The developmental origins of human adults’ right hemispheric specialization for face perception remain unclear. On the one hand, infant studies have shown a right hemispheric advantage for face perception. On the other hand, it has been proposed that the adult right hemispheric lateralization for face perception slowly emerges during childhood due to reading acquisition, which increases left lateralized posterior responses to competing written material (e.g., visual letters and words). Since methodological approaches used in infant and children typically differ when their face capabilities are explored, resolving this issue has been difficult. Here we tested 5- year-old preschoolers varying in their level of visual letter knowledge with the same fast periodic visual stimulation (FPVS) paradigm leading to strongly right lateralized electrophysiological occipito-temporal face-selective responses in 4- to 6-month-old infants (de Heering and Rossion, 2015). Children's face-selective response was quantitatively larger and differed in scalp topography from infants’, but did not differ across hemispheres. There was a small positive correlation between preschoolers’ letter knowledge and a non-normalized index of right hemispheric specialization for faces. These observations show that previous discrepant results in the literature reflect a genuine nonlinear development of the neural processes underlying face perception and are not merely due to methodological differences across age groups. We discuss several factors that could contribute to the adult right hemispheric lateralization for faces, such as myelination of the corpus callosum and reading acquisition. Our findings point to the value of FPVS coupled with electroencephalography to assess specialized face perception processes throughout development with the same methodology [less ▲]

Automatic discrimination of digits and letters in first graders and adults: an EEG Fast Periodic Visual Stimulation study.

Poster (2018, June)

Both letters and digits are arbitrary visual shapes that are distinguished into categories only after cultural acquisition. The observation that digits are easier to identify than letters has been ... [more ▼]

Both letters and digits are arbitrary visual shapes that are distinguished into categories only after cultural acquisition. The observation that digits are easier to identify than letters has been repeatedly reported in the literature (Shubert, 2017). In the present study, we used a Fast Periodic Visual Stimulation approach with EEG recordings to assess the automatic discrimination of letters and digits from each other in 1st grade children (N=17) and in adults (N=18). Participants viewed 40 sec sequences (3 repetitions per condition) of frequent stimuli (letters or digits) at a fast periodic rate (adults: 10Hz, children: 6Hz), in which rare stimuli (the other category of alphanumeric symbols) were periodically inserted (every five items, e.g., adults: at 2Hz, children: at 1.2Hz). Results showed discrimination responses in both groups in posterior occipito-temporal regions with clear changes in lateralization patterns. In children, stimuli contained only single elements. Responses were right-lateralized for digits among letters, and revealed a trend for left-lateralization for letters among digits. In adults, when stimuli contained only 1 character, both letters and digits gave rise to responses in the RH. However, when strings of characters were presented, then letters were discriminated from digits in the LH. These findings show a developmental pattern where single elements in children seem to be processed like strings of elements in adults. [less ▲]

Neurosciences et lecture

Presentation (2018)

Selective visual representation of letters and words in the left ventral occipito-temporal cortex with intracerebral recordings.

in Proceedings of the National Academy of Sciences of the United States of America (2018), 115(32), 7595-7604

We report a comprehensive cartography of selective responses to visual letters and words in the human ventral occipito-temporal cortex (VOTC) with direct neural recordings, clarifying key aspects of the ... [more ▼]

We report a comprehensive cartography of selective responses to visual letters and words in the human ventral occipito-temporal cortex (VOTC) with direct neural recordings, clarifying key aspects of the neural basis of reading. Intracerebral recordings were performed in a large group of patients (n = 37) presented with visual words inserted periodically in rapid sequences of pseudofonts, nonwords, or pseudowords, enabling classification of responses at three levels of word processing: letter, prelexical, and lexical. While letter-selective responses are found in much of the VOTC, with a higher proportion in left posterior regions, prelexical/lexical responses are confined to the middle and anterior sections of the left fusiform gyrus. This region overlaps with and extends more anteriorly than the visual word form area typically identified with functional magnetic resonance imaging. In this region, prelexical responses provide evidence for populations of neurons sensitive to the statistical regularity of letter combinations independently of lexical responses to familiar words. Despite extensive sampling in anterior ventral temporal regions, there is no hierarchical organization between prelexical and lexical responses in the left fusiform gyrus. Overall, distinct word processing levels depend on neural populations that are spatially intermingled rather than organized according to a strict postero-anterior hierarchy in the left VOTC. [less ▲]