Biology subjects

Lochy, A.

Publications and source records attributed to Lochy, A..

8 recordsLinked to original sources

bioRxiv2026

Semantic distance differently modulates FPVS-EEG responses to words and pictures

The organization of semantic knowledge within the brain has long been studied through various theoretical frameworks and is still a matter of debate. Many studies that have helped advancing our knowledge about this topic have approached it in the context of its deterioration, notably in patients with semantic dementia. In healthy subjects, the question whether and how semantic distance between concepts represented by picture or word stimuli influences brain responses remains understudied. In this study with 24 healthy subjects, we used electroencephalography (EEG) recordings coupled with a fast periodic visual stimulation (FPVS) approach, for the first time, to assess the semantic distance effect with different stimulus modalities. Picture or word stimuli from a reference category (birds) appeared every fourth item among a 4-Hz stream of either man-made objects (forming the high distance [HD] condition) or other animals (low distance [LD] condition). Within a few minutes of recording, EEG responses were observed at the pre-determined frequency of the reference category presentation (at 1 Hz), suggesting its exemplars were activated at least sufficiently to be automatically discriminated from different superordinate (HD) and basic (LD) categories, for both pictures and words. Pictures and words elicited a different pattern of response to semantic distance, with larger amplitudes for HD than LD conditions for pictures but a reversed pattern of somewhat greater amplitudes for LD than HD conditions for words. Our findings support a similarity-based structure of semantic representations and provide evidence for a differential mapping between semantic and picture/word surface representations.

neuroscience↗

bioRxiv2025

Lexical brain responses in 10-year-old children are impaired in dyslexia: an FPVS-EEG study

The developmental origin of the left occipitotemporal cortex specialization for automatic lexical access from vision remains unclear. Here we investigated cortical specialization for print processing in children with or without dyslexia, focusing on two distinct tuning levels: coarse-grained tuning for letter/symbol discrimination, and fine-grained tuning for word/pseudoword discrimination. 10-year-old typical readers (n=24) and children with dyslexia (n=14) were tested with electroencephalography (EEG) and fast periodic visual stimulation (FPVS), viewing streams of stimuli at a relatively fast rate (6Hz) for 40 seconds with deviant categories every 5 items (at 6Hz/5=1.2Hz). Deviant words or pseudowords among pseudo-font strings elicited clear coarse ocicpito-temporal discrimination responses significantly larger over the left than the right hemisphere (LH), numerically larger in typical readers. Unlike in adults, these responses were unaffected by lexicality. Deviant regular or irregular words among matched pseudowords generated a finer-grained word-selective response only over the LH. While irregular words elicited similar brain responses in both groups, regular words were not discriminated from pseudowords in children with dyslexia. These results demonstrate the sensitivity of FPVS-EEG to implicitly detect lexical neural responses in 10 years old children within a few minutes, as well as atypical lexical processing in children with dyslexia.

neuroscience↗

bioRxiv2024

Word-selective EEG/MEG responses in the English language obtained with Fast Periodic Visual Stimulation (FPVS)

Fast periodic visual stimulation (FPVS) allows the recording of objective brain responses of human word discrimination (i.e., reproducible word-category-selective responses) with a high signal-to-noise ratio. This approach has been successfully employed over the last decade in a number of scalp electroencephalography (EEG) studies. Three important advances were achieved in this study: (1) robust measures of written word-selective responses with this approach have not been reported in English; (2) responses have only been reported in EEG but not with MEG, and (3) without source localization. Thus, we presented English words periodically (2 Hz) among different types of letter strings (10Hz; consonant strings, non-words, pseudowords) whilst recording simultaneous EEG and MEG in 25 participants who performed a simple non-linguistic color detection task. Data were analyzed in sensor and in source space (L2-minimum-norm estimation, MNE). With only 4 minutes of stimulation we observed a robust word discrimination response in each condition including, importantly, even when words were embedded in word-like pseudowords. This response was larger in nonwords and largest in consonant strings. We observed left-lateralized responses in all conditions in the majority of our participants. Cluster-based permutation tests revealed that these responses were left-lateralized in sensor as well as in source space, with peaks in left posterior regions. Our results demonstrate that the FPVS paradigm can elicit robust English word-discrimination responses in EEG and MEG within only a few minutes of recording time. Together with source estimation, this can provide novel insights into the neural basis of visual word recognition in healthy and clinical populations.

neuroscience↗

bioRxiv2023

Linguistic and attentional factors -not statistical regularities- contribute to word-selective neural responses with FPVS-oddball paradigms

In recent years, a fast periodic oddball-like paradigm has proved to be highly sensitive to measure category-selective visual word representation and characterize its development and neural basis. In this approach, deviant words are inserted in rapid streams of base stimuli every nth occurrence (e.g., Lochy et al., 2015). To understand the nature of word-selective representation and improve its measurement, we tested 22 adults with EEG, assessing the impact of discrimination coarseness (deviant words among nonwords or pseudowords), the relative frequency of item repetition (set size or item repetition controlled for deviant vs. base stimuli), and the nature of the orthogonal attentional task (focused or deployed spatial attention). In all stimulation sequences, base stimuli were presented at 10 Hz, with words inserted every 5 stimuli generating word-selective responses in the EEG spectra at 2 Hz and harmonics. Word-selective occipito-temporal responses were robust at the individual level, left-lateralized and sensitive to wordlikeness of base stimuli, being stronger in the coarser categorical contrast (among nonwords). Amplitudes were not affected by item repetition, showing that implicit statistical learning about a relative token frequency difference for deviant stimuli does not contribute to the word-selective neural activity, at least with relatively large stimulus set sizes (n=30). Finally, the broad attentional deployment task produced stronger responses than a focused task, an important finding for future studies in the field. Taken together, these results confirm the linguistic nature of word-selective responses, strengthen the validity and increase the sensitivity of the FPVS-EEG oddball paradigm to measure visual word recognition. HighlightsO_LIWord-selective responses measured in fast periodic visual stimulation with EEG are linguistic in nature C_LIO_LIWord-selective responses reflect prelexical or lexical processes depending on the contrast (words in nonwords or pseudowords respectively) C_LIO_LIUsing sufficiently large sets (30 items) prevents the extraction of statistical regularities and hence, statistical learning C_LIO_LIUsing an orthogonal task involving broad, rather than focused, spatial attention increases amplitude of the neural responses C_LIO_LISensitivity of the paradigm to detect significant responses at the individual level is very good (95% for prelexical and about 80% for lexical word responses) C_LI

neuroscience↗

bioRxiv2021

A neural signature of automatic lexical access in bilinguals

Bilingualism is often associated with beneficial effects on cognitive control and top-down processes. The present study aimed at bypassing these processes to assess automatic visual word recognition in bilinguals. Using fast periodic visual stimulation, we recorded frequency-tagged word-selective EEG responses in French monolinguals and late bilinguals (German native, French as second language). Words were presented centrally within rapid (10 Hz) sequences of letter strings varying in word-likeness, i.e., consonant strings, non-words, pseudo-words, while participants performed an orthogonal task. Automatic word-selective brain responses in the occipito-temporal cortex arose almost exclusively for the languages mastered by participants: two in bilinguals vs. one in monolinguals. Importantly, the amplitude of bilinguals responses to words within consonant strings were unaffected by the native vs. late-learnt status of the language. Furthermore, for all and only known languages, word-selective responses were reduced by embedding them in pseudo-words relative to non-words, both derived from the same language as the words. This word-likeness effect highlights the lexical nature of the recorded brain visual responses. A cross-language word-likeness effect was observed only in bilinguals and only with pseudo-words derived from the native language, indicating an experience-based tuning to language. Taken together these findings indicate that the amount of exposure to a language determines the engagement of neural resources devoted to word processing in the occipito-temporal visual cortex. We conclude that automatic lexical coding occurs at early visual processing in bilinguals and monolinguals alike, and that language exposure determines the competition strength of a language. Significance StatementBilingualism and its possible impact on automatic processes have rarely attracted interest, contrary to bilingualism and its mutual relation with the executive functions. We assessed automatic visual word recognition in bi- and monolingual individuals while purposively bypassing executive functions. Visual brain potentials frequency tagged to words, that were flashed in rapid trains of strings with varying word-likeness degrees, exposed the automatic encoding of word-form as well as language identity at early stages of visual word processing within the occipito-temporal visual cortex. The mechanisms involved in both encoding processes reflect experience-based activity as the one characterizing tight-tuned neurons in the VWFA. Our findings provide a novel framework to understand the mechanisms behind the incredible efficiency of bilinguals in handling multiple languages.

neuroscience↗

bioRxiv2020

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

The extent to which faces and written words share neural circuitry in the human brain is actively debated. Here we compared face-selective and word-selective responses in a large group of patients (N = 37) implanted with intracerebral depth electrodes in the ventral occipito-temporal cortex (VOTC). Both face-selective (i.e., significantly different responses to faces vs. nonface visual objects) and word-selective (i.e., significantly different responses to words vs. pseudofonts) neural activity is isolated through 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 contacts show either only face-selectivity or only word-selectivity, 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, while a postero-anterior dissociation is found in the inferior occipital gyrus (IOG). Only 30% of the significant contacts show both face- and word-selective responses. Critically, in these contacts, across the VOTC or in the FG and surrounding sulci, between-category selective-amplitudes (faces vs. words) showed 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, we conclude that category-selectivity for faces and written words is largely dissociated in the human VOTC. Significance StatementIn modern human societies, faces and written words have become arguably the most significant stimuli of the visual environment. Despite extensive research in neuropsychology, electroencephalography and neuroimaging over the past three decades, whether these two types of visual signals are recognized by similar or dissociated processes and neural networks remains unclear. Here we provide an original contribution to this outstanding scientific issue by directly comparing frequency-tagged face- and word-selective neural responses in a large group of epileptic patients implanted with intracerebral electrodes covering the ventral occipito-temporal cortex. While general visual responses to words and faces show significant overlap, the respective category-selective responses are neatly dissociated in spatial location and magnitude, pointing to largely dissociated processes and neural networks.

neuroscience↗

bioRxiv2018

Teaching methods shape neural tuning to visual words in beginning readers

The impact of global vs. phonics teaching methods for reading on the emergence of left hemisphere neural specialization for word recognition is unknown in children. We tested 42 first graders behaviorally and with electroencephalography with Fast Periodic Visual Stimulation to measure selective neural responses to letter strings. Letter strings were inserted periodically (1/5) in pseudofonts in 40sec sequences displayed at 6Hz and were either words globally taught at school, eliciting visual whole-word form recognition (global method), or control words/pseudowords eliciting grapheme-phoneme mappings (phonic method). Selective responses (F/5, 1.2Hz) were left lateralized for control stimuli but bilateral for globally taught words, especially in poor readers. These results show that global method instruction induces activation in the right hemisphere, involved in holistic processing and visual object recognition, rather than in the specialized left hemisphere for reading. Poor readers, given their difficulties in automatizing grapheme-phoneme mappings, mostly rely on this alternative inadequate strategy.

neuroscience↗

bioRxiv2017

The Non-Linear Development Of The Right Hemispheric Specialization For Human Face Perception

The developmental origins of human adults right hemispheric specialization for face perception remain unclear. On the one hand, infant studies have generally shown a right hemispheric advantage for face perception. On the other hand, the adult right hemispheric lateralization for face perception is thought to slowly emerge during childhood, due to reading acquisition, which increases left lateralized posterior responses to competing written material (i.e., visual letters and words). Since methodological approaches used in infant and children usually differ, 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 & Rossion, 2015). Childrens face-selective response was much larger and more complex than in infants, but did not differ across hemispheres. However, there was a small positive correlation between preschoolers letter knowledge and their right hemispheric specialization for faces. These observations suggest that several factors contribute to the adult right hemispheric lateralization for faces, and point to the value of FPVS coupled with electroencephalography to assess specialized face perception processes throughout development with the same methodology.

neuroscience↗