Is human face recognition lateralized to the right hemisphere due to neural competition with left‑lateralized visual word recognition? A critical review

The right hemispheric lateralization of face recognition, which is well documented and appears to be specific to the human species, remains a scientific mystery. According to a long-standing view, the evolution of language, which is typically substantiated in the left hemisphere, competes with the cortical space in that hemisphere available for visuospatial processes, including face recognition. Over the last decade, a specific hypothesis derived from this view according to which neural competition in the left ventral occipito-temporal cortex with selective representations of letter strings causes right hemispheric lateralization of face recognition, has generated considerable interest and research in the scientific community. Here, a systematic review of studies performed in various populations (infants, children, literate and illiterate adults, left-handed adults) and methodologies (behavior, lesion studies, (intra)electroencephalography, neuroimaging) offers little if any support for this reading lateralized neural competition hypothesis. Specifically, right-lateralized face-selective neural activity already emerges at a few months of age, well before reading acquisition. Moreover, consistent evidence of face recognition performance and its right hemispheric lateralization being modulated by literacy level during development or at adulthood is lacking. Given the absence of solid alternative hypotheses and the key role of neural competition in the sensory–motor cortices for selectivity of representations, learning, and plasticity, a revised language-related neural competition hypothesis for the right hemispheric lateralization of face recognition should be further explored in future research, albeit with substantial conceptual clarification and advances in methodological rigor

Novel visual word tracked with FPVS-EEG

Reading is one of the most important human skills and has been studied for years with different techniques. EEG frequency tagging with electroencephalography (EEG) recordings proved efficient to measure the neural basis of visual word recognition. Here we investigate the emergence of novel neural representations for written words in 32 adults (21 females; age mean=21.78; range=17-32 years old) who were tested with EEG before and after learning 32 rare French words according to two different methods. Half of the words were provided with orthographic and phonological information only, while the other half were also provided with explicit semantic information. Participants were tested twice at one-week interval. During the first session, cognitive and language abilities were assessed, and a lexical decision task was performed. In the second session, they were capped with a 64 Biosemi system (EEG) for two EEG recordings (pre and post-learning), and a post-test lexical decision task was performed. Novel words were taught by blocs of 8, through different short learning tasks (matching, typing, etc…), and were counterbalanced so that they were either learned with orthography + phonology only (OP hereafter) or orthography + phonology + semantic (OPS hereafter). We used fast periodic visual stimulation (FPVS) coupled with EEG to measure selective neural responses to words. Base stimuli (pseudowords) were displayed at 10Hz during 1 min, and periodic deviant stimuli (words) occured every fifth stimulus (at 10Hz/5 thus 2Hz). Responses to deviant stimuli at 2Hz indicate that words have been automatically discriminated from pseudowords. Here we contrasted 4 sequence types displaying words (learned words OP, learned words OPS, unknown words, and known words) among respectively matched pseudowords. Every condition was repeated 4 times for a total of 16 sequences of 60 seconds. EEG results show a significant learning effect (p<0.001), with larger word-selective responses over the left occipital-temporal cortex at post-test with both methods, while no pre/post difference was seen for control conditions (known and unknown words). Contrary to our hypothesis, larger amplitudes were found with the OP method than with the OPS method (p=0.036). These results reveal that discrimination of learned word among pseudowords was stronger when learnt with the orthographic method. Moreover, behavioral lexical decision data reveal that the new lexical trace of the learned words induced significant increases in reaction times both for novel words’ lexical neighbors and for 1-letter close pseudowords, suggesting competition effects arising with new lexicalizations. Those effects were stronger for OP words, as in EEG responses. This might indicate that the semantic method, implemented here by simultaneous image and word presentation during learning, drags the participant’s attention away from the orthographic form. This suggestion is supported by the fact that successful OPSs learning took longer than OP learning . Our findings open new perspectives to track novel word learning using EEGU-AGR-7143 - C21/SC/16241557/READINGBRAIN (01/09/2022 - 31/08/2025) - LOCHY Aliett

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 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 methodolog

Impact of learning to read in a mixed approach on neural tuning to words in beginning readers

The impact of learning to read in a mixed approach using both the global and phonics teaching methods on the emergence of left hemisphere neural specialization for word recognition is yet unknown in children. Taking advantage of a natural school context with such a mixed approach, we tested 42 first graders behaviorally and with Fast Periodic Visual Stimulation using electroencephalographic recordings (FPVS-EEG) to measure selective neural responses to letter strings. Letter strings were inserted periodically (1/5) in pseudofonts in 40 s sequences displayed at 6 Hz and were either words globally taught at school, that could therefore be processed by visual whole-word form recognition (global method), or control words/pseudowords eliciting graphemephoneme (GP) mappings (phonics method). Results show that selective responses (F/5, 1.2 Hz) were left lateralized for control stimuli that triggered GP mappings but bilateral for globally taught words. It implies that neural mechanisms recruited during visual word processing are influenced by the nature of the mapping between written and spoken word forms. GP mappings induce left hemisphere discrimination responses, and visual recognition of whole-word forms induce bilateral responses, probably because the right hemisphere is relatively more involved in holistic visual object recognition. Splitting the group as a function of the mastery of GP mappings into “good” and “poor” readers strongly suggests that good readers actually processed all stimuli (including global words) predominantly with their left hemisphere, while poor readers showed bilateral responses for global words. These results show that in a mixed approach of teaching to read, global method instruction may induce neural processes that differ from those specialized for reading in the left hemisphere. Furthermore, given their difficulties in automatizing GP mappings, poor readers are especially prone to rely on this alternative visual strategy. A preprint of this paper has been released on Biorxiv (van de Walle de Ghelcke et al., 2018)

Is there an optimal stimulation rate for frequency-tagged visual word-selective responses?

peer reviewedThe existence of inter-individual variability in hemispheric dominance for word recognition processes still needs to be understood. Unfortunately, there are methodological and practical limitations in using neuroimaging techniques and linguistic tasks to determine language lateralisation. Fast Periodic Visual Stimulation (FPVS) coupled with EEG provides objective and sensitive measures of visual recognition processes without explicit tasks required. Indeed, by using a visual word oddball paradigm in which every 5th of the 10 images presented in one second (10Hz base stimulation), a word is inserted (2Hz) in rapid streams of non-words or pseudo-words, a robust index of lexical representation in the left occipito-temporal cortex has been revealed (Lochy et al., 2015). Here we use this promising technique, to determine if there is an optimal stimulation rate for frequency-tagged visual word-selective responses. For this, words are embedded in streams of non-words (i.e., pre-lexical discrimination) or pseudo-words (i.e., lexical discrimination) at a periodic rate, giving rise to frequency-tagged word-selective responses. We used four different frequencies (4 to 20Hz base frequency), to assess if word responses vary in amplitude and topography according to stimulation rate. For all frequencies, words are inserted at 1Hz, at the last frame of the base frequency except for one frequency at 10Hz (i.e., base stimulation) with 2Hz for the oddball frequency. 41 participants were tested both in EEG-FPVS and with reading tests. Reading performance was measured to see if visual word-selective response is modulated by reading speed and/or performance. We found differences in amplitude according to the level of discrimination of the word with a significantly higher amplitude at the visual word-selective response for pre-lexical than lexical discrimination. For both conditions, amplitude and topography differ according to stimulation rate with a strong left activation found at 4Hz and at 10Hz stimulation rate (2Hz at the oddball frequency). Even if responses are more bilateral at 4Hz in non-words condition, no significant difference was found between the left amplitude of these two frequencies. We then found a significant correlation only at 4Hz for lexical word discrimination with reading speed. The faster a person reads a word, the higher the amplitude of the word-selective response in a lexical discrimination over the occipitotemporal cortex. These results suggest that optimal frequencies of stimulation as well as lateralisation vary with the type of word-selective response. However, 4Hz seems to be the most adapted frequency to lead to a stronger left response for word-selective discrimination depending on the reading performance

Intracerebral electrical stimulation of the left word-selective temporal cortex induces pure alexia

peer reviewedThe ability to read relies on the rapid mapping of perceived visual letters and their combinations (i.e., visual word forms) to phonology and meaning. The central role of the left ventral occipito-temporal cortex (VOTC) in processing letter strings, initially suggested by pure alexia in lesion studies, is now widely accepted. While this region has been intensely studied with functional MRI, direct electrical stimulation (DES) has rarely been used, although it allows a more direct assessment of causality between region(s) and function(s). Moreover, the few DES case studies reported did not provide stringent evaluation of the stimulation effect on reading performance. Here we report a comprehensive case of pure alexia during DES of the left VOTC (subject LV, female, 38 y.o, implanted with SEEG electrodes for refractory epilepsy). During DES of the left posterior occipito-temporal sulcus, but not of other sites, LV was transiently impaired at reading single words (performance on paper without time constraint: 99% correct before and after stimulation vs. 71% during stimulation) but was still able to slowly read letter-by-letter. LV was also impaired at making lexical decision on written words/pseudo-words (performance on paper: 100% vs. 75%; on computer screen: 92% vs. 72%), showing that she had impaired access to the lexico-semantic representation of the words. By contrast, performance was intact during stimulation for oral naming, auditory naming, reading numbers, writing, auditory lexical decision or semantic matching of pictures. Independent functional mapping using a frequency-tagging approach in SEEG showed that the stimulated site was located in a highly word-selective region. Altogether, our results show that DES of the word-selective left VOTC induced pure alexia remarkably selective to words readin

L'écriture des nombres arabes : études à la table digitalisante

Doctorat en sciences psychologiques (PSY 3)--UCL, 200