Visual crowding is the difficulty in identifying an object when surrounded by neighbouring flankers, representing a bottleneck for object perception. Crowding arises not only from the activity of visual areas but also from parietal areas and fronto-parietal network activity. Parietal areas would provide the dorsal-to-ventral guidance for object identification and the fronto-parietal network would modulate the attentional resolution. Several studies highlighted the relevance of beta oscillations (15-25 Hz) in these areas for visual crowding and other connatural visual phenomena. In the present study, we investigated the differential contribution of beta oscillations in the parietal cortex and fronto-parietal network in the resolution of visual crowding. During a crowding task with letter stimuli, high-definition transcranial Alternating Current Stimulation (tACS) in the beta band (18 Hz) was delivered bilaterally on parietal sites, on the right fronto-parietal network, and in a sham regime. Resting-state EEG was recorded before and after stimulation to measure tACS-induced aftereffects. The influence of crowding was reduced only when tACS was delivered bilaterally on parietal sites. In this condition, beta power was reduced after the stimulation. Furthermore, the magnitude of tACS-induced aftereffects varied as a function of individual differences in beta oscillations. Results corroborate the link between parietal beta oscillations and visual crowding, providing fundamental insights on brain rhythms underlying the dorsal-to-ventral guidance in visual perception and suggesting that beta tACS can induce plastic changes in these areas. Remarkably, these findings open new possibilities for neuromodulatory interventions for disorders characterised by abnormal crowding, such as dyslexia.

Lip-reading, i.e., the ability to recognize speech using only visual cues, plays a fundamental role in audio-visual speech processing, intelligibility, and comprehension. This capacity is integral to language development and functioning; it emerges in early development, and it slowly evolves. By linking psycholinguistics, psychophysics, and neurophysiology, the present narrative review explores the development and significance of lip-reading across different stages of life, highlighting its role in human communication in both typical and atypical development, e.g., in the presence of hearing or language impairments. We examined how relying on lip-reading becomes crucial when communication occurs in noisy environments and, on the contrary, the impacts that visual barriers can have on speech perception. Finally, this review highlights individual differences and the role of cultural and social contexts for a better understanding of the visual counterpart of speech.

The temporal relationship between incoming signals is crucial in determining whether multisensory information is integrated into unitary percepts. Temporal binding windows (TBWs) define the time range within which multisensory inputs are highly likely to be perceptually integrated, even if asynchronous. TBWs widen with stimulus complexity and neurodevelopmental conditions (e.g., autism and schizophrenia), yet the key factors underlying their malleability remain unclear. The (quasi)rhythmic properties of sensory inputs, frequently embedded in natural stimuli (e.g., speech), are among the possible exogenous modulators. Indeed, stimulus spectral features can influence the alignment of neural excitability across sensory regions, synchronizing brain rhythms with external rhythmic patterns through phase‐reset mechanisms and neural entrainment. In a series of psychophysical studies, we presented simultaneity judgement tasks with pulsing audio‐visual (AV) streams amplitude‐modulated according to different regular frequencies or following purely rhythmic vs. quasi‐rhythmic (speech‐like) envelopes. Results show that TBWs decrease as the stimulus frequency increases and that speech‐like streams are integrated across larger TBWs. These findings highlight the importance of stimulus spectral structure in shaping multisensory perception. Furthermore, they show that quasi‐rhythmic spectrotemporal features of speech‐like streams induce more tolerant cross‐modal temporal processing even when the leading stimulation frequency is controlled for, putatively reflecting an adaptation to the variable rhythmic structure of natural speech. Our results align with neurophysiological accounts of neural entrainment and motivate future research in clinical populations with multisensory processing deficits.