Biology subjects

Retsa, C.

Publications and source records attributed to Retsa, C..

7 recordsLinked to original sources

bioRxiv2025

The brain dynamics of congenitally blind people seeing faces with sound

Sensory substitution devices (SSDs) convert images to sounds to equip blind individuals with nominally visual functions, like face or letter sensitivity. Prior studies showed that image-to-sound SSDs engage cortices ordinarily specialised for visual functions. However, the brain dynamics of SSD-supported perception remains unknown. Either visual cortices are the first locus of discrimination of SSD percepts, or their activation is a byproduct of perceptual processes unfurling elsewhere, such as in auditory cortices. Resolving this uncertainty is critical for understanding the contribution of visual cortices to mechanisms subserving SSD-induced perceptions in the blind. Using electrical neuroimaging of EEG data from congenitally blind adults, we show for the first time that visual cortices are the earliest site of face and letter sensitivity when conveyed via SSDs, though with distinct temporal dynamics and spatial localizations. In the case of faces versus scrambled faces, differences first manifested at 460ms post-stimulus onset as topographic EEG modulations that were in turn localized to a network of right-hemisphere regions, including the fusiform face area (FFA) as well as lateral occipital cortices. In the case of discerning vertically versus horizontally oriented letter shapes, differences first manifested at 370ms post-stimulus onset as topographic EEG modulations that were localized to a network of left-hemisphere regions, including the occipital pole and the occipito-temporal junction extending into the angular gyrus. Notably, early-latency auditory evoked potentials did not differ based on visual properties of the soundscapes. These collective data support the proposition that responses to soundscapes are routed to brain circuits ordinarily specialized for processing visual information and that these circuits are the loci of the initial discriminant processes. By providing the temporal dynamics of SSD perception, our findings provide unique evidence for the theory that cortices are characterised by task-contingent functional organisation. HighlightsO_LISensory substitution devices (SSDs) provide the blind access to visual information C_LIO_LIBrain dynamics in visual cortices to SSD-conveyed object images are unknown C_LIO_LIEarly EEG sensitivity for faces and letters was localized to the visual cortex C_LIO_LIThe blind visual cortex takes part in early SSD processing for visual categories C_LI eTOC blurbWe characterise for the first time the brain dynamics of the blind using soundscapes for face and letter discrimination. Faces recruited the FFA at 460ms post-stimulus onset, whereas letters recruited the occipital pole, occipito-temporal junction, and angular gyrus at 370ms post-stimulus onset. Our findings of the temporal dynamics of SSD perception uniquely support the theory that cortices are characterised by task-selective sensory-independent functional organisation.

neuroscience↗

bioRxiv2023

Longstanding auditory sensory and semantic differences in preterm born children

More than 10% of births are preterm, and the long-term consequences on sensory and semantic processing of non-linguistic information remain poorly understood. 17 very preterm-born children (born at <33 weeks gestational age) and 15 full-term controls were tested at 10 years old with an auditory object recognition task, while 64-channel auditory evoked potentials (AEPs) were recorded. Sounds consisted of living (animal and human vocalizations) and manmade objects (e.g. household objects, instruments, and tools). Despite similar recognition behavior, AEPs strikingly differed between full-term and preterm children. Starting at 50ms post-stimulus onset, AEPs from preterm children differed topographically from their full-term counterparts. Over the 108-224ms post-stimulus period, full-term children showed stronger AEPs in response to living objects, whereas preterm born children showed the reverse pattern; i.e. stronger AEPs in response to manmade objects. Differential brain activity between semantic categories could reliably classify children according to their preterm status. Moreover, this opposing pattern of differential responses to semantic categories of sounds was also observed in source estimations within a network of occipital, temporal and frontal regions. This study highlights how early life experience in terms of preterm birth shapes sensory and object processing later on in life. HighlightsO_LIHow very preterm birth affects nonlinguistic auditory processes in school-age is unknown C_LIO_LIWe measured auditory evoked potentials to environmental sounds C_LIO_LISensory processing differences manifested from 50ms post-stimulus onwards C_LIO_LISemantic processing differences manifested at 108-224ms post-stimulus C_LIO_LIClassification of preterm status was possible from semantic processing differences C_LI

neuroscience↗

bioRxiv2020

Uncovering the mechanisms of real-world attentional control over the course of primary education

Schooling may shape childrens abilities to control their attention, but it is unclear if this impact extends from control over visual objects to encompass multisensory objects, which are more typical of everyday environments. We compared children across three primary school grades ([country] 1st, 3rd, and 5th grade) on their performance on a game-like audio-visual attentional control task, while recording their EEG. Behavioral markers of visual attentional control were present from 3rd grade (after 2 years of schooling), whereas multisensory attentional control was not detected in any group. However, multivariate whole-brain EEG analyses ( electrical neuroimaging) revealed stable patterns of brain activity that indexed both types of attentional control - visual control in all groups, and multisensory attentional control from 3rd grade onwards. Multivariate EEG approaches can uncover otherwise undetectable mechanisms of attentional control over visual and multisensory objects and characterize how they differ at different educational stages. Lay AbstractWe measured how visual and audiovisual distractors differ in capturing the attention of 1st- to 5th-graders while recording the childrens brain activity. Brain activity results showed that all children were sensitive to visual distraction, and from 3rd grade onwards, children were also sensitive to audiovisual distraction. These results deepen our understanding of how school children control their attention in everyday environments, which are made up of information that stimulates multiple senses at a time.

neuroscience↗

bioRxiv2020

How we pay attention in naturalistic settings

Research on attentional control has largely focused on single senses and the importance of behavioural goals in controlling attention. However, everyday situations are multisensory and contain regularities, both likely influencing attention. We investigated how visual attentional capture is simultaneously impacted by top-down goals, the multisensory nature of stimuli, and the contextual factors of stimulis semantic relationship and temporal predictability. Participants performed a multisensory version of the Folk et al. (1992) spatial cueing paradigm, searching for a target of a predefined colour (e.g. a red bar) within an array preceded by a distractor. We manipulated: 1) stimulis goal-relevance via distractors colour (matching vs. mismatching the target), 2) stimulis multisensory nature (colour distractors appearing alone vs. with tones), 3) the relationship between the distractor sound and colour (arbitrary vs. semantically congruent) and 4) the temporal predictability of distractor onset. Reaction-time spatial cueing served as a behavioural measure of attentional selection. We also recorded 129-channel event-related potentials (ERPs), analysing the distractor-elicited N2pc component both canonically and using a multivariate electrical neuroimaging framework. Behaviourally, arbitrary target-matching distractors captured attention more strongly than semantically congruent ones, with no evidence for context modulating multisensory enhancements of capture. Notably, electrical neuroimaging of surface-level EEG analyses revealed context-based influences on attention to both visual and multisensory distractors, in how strongly they activated the brain and type of activated brain networks. For both processes, the context-driven brain response modulations occurred long before the N2pc time-window, with topographic (network-based) modulations at ~30ms, followed by strength-based modulations at ~100ms post-distractor onset. Our results reveal that both stimulus meaning and predictability modulate attentional selection, and they interact while doing so. Meaning, in addition to temporal predictability, is thus a second source of contextual information facilitating goal-directed behaviour. More broadly, in everyday situations, attention is controlled by an interplay between ones goals, stimulis perceptual salience, meaning and predictability. Our study calls for a revision of attentional control theories to account for the role of contextual and multisensory control.

neuroscience↗

bioRxiv2020

A psychophysically tuned computational model of human primary visual cortex produces geometric optical illusions

Geometrical optical illusion (GOIs) are mismatches between physical stimuli and perception. GOIs provide an access point to study the interplay between sensation and perception, yet there is scant quantitative investigation of the extent to which different GOIs rely on similar or distinct brain mechanisms. We addressed this knowledge gap. First, 30 healthy adults reported quantitatively their perceptual biases with three GOIs, whose physical properties parametrically varied on a trial-by-trial basis. Biases observed with one GOI were unrelated to those observed with another GOI, suggestive of (partially) distinct underlying mechanisms. Next, we used these psychophysical results to tune a computational model of primary visual cortex that combines parameters of orientation, selectivity, intra-cortical connectivity, and long-range interactions. We showed that similar biases could be generated in-silico, mirroring those observed in humans. Such results provide a roadmap whereby computational modelling, informed by human psychophysics, can reveal likely mechanistic underpinnings of perception.

neuroscience↗

bioRxiv2020

The development of attentional control mechanisms in multisensory environments

Outside the laboratory, people need to pay attention to relevant objects that are typically multisensory, but it remains poorly understood how the underlying neurocognitive mechanisms develop. We investigated when adult-like mechanisms controlling ones attentional selection of visual and multisensory objects emerge across childhood. Five-, 7-, and 9-year-olds were compared with adults in their performance on a computer game-like multisensory spatial cueing task, while 129-channel EEG was simultaneously recorded. Markers of attentional control were behavioural spatial cueing effects and the N2pc ERP component (analysed traditionally and using a multivariate electrical neuroimaging framework). In behaviour, adult-like visual attentional control was present from age 7 onwards, whereas multisensory control was absent in all children groups. In EEG, multivariate analyses of the activity over the N2pc time-window revealed stable brain activity patterns in children. Adult-like visual-attentional control EEG patterns were present age 7 onwards, while multisensory control activity patterns were found in 9-year-olds (albeit behavioural measures showed no effects). By combining rigorous yet naturalistic paradigms with multivariate signal analyses, we demonstrated that visual attentional control seems to reach an adult-like state at ~7 years, before adult-like multisensory control, emerging at ~9 years. These results enrich our understanding of how attention in naturalistic settings develops. HighlightsO_LIBy age 7, children showed adult-like task-set contingent attentional capture in behaviour C_LIO_LIChildrens behavioural data did not show evidence for attentional enhancement for multisensory objects, but 9-year-olds EEG topographic patterns elicited by multisensory vs. purely visual distractors differed reliably C_LIO_LITraditional visual attentional event-related potential (ERP) analyses, such as the N2pc, did not detect attentional enhancement for multisensory objects in adults, and visual or multisensory attention in children C_LIO_LIMultivariate analyses of ERPs, such as electrical neuroimaging, are more sensitive to the change of attentional control processes over development C_LI

neuroscience↗

bioRxiv2019

Selective attention to sound features mediates cross-modal activation of visual cortices

Contemporary schemas of brain organization now include multisensory processes both in low-level cortices as well as at early stages of stimulus processing. Evidence has also accumulated showing that unisensory stimulus processing can result in cross-modal effects. For example, task-irrelevant and lateralized sounds can activate visual cortices; a phenomenon referred to as the auditory-evoked contralateral occipital positivity (ACOP). Some claim this is an example of automatic attentional capture in visual cortices. Other results, however, indicate that context may play a determinant role. Here, we investigated whether selective attention to spatial features of sounds is a determining factor in eliciting the ACOP. We recorded high-density auditory evoked potentials (AEPs) while participants selectively attended and discriminated sounds according to four possible stimulus attributes: location, pitch, speaker identity or syllable. Sound acoustics were held constant, and their location was always equiprobable (50% left, 50% right). The only manipulation was to which sound dimension participants attended. We analysed the AEP data from healthy participants within an electrical neuroimaging framework. The presence of sound-elicited activations of visual cortices depended on the to-be-discriminated, goal-based dimension. The ACOP was elicited only when participants were required to discriminate sound location, but not when they attended to any of the non-spatial features. These results provide a further indication that the ACOP is not automatic. Moreover, our findings showcase the interplay between task-relevance and spatial (un)predictability in determining the presence of the cross-modal activation of visual cortices.

neuroscience↗