Biology subjects

Leleu, A.

Publications and source records attributed to Leleu, A..

4 recordsLinked to original sources

bioRxiv2024

Olfactory facilitation of visual categorization in the 4-month-old brain depends on visual demand

To navigate their environment, infants rely on intersensory facilitation when unisensory perceptual demand is high, a principle known as inverse effectiveness. Given that this principle was mainly documented in the context of audiovisual stimulations, here we aim to determine whether it applies to olfactory-to-visual facilitation. We build on previous evidence that the mothers body odor facilitates face categorization in the 4-month-old brain, and investigate whether this effect depends on visual demand. Scalp electroencephalogram (EEG) was recorded in 2 groups of 4-month-old infants while they watched 6-Hz streams of visual stimuli with faces displayed every 6th stimulus to tag a face-selective response at 1 Hz. We used variable natural stimuli in one group (Nat Group), while stimuli were simplified in the other group (Simp Group) to reduce perceptual categorization demand. During visual stimulation, infants were alternatively exposed to their mothers vs. a baseline odor. For both groups, we found an occipito-temporal face-selective response, but with a larger amplitude for the simplified stimuli, reflecting less demanding visual categorization. Importantly, the mothers body odor enhances the response to natural, but not to simplified, face stimuli, indicating that maternal odor improves face categorization when it is most demanding for the 4-month-old brain. Overall, this study demonstrates that the inverse effectiveness of intersensory facilitation applies to the sense of smell during early perceptual development. Highlights- Intersensory facilitation is a function of unisensory perceptual demand in infants (inverse effectiveness). - This inverse relation between multisensory and unisensory perception has been mainly documented using audiovisual stimulations. - Here we show that olfactory-to-visual facilitation depends on visual demand in 4-month-old infants. - The inverse effectiveness of intersensory facilitation during early perceptual development applies to the sense of smell.

neuroscience↗

bioRxiv2023

Olfactory-to-visual facilitation in the infant brain declines gradually from 4 to 12 months

During infant development, intersensory facilitation declines gradually as unisensory perception improves. However, this developmental trade-off has been mainly investigated using audiovisual stimulations. Here, fifty 4- to 12-month-old infants were tested to determine whether the facilitating effect of their mothers body odor on neural face categorization, as previously observed at 4 months, decreases with age. In a baseline odor context, results revealed a face-selective electroencephalographic (EEG) response that increases and changes qualitatively between 4 and 12 months, marking improved face categorization. At the same time, the benefit of adding maternal odor fades gradually with age, indicating an inverse relation with the strength of the sole visual response, and generalizing to olfactory-visual interactions previous evidence from the audiovisual domain.

neuroscience↗

bioRxiv2021

Smell what you hardly see: Odors assist categorization in the human visual cortex

Visual categorization is the brain ability to rapidly and automatically respond to widely variable visual inputs in a category-selective manner (i.e., distinct responses between categories and similar responses within categories). Whether category-selective neural responses are purely visual or can be influenced by other sensory modalities remains unclear. Here, we test whether odors modulate visual categorization, expecting that odors facilitate the neural categorization of congruent visual objects, especially when the visual category is ambiguous. Scalp electroencephalogram (EEG) was recorded while natural images depicting various objects were displayed in rapid 12-Hz streams (i.e., 12 images / second) and variable exemplars of a target category (either human faces, cars, or facelike objects in dedicated sequences) were interleaved every 9th stimulus to tag category-selective responses at 12/9 = 1.33 Hz in the EEG frequency spectrum. During visual stimulation, participants (N = 26) were implicitly exposed to odor contexts (either body, gasoline or baseline odors) and performed an orthogonal cross-detection task. We identify clear category-selective responses to every category over the occipito-temporal cortex, with the largest response for human faces and the lowest for facelike objects. Critically, body odor boosts the response to the ambiguous facelike objects (i.e., either perceived as nonface objects or faces) over the right hemisphere, especially for participants reporting their presence post-stimulation. By contrast, odors do not significantly modulate other category-selective responses, nor the general visual response recorded at 12 Hz, revealing a specific influence on the categorization of congruent ambiguous stimuli. Overall, these findings support the view that the brain actively uses cues from the different senses to readily categorize visual inputs, and that olfaction, which is generally considered as poorly functional in humans, is well placed to disambiguate visual information.

neuroscience↗

bioRxiv2021

Rapid neural categorization of facelike objects predicts the perceptual awareness of a face (face pareidolia)

The human brain rapidly and automatically categorizes faces vs. other visual objects. However, whether face-selective neural activity predicts the subjective experience of a face - perceptual awareness - is debated. To clarify this issue, here we use face pareidolia, i.e., the illusory perception of a face, as a proxy to relate the neural categorization of a variety of facelike objects to conscious face perception. In Experiment 1, scalp electroencephalogram (EEG) is recorded while pictures of human faces or facelike objects - in different stimulation sequences - are interleaved every second (i.e., at 1 Hz) in a rapid 6-Hz train of natural images of nonface objects. Participants do not perform any explicit face categorization task during stimulation, and report whether they perceived illusory faces post-stimulation. A robust categorization response to facelike objects is identified at 1 Hz and harmonics in the EEG frequency spectrum with a facelike occipito-temporal topography. Across all individuals, the facelike categorization response is of about 20% of the response to human faces, but more strongly right-lateralized. Critically, its amplitude is much larger in participants who report having perceived illusory faces. In Experiment 2, facelike or matched nonface objects from the same categories appear at 1 Hz in sequences of nonface objects presented at variable stimulation rates (60 Hz to 12 Hz) and participants explicitly report after each sequence whether they perceived illusory faces. The facelike categorization response already emerges at the shortest stimulus duration (i.e., 17 ms at 60 Hz) and predicts the behavioral report of conscious perception. Strikingly, neural facelike-selectivity emerges exclusively when participants report illusory faces. Collectively, these experiments characterize a neural signature of face pareidolia in the context of rapid categorization, supporting the view that face-selective brain activity reliably predicts the subjective experience of a face from a single glance at a variety of stimuli. Highlights- EEG frequency-tagging measures the rapid categorization of facelike objects - Facelike objects elicit a facelike neural categorization response - Neural face categorization predicts conscious face perception across variable inputs

neuroscience↗