Biology subjects

Carmel, D.

Publications and source records attributed to Carmel, D..

3 recordsLinked to original sources

bioRxiv2025

Effective connectivity reveals a shift to left-hemisphere dominance for spatial attention with diminishing arousal

Spatial attention becomes biased toward the right side of space when alertness wanes, but the neural mechanisms underlying this shift remain unresolved. Competing theories propose that spatial attention depends either on a dominant right hemisphere, interhemispheric competition, or interactions between dorsal and ventral attention networks. Here, we used drowsiness as a model to investigate how diminishing alertness reshapes the cortical dynamics supporting auditory spatial attention. Thirty healthy participants completed a lateralised auditory localisation task while high-density EEG was recorded during wakefulness and drowsiness. Behaviourally, drowsiness selectively impaired localisation accuracy for left-sided stimuli, replicating the typical neglect-like rightward attentional bias observed with lower arousal in healthy people, and pathological attention deficits in brain injury patients. Using Dynamic Causal Modelling and Parametric Empirical Bayes, we identified a striking reconfiguration of effective cortico-cortical connectivity across arousal states. During wakefulness, spatial attention was characterised by reciprocal interhemispheric signalling between inferior frontal regions, consistent with balanced bilateral coordination. During drowsiness, this pattern shifted toward reduced right frontoparietal connectivity together with increased left-hemispheric parietofrontal connectivity. These findings suggest that waning alertness destabilises balanced interhemispheric control and allows left-hemispheric processing to dominate attentional processing. Rather than fully supporting existing theories of spatial attention, our results point toward a hybrid mechanism in which neglect-like spatial bias emerges from the interaction between right-hemispheric dysconnection and left-hemispheric dominance under low arousal. Diminishing alertness reshapes interhemispheric coordination rather than simply reducing right-hemisphere function.

neuroscience↗

bioRxiv2021

Minimal required exposures reveal the primacy of awareness in human face perception

Human vision can detect a single photon, but the minimal exposure required to extract meaning from stimulation remains unknown. This requirement cannot be cha racterised by stimulus energy, because the system is differentially sensitive to attributes defined by configuration rather than physical amplitude. Determining minimal exposure durations required for processing various stimulus attributes can thus reveal the systems priorities. Using a tachistoscope enabling arbitrarily brief displays, we established minimal durations for processing human faces, a stimulus category whose perception is associated with several well-characterised behavioural and neural markers. Neural and psychophysical measures showed a sequence of distinct minimal exposures for stimulation detection, object-level detection, face-specific processing, and emotion-specific processing. Resolving ongoing debates, face orientation affected minimal exposure but emotional expression did not. Awareness emerged with detection, showing no evidence of subliminal perception. These findings inform theories of visual processing and awareness, elucidating the information to which the visual system is attuned.

neuroscience↗

bioRxiv2018

Affective flexibility without perceptual awareness

In an ever-changing environment, survival depends on learning which stimuli represent threat, and also on updating such associations when circumstances shift. Humans can acquire physiological responses to threat-associated stimuli even when they are unaware of them, but the role of awareness in updating threat contingencies remains unknown. This complex process - generating novel responses while simultaneously suppressing learned ones - relies on distinct neural mechanisms from initial learning, and has only been shown with awareness. Can it occur unconsciously? Here we show that it can. Participants underwent classical threat conditioning to visual stimuli that were suppressed from their awareness. One of two images was paired with an electric shock; halfway through the experiment, contingencies were reversed and the shock was paired with the other image. We found that physiological responses reflected changes in stimulus-threat pairings independently of stimulus awareness, demonstrating the sophistication of unconscious affective flexibility.

neuroscience↗