Biology subjects

Shafiei, M.

Publications and source records attributed to Shafiei, M..

4 recordsLinked to original sources

bioRxiv2026

Behavioral evidence challenges species-specific ocular morphology as a primary constraint on human gaze-following

Previous research suggests that humans are extremely sensitive to object-directed eye gaze, which effectively guides their attention toward objects of shared interest. This contrasts with non-human primates, who typically require much more salient eye-gaze cues to achieve comparable attentional orienting. However, it remains unclear whether cross-species differences in ocular morphology account for this performance gap. To address this question, we examined humans covert shifts of spatial attention in response to eye-gaze cues provided by either realistic human or rhesus monkey head avatars. Target detection was reliably enhanced on gaze-congruent compared to gaze-incongruent trials, with comparable gaze-cueing effects for both avatar types, despite the fact that monkey eyes lack many of the conspicuous features characteristic of human eyes. Hence, eye morphology alone does not substantially modulate gaze-driven attentional orienting in humans, whereas humans reliable use of monkey eye-gaze cues highlights a clear species difference in perceptual sensitivity to eye gaze signals. Significance StatementEye-gaze-mediated attentional orienting is a conserved ability across primates, yet sensitivity to subtle eye-gaze cues may differ between species. Here, we provide empirical evidence that humans exhibit a quantitatively greater capacity than non-human primates to follow subtle eye-gaze cues. Importantly, we showed that this difference cannot be attributed to species-specific ocular morphology as human participants showed robust and comparable reflexive attentional orienting to both human and rhesus monkey eye-gaze cues. This is striking given the pronounced differences in ocular morphology and coloration/contrast between the two species. These findings suggest that cross-species diversity in extracting spatial information from eye-gaze cues likely reflects differences in perceptual sensitivity rather than bottom-up constraints imposed by species-specific ocular morphology.

neuroscience↗

bioRxiv2025

Rhesus monkeys use both eye and head gaze to reallocate covert spatial attention facilitating visual perception

Non-verbal cues, particularly eye gaze, significantly shape human social interactions. Although non-human primates reliably follow head gaze, their capacity to use eye gaze alone for inferring the others focus of attention remains debated. We investigated this question using a realistic rhesus monkey head avatar that directed its gaze toward one of two LEDs (left or right), employing either eye movements alone or combined eye and head movements. After a randomly chosen interval (ranging 50-400 ms) from gaze presentation, one LED transiently increased its luminance to near-threshold levels. Rhesus monkeys were trained to detect and report this luminance change via a saccade to the corresponding LED, independent of the avatars gaze direction, to receive rewards. Our results showed that head-gaze cues robustly directed covert attention toward gaze-congruent targets with short delays, indicative of reflex-like, stimulus-driven orienting. In contrast, eye gaze alone, at comparable amplitudes, did not affect attention shifts. However, increasing the avatars size and eye-gaze amplitude, simulating a close-range interaction, made eye gaze cues effective in guiding attention. These findings demonstrate that rhesus monkeys possess the capacity to use eye-gaze cues to determine conspecifics attentional targets, and validate and underscore the utility of 3D animal models as powerful tools for generating realistic yet precisely controlled stimuli. Our study supports the idea that eye-gaze following is not uniquely human but is an evolutionarily ancient ability, likely shared across Old World monkeys and apes which diverged more than 30 million years ago.

animal behavior and cognition↗

bioRxiv2024

Implied motion guides neither gaze following nor intention attribution

The "gaze beam hypothesis (GBH)" of gaze following posits that the others eyes emit imaginary beams of moving energy travelling to the others object of attention (1), drawing the observers attention to the same object. This idea was initially supported by behavioral experiments showing a motion aftereffect (MAE), indicated by longer reaction times in detecting motion direction after viewing a cartoon face looking at an object in the same direction (2). However, this effect could also be expected if the observer used gaze direction to assume an intentional link between the looker and the object, envisioning directed actions toward the latter (3). To critically compare the two hypotheses, we tested whether an MAE could be induced by having human subjects detect motion direction after viewing various cue images, designed to differentiate the explanatory power of the two. Cues either suggested a connection between an agent and an object through the agents gaze or an object-oriented intention by the presence of equipment in the agents hand, without the agent directly looking at the object. Using Bayesian statistics, our findings provided strong evidence against both hypotheses at the population level, as reaction time modulations did not align with the MAE, leading us to reject motion adaptation as the underlying mechanism for gaze following but also intention attribution. As on an individual level we observed highly diverse effects, with some compatible with one or the other hypothesis, we assume that individual subjects may resort to different perceptual strategies based on different scene interpretations.

neuroscience↗

bioRxiv2023

Acute effects of subanesthetic ketamine on cerebrovascular hemodynamics in humans: A TD-fNIRS neuroimaging study

Quantifying neural activity in natural conditions (i.e. conditions comparable to the standard clinical patient experience) during the administration of psychedelics may further our scientific understanding of the effects and mechanisms of action. This data may facilitate the discovery of novel biomarkers enabling more personalized treatments and improved patient outcomes. In this single-blind, placebo-controlled study with a non-randomized design, we use time-domain functional near-infrared spectroscopy (TD-fNIRS) to measure acute brain dynamics after intramuscular subanesthetic ketamine (0.75 mg/kg) and placebo (saline) administration in healthy participants (n = 15, 8 females, 7 males, age 32.4 {+/-} 7.5 years) in a clinical setting. We found that the ketamine administration caused an altered state of consciousness and changes in systemic physiology (e.g. increase in pulse rate and electrodermal activity). Furthermore, ketamine led to a brain-wide reduction in the fractional amplitude of low frequency fluctuations (fALFF), and a decrease in the global brain connectivity of the prefrontal region. Lastly, we provide preliminary evidence that a combination of neural and physiological metrics may serve as predictors of subjective mystical experiences and reductions in depressive symptomatology. Overall, our studies demonstrated the successful application of fNIRS neuroimaging to study the physiological effects of the psychoactive substance ketamine and can be regarded as an important step toward larger scale clinical fNIRS studies that can quantify the impact of psychedelics on the brain in standard clinical settings.

neuroscience↗