Eye pupil signals life motion perception.

The ability to readily detect and recognize biological motion (BM) is fundamental to survival and interpersonal communication. However, perception of BM is strongly disrupted when it is shown upside down. This well-known inversion effect is proposed to be caused by a life motion detection mechanism highly tuned to gravity-compatible motion cues. In the current study, we assessed the inversion effect in BM perception using a no-report pupillometry. We found that the pupil size was significantly enlarged when observers viewed upright BMs (gravity-compatible) compared with the inverted counterparts (gravity-incompatible). Importantly, such an effect critically depended on the dynamic biological characteristics, and could be extended to local feet motion signals. These findings demonstrate that the eye pupil can signal gravity-dependent life motion perception. More importantly, with the convenience, objectivity, and noninvasiveness of pupillometry, the current study paves the way for the potential application of pupillary responses in detecting the deficiency of life motion perception in individuals with socio-cognitive disorders.

Linear integration of multisensory signals in the pupil.

The pupil of the eye responds to various salient signals from different modalities, but there is no consensus on how these pupillary responses are integrated when multiple signals appear simultaneously. Both linear and nonlinear integration have been found previously. The current study aimed to reexamine the nature of pupillary integration, and specifically focused on the early, transient pupillary responses due to its close relationship with orienting. To separate the early pupillary responses out of the pupil time series, we adopted a pupil oscillation paradigm in which sensory stimuli were periodically presented. The simulation analysis confirmed that the amplitude of the pupil oscillation, induced by stimuli repeatedly presented at relatively high rates, can precisely reflect the early, transient pupillary responses without involving the late and sustained pupillary responses. The experimental results then showed that the amplitude of pupil oscillation induced by a series of simultaneous audiovisual stimuli equaled to a linear summation of the oscillatory amplitudes when unisensory stimuli were presented alone. Moreover, the tonic arousal levels, indicated by the baseline pupil size, cannot shift the summation from linear to nonlinear. These findings together support the additive nature of multisensory pupillary integration for the early, orienting-related pupillary responses. The additive nature of pupillary integration further implies that multiple pupillary responses may be independent of each other, irrespective of their potential cognitive and neural drivers.

Rapid Unconscious Acquisition of Conditioned Fear with Low-Spatial-Frequency but Emotionally Neutral Stimuli.

It has long been proposed that emotionally "prepared" (i.e., fear-related) stimuli are privileged in the unconscious acquisition of conditioned fear. However, as fear processing is suggested to highly depend on the coarse, low-spatial-frequency (LSF) components of the fear-related stimuli, it is plausible that LSF may play a unique role in the unconscious fear conditioning even with emotionally neutral stimuli. Here, we provided empirical evidence that, following classical fear conditioning, an invisible, emotionally neutral conditioned stimulus (CS+) with LSF, but not with high spatial frequency (HSF), can rapidly elicit stronger skin conductance responses (SCRs) and larger pupil diameters than its CS- counterpart. In comparison, consciously perceived emotionally neutral CS+ with LSF and HSF elicited comparable SCRs. Taken together, these results support that the unconscious fear conditioning does not necessarily entail emotionally prepared stimuli but prioritizes LSF information processing and highlight the crucial distinctions between the unconscious and the conscious fear learning. These findings not only coincide with the postulation that a rapid, spatial-frequency-dependent subcortical route is engaged in unconscious fear processing but also suggest the existence of multiple routes for conscious fear processing.

Conscious and unconscious processing of ensemble statistics oppositely modulate perceptual decision-making.

Our visual system possesses a remarkable ability to extract summary statistical information from groups of similar objects, known as ensemble perception. It remains elusive whether the processing of ensemble statistics exerts influences on our perceptual decision-making and what roles consciousness and attention play in this process. In a series of experiments, we demonstrated that the processing of ensemble statistics can exert significant modulation effects on our perceptual decision-making, which is independent of consciousness but relies on attentional resources. More intriguingly, the conscious and unconscious ensemble representations respectively induce repulsive and attractive modulation effects, with the unconscious effect susceptible to the temporal separation and the distinction between the inducers and the targets. These results not only suggest that the conscious and unconscious ensemble representations engage different visual processing mechanisms but also highlight the distinct roles of consciousness and attention in ensemble perception. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Cortical encoding of rhythmic kinematic structures in biological motion.

Biological motion (BM) perception is of great survival value to human beings. The critical characteristics of BM information lie in kinematic cues containing rhythmic structures. However, how rhythmic kinematic structures of BM are dynamically represented in the brain and contribute to visual BM processing remains largely unknown. Here, we probed this issue in three experiments using electroencephalogram (EEG). We found that neural oscillations of observers entrained to the hierarchical kinematic structures of the BM sequences (i.e., step-cycle and gait-cycle for point-light walkers). Notably, only the cortical tracking of the higher-level rhythmic structure (i.e., gait-cycle) exhibited a BM processing specificity, manifested by enhanced neural responses to upright over inverted BM stimuli. This effect could be extended to different motion types and tasks, with its strength positively correlated with the perceptual sensitivity to BM stimuli at the right temporal brain region dedicated to visual BM processing. Modeling results further suggest that the neural encoding of spatiotemporally integrative kinematic cues, in particular the opponent motions of bilateral limbs, drives the selective cortical tracking of BM information. These findings underscore the existence of a cortical mechanism that encodes periodic kinematic features of body movements, which underlies the dynamic construction of visual BM perception.

Looking more masculine among females: Spatial context modulates gender perception of face and biological motion.

Perception of visual information highly depends on spatial context. For instance, perception of a low-level visual feature, such as orientation, can be shifted away from its surrounding context, exhibiting a simultaneous contrast effect. Although previous studies have demonstrated the adaptation aftereffect of gender, a high-level visual feature, it remains largely unknown whether gender perception can also be shaped by a simultaneously presented context. In the present study, we found that the gender perception of a central face or a point-light walker was repelled away from the gender of its surrounding faces or walkers. A norm-based opponent model of lateral inhibition, which accounts for the adaptation aftereffect of high-level features, can also excellently fit the simultaneous contrast effect. But different from the reported contextual effect of low-level features, the simultaneous contrast effect of gender cannot be observed when the centre and the surrounding stimuli are from different categories, or when the surrounding stimuli are suppressed from awareness. These findings on one hand reveal a resemblance between the simultaneous contrast effect and the adaptation aftereffect of high-level features, on the other hand highlight different biological mechanisms underlying the contextual effects of low- and high-level visual features.

Erratum to "Gravity-Dependent Animacy Perception in Zebrafish".

[This corrects the article DOI: 10.34133/2022/9829016.].

Gravity-Dependent Animacy Perception in Zebrafish.

Biological motion (BM), depicted by a handful of point lights attached to the major joints, conveys rich animacy information, which is significantly disrupted if BM is shown upside down. This well-known inversion effect in BM perception is conserved in terrestrial vertebrates and is presumably a manifestation of an evolutionarily endowed perceptual filter (i.e., life motion detector) tuned to gravity-compatible BM. However, it remains unknown whether aquatic animals, living in a completely different environment from terrestrial animals, perceive BM in a gravity-dependent manner. Here, taking advantage of their typical shoaling behaviors, we used zebrafish as a model animal to examine the ability of teleosts to discriminate between upright (gravity-compatible) and inverted (gravity-incompatible) BM signals. We recorded their swimming trajectories and quantified their preference based on dwelling time and head orientation. The results obtained from three experiments consistently showed that zebrafish spent significantly more time swimming in proximity to and orienting towards the upright BM relative to the inverted BM or other gravity-incompatible point-light stimuli (i.e., the non-BM). More intriguingly, when the recorded point-light video clips of fish were directly compared with those of human walkers and pigeons, we could identify a unique and consistent pattern of accelerating movements in the vertical (gravity) direction. These findings, to our knowledge, demonstrate for the first time the inversion effect in BM perception in simple aquatic vertebrates and suggest that the evolutionary origin of gravity-dependent BM processing may be traced back to ancient aquatic animals.

Following Other People's Footsteps: A Contextual-Attraction Effect Induced by Biological Motion.

Our visual system is bombarded with numerous social interactions that form intangible social bonds among people, as exemplified by synchronized walking in crowds. Here, we investigated whether these perceived social bonds implicitly intrude on visual perception and induce a contextual effect. Using multiple point-light walkers and a classical contextual paradigm, we tested 72 college-age adults across six experiments and found that the perceived direction of the central walker was attracted toward the direction of the surrounding walkers. The observed contextual-attraction effect occurred even when the surrounding walkers differed from the central walker in gender and walking speed but disappeared when they were asynchronously presented or replaced by inanimate motion. Strikingly, this contextual-attraction effect partially persisted in the context of local motion rather than static figures. These findings, in contrast to the typical contextual-repulsion effect, lend support for the distinctiveness of perceived social bonds on contextual modulation and suggest a specialized contextual mechanism tuned to social factors.

Social attention triggered by eye gaze and walking direction is resistant to temporal decay.

The attentional orienting induced by social cues, such as eye gaze and walking direction of biological motion, plays a vital role in human survival and interpersonal interactions. It has long been debated whether this indispensable ability is unique and intrinsically distinct from nonsocial attention. In the current study, we characterized the temporal profiles of the attentional orienting triggered by social cues (i.e., eye gaze and walking direction) and compared them with those induced by nonsocial cues (i.e., arrows) and exogenous cues using a covert orienting task. We calculated the attentional cuing effects in the early and the late periods of the task and further carried out a time course analysis to characterize their dynamic changes over trials. Whereas the cuing effect induced by nonsocial cues exhibited a significant trend of temporal decay, the cuing effects induced by the two different social cues were similar and remained stable throughout the task, resembling that induced by reflexive exogenous cues. These results clearly demonstrate that the socially coordinated attentional orienting is a highly reflexive and temporally stable response, which is less susceptible to top-down cognitive control and substantially distinguished from the attentional orienting induced by nonsocial cues. These findings extend our understandings of the distinction between social and nonsocial attention and further substantiate the specificity of social attentional orienting from a temporal-stability perspective. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Multisensory signals inhibit pupillary light reflex: Evidence from pupil oscillation.

Multisensory integration, which enhances stimulus saliency at the early stage of the processing hierarchy, has been recently shown to produce a larger pupil size than its unisensory constituents. Theoretically, any modulation on pupil size ought to be associated with the sympathetic and parasympathetic pathways that are sensitive to light. But it remains poorly understood how the pupillary light reflex is changed in a multisensory context. The present study evoked an oscillation of the pupillary light reflex by periodically changing the luminance of a visual stimulus at 1.25 Hz. It was found that such induced pupil size oscillation was substantially attenuated when the bright but not the dark phase of the visual flicker was periodically and synchronously presented with a burst of tones. This inhibition effect persisted when the visual flicker was task-irrelevant and out of attentional focus, but disappeared when the visual flicker was moved from the central field to the periphery. These findings not only offer a comprehensive characterization of the multisensory impact on pupil response to light, but also provide valuable clues about the individual contributions of the sympathetic and parasympathetic pathways to multisensory modulation of pupil size.

Attentional focus modulates automatic finger-tapping movements.

The majority of human behaviors are composed of automatic movements (e.g., walking or finger-tapping) which are learned during nurturing and can be performed simultaneously without interfering with other tasks. One critical and yet to be examined assumption is that the attention system has the innate capacity to modulate automatic movements. The present study tests this assumption. Setting no deliberate goals for movement, we required sixteen participants to perform personalized and well-practiced finger-tapping movements in three experiments while focusing their attention on either different component fingers or away from movements. Using cutting-edge pose estimation techniques to quantify tapping trajectory, we showed that attention to movement can disrupt movement automaticity, as indicated by decreased inter-finger and inter-trial temporal coherence; facilitate the attended and inhibit the unattended movements in terms of tapping amplitude; and re-organize the action sequence into distinctive patterns according to the focus of attention. These findings demonstrate compelling evidence that attention can modulate automatic movements and provide an empirical foundation for theories based on such modulation in controlling human behavior.

Perception of social interaction compresses subjective duration in an oxytocin-dependent manner.

Communication through body gestures permeates our daily life. Efficient perception of the message therein reflects one's social cognitive competency. Here we report that such competency is manifested temporally as shortened subjective duration of social interactions: motion sequences showing agents acting communicatively are perceived to be significantly shorter in duration as compared with those acting noncommunicatively. The strength of this effect is negatively correlated with one's autistic-like tendency. Critically, intranasal oxytocin administration restores the temporal compression effect in socially less proficient individuals, whereas the administration of atosiban, a competitive antagonist of oxytocin, diminishes the effect in socially proficient individuals. These findings indicate that perceived time, rather than being a faithful representation of physical time, is highly idiosyncratic and ingrained with one's personality trait. Moreover, they suggest that oxytocin is involved in mediating time perception of social interaction, further supporting the role of oxytocin in human social cognition.

Dynamic tilt illusion induced by continuous contextual orientation alternations.

In the classic tilt illusion, the perceived orientation of a center patch is shifted away from its oriented context. Additionally, a stronger illusion effect is yielded when the center patch is simultaneously rather than asynchronously presented with a constant context for a shorter duration. However, little is known about the temporal characteristic of the tilt illusion in a reverse situation in which a constant center patch is presented throughout while the contexts change. Therefore, we continuously alternated two opposite-oriented contexts and manipulated alternate speeds to examine how the tilt illusion would build up as a function of dynamic contextual alternation. Our results revealed that dynamic alternations between leftward- and rightward-oriented contexts caused a static vertical grating at the center to apparently sway from side to side. More importantly, the apparent sway illusion was modulated by the alternate speed of the oriented contexts (up to 8-10 Hz); the quicker the alternation is, the faster and weaker the apparent sway is. Intriguingly, the temporal characteristic of the "dynamic tilt illusion" suggests that, under a varying environment, the suppressions from temporally adjacent surrounds would be chunked into discrete epochs before affecting our percept.

Subliminal Impending Collision Increases Perceived Object Size and Enhances Pupillary Light Reflex.

Fast detection of ambient danger is crucial for the survival of biological entities. Previous studies have shown that threatening information can bias human visual perception and enhance physiological reactions. It remains to be delineated whether the modulation of threat on human perceptual and physiological responses can take place below awareness. To probe this issue, we adopted visual looming stimuli and created two levels of threat by varying their motion trajectories to the observers, such that the stimuli could move in a path that either collided with the observers' heads or just nearly missed. We found that when the observers could not explicitly discriminate any difference between the collision and the near-miss stimuli, the visual stimuli on the collision course appeared larger and evoked greater pupil constrictions than those on the near-miss course. Furthermore, the magnitude of size overestimation was comparable to when the impending collision was consciously perceived. Our findings suggest that threatening information can bias human visual perception and strengthen pupil constrictions independent of conscious representation of the threat, and imply the existence of the subcortical visual pathway dedicated to automatically processing threat-related signals in humans.

Pre-stimulus beta and gamma oscillatory power predicts perceived audiovisual simultaneity.

Pre-stimulus oscillation activity in the brain continuously fluctuates, but it is correlated with subsequent behavioral and perceptual performance. Here, using fast Fourier transformation of pre-stimulus electroencephalograms, we explored how oscillatory power modulates the subsequent discrimination of perceived simultaneity from non-simultaneity in the audiovisual domain. We found that the over-scalp high beta (20-28Hz), parieto-occipital low beta (14-20Hz), and high gamma oscillations (55-80Hz) were significantly stronger before audition-then-vision sequence when they were judged as simultaneous rather than non-simultaneous. In contrast, a broad range of oscillations, mainly the beta and gamma bands over a great part of the scalp were significantly weaker before vision-then-audition sequences when they were judged as simultaneous versus non-simultaneous. Moreover, for auditory-leading sequence, pre-stimulus beta and gamma oscillatory power successfully predicted subjects' reports of simultaneity on a trial-by-trial basis, with stronger activity resulting in more simultaneous judgments. These results indicate that ongoing fluctuations of beta and gamma oscillations can modulate subsequent perceived audiovisual simultaneity, but with an opposing pattern for auditory- and visual-leading sequences.

Visual duration aftereffect is position invariant.

Adaptation to relatively long or short sensory events leads to a negative aftereffect, such that the durations of the subsequent events within a certain range appear to be contracted or expanded. The distortion in perceived duration is presumed to arise from the adaptation of duration detectors. Here, we focus on the positional sensitivity of those visual duration detectors by exploring whether the duration aftereffect may be constrained by the visual location of stimuli. We adopted two different paradigms, one that tests for transfer across visual hemifields, and the other that tests for simultaneous selectivity between visual hemifields. By employing these experimental designs, we show that the duration aftereffect strongly transfers across visual hemifields and is not contingent on them. The lack of position specificity suggests that duration detectors in the visual system may operate at a relatively later stage of sensory processing.

The aftereffect of perceived duration is contingent on auditory frequency but not visual orientation.

Recent sensory history plays a critical role in duration perception. It has been established that after adapting to a particular duration, the test durations within a certain range appear to be distorted. To explore whether the aftereffect of perceived duration can be constrained by sensory modality and stimulus feature within a modality, the current study applied the technique of simultaneous sensory adaptation, by which observers were able to simultaneously adapt to two durations defined by two different stimuli. Using both simple visual and auditory stimuli, we found that the aftereffect of perceived duration is modality specific and contingent on auditory frequency but not visual orientation of the stimulus. These results demonstrate that there are independent timers responsible for the aftereffects of perceived duration in each sensory modality. Furthermore, the timer for the auditory modality may be located at a relatively earlier stage of sensory processing than the timer for the visual modality.

Individual alerting efficiency modulates time perception.

Time perception plays a fundamental role in human perceptual and motor activities, and can be influenced by various factors, such as selective attention and arousal. However, little is known about the influence of individual alerting efficiency on perceived duration. In this study, we explored this question by running two experiments. The Attentional Networks Test was used to evaluate individual differences in alerting efficiency in each experiment. Temporal bisection (Experiment 1) and time generalization task (Experiment 2) were used to explore the participants' perception of duration. The results indicated that subjects in the high alerting efficiency group overestimated interval durations and estimated durations more accurately compared with subjects in the low alerting efficiency group. The two experiments showed that the sensitivity of time was not influenced by individual alerting efficiency. Based on previous studies and current findings, we infer that individual differences in alerting efficiency may influence time perception through modulating the latency of the attention-controlled switch and the speed of the peacemaker within the framework of the internal clock model.