The Effect of Motion Direction and Eccentricity on Vection, VR Sickness and Head Movements in Virtual Reality

Virtual Reality (VR) experienced through head-mounted displays often leads to vection, discomfort and sway in the user. This study investigated the effect of motion direction and eccentricity on these three phenomena using optic flow patterns displayed using the Valve Index. Visual motion stimuli were presented in the centre, periphery or far periphery and moved either in depth (back and forth) or laterally (left and right). Overall vection was stronger for motion in depth compared to lateral motion. Additionally, eccentricity primarily affected stimuli moving in depth with stronger vection for more peripherally presented motion patterns compared to more central ones. Motion direction affected the various aspects of VR sickness differently and modulated the effect of eccentricity on VR sickness. For stimuli moving in depth far peripheral presentation caused more discomfort, whereas for lateral motion the central stimuli caused more discomfort. Stimuli moving in depth led to more head movements in the anterior–posterior direction when the entire visual field was stimulated. Observers demonstrated more head movements in the anterior–posterior direction compared to the medio-lateral direction throughout the entire experiment independent of motion direction or eccentricity of the presented moving stimulus. Head movements were elicited on the same plane as the moving stimulus only for stimuli moving in depth covering the entire visual field. A correlation showed a positive relationship between dizziness and vection duration and between general discomfort and sway. Identifying where in the visual field motion presented to an individual causes the least amount of VR sickness without losing vection and presence can guide development for Virtual Reality games, training and treatment programmes.

No Evidence for a Single Oscillator Underlying Discrete Visual Percepts

Theories of perception based on discrete sampling posit that visual consciousness is reconstructed based on snapshot-like perceptual moments, as opposed to being updated continuously. According to a model proposed by Schneider (2018), discrete sampling can explain both the flash-lag and the Fröhlich illusion, whereby a lag in the conscious updating of a moving stimulus alters its perceived spatial location in comparison to a stationary stimulus. The alpha-band frequency, which is associated with phasic modulation of stimulus detection and the temporal resolution of perception, has been proposed to reflect the duration of perceptual moments. The goal of this study was to determine whether a single oscillator (e.g., alpha) is underlying the duration of perceptual moments, which would predict that the point of subjective equality (PSE) in the flash-lag and Fröhlich illusions are positively correlated across individuals. Although our displays induced robust flash-lag and Fröhlich effects, virtually zero correlation was seen between the PSE in the two illusions, indicating that the illusion magnitudes are unrelated across observers. These findings suggest that, if discrete sampling theory is true, these illusory percepts either rely on different oscillatory frequencies or not on oscillations at all. Alternatively, discrete sampling may not be the mechanism underlying these two motion illusions or our methods were ill-suited to test the theory.

Pinna-Imitating Microphone Directionality Improves Sound Localization and Discrimination in Bilateral Cochlear Implant Users

ObjectivesTo compare the sound-source localization, discrimination and tracking performance of bilateral cochlear implant users with omnidirectional (OMNI) and pinna-imitating (PI) microphone directionality modes.DesignTwelve experienced bilateral cochlear implant users participated in the study. Their audio processors were fitted with two different programs featuring either the OMNI or PI mode. Each subject performed static and dynamic sound field spatial hearing tests in the horizontal plane. The static tests consisted of an absolute sound localization test and a minimum audible angle (MAA) test, which was measured at 8 azimuth directions. Dynamic sound tracking ability was evaluated by the subject correctly indicating the direction of a moving stimulus along two circular paths around the subject.ResultsPI mode led to statistically significant sound localization and discrimination improvements. For static sound localization, the greatest benefit was a reduction in the number of front-back confusions. The front-back confusion rate was reduced from 47% with OMNI mode to 35% with PI mode (p = 0.03). The ability to discriminate sound sources at the sides was only possible with PI mode. The MAA value for the sides decreased from a 75.5 to a 37.7-degree angle when PI mode was used (p < 0.001). Furthermore, a non-significant trend towards an improvement in the ability to track sound sources was observed for both trajectories tested (p = 0.34 and p = 0.27).ConclusionsOur results demonstrate that PI mode can lead to improved spatial hearing performance in bilateral cochlear implant users, mainly as a consequence of improved front-back discrimination with PI mode.

Laterality of Eye Use by Bottlenose (Tursiops truncatus) and Rough-Toothed (Steno bredanensis) Dolphins While Viewing Predictable and Unpredictable Stimuli

Laterality of eye use has been increasingly studied in cetaceans. Research supports that many cetacean species keep prey on the right side while feeding and preferentially view unfamiliar objects with the right eye. In contrast, the left eye has been used more by calves while in close proximity to their mothers. Despite some discrepancies across and within species, laterality of eye use generally indicates functional specialization of brain hemispheres in cetaceans. The present study aimed to examine laterality of eye use in bottlenose dolphins (Tursiops truncatus) and rough-toothed dolphins (Steno bredanensis) under managed care. Subjects were video-recorded through an underwater window while viewing two different stimuli, one predictable and static and the other unpredictable and moving. Bottlenose dolphins displayed an overall right-eye preference, especially while viewing the unpredictable, moving stimulus. Rough-toothed dolphins did not display eye preference while viewing stimuli. No significant correlations between degree of laterality and behavioral interest in the stimuli were found. Only for bottlenose dolphins were the degree of laterality and curiosity ratings correlated. This study extends research on cetacean lateralization to a species not extensively examined and to stimuli that varied in movement and degree of predictability. Further research is needed to make conclusions regarding lateralization in cetaceans.

Motion Triggers Indefinite Stoppage Against Binocular Rivalry

This article provides evidence that high-speed high-information visual stimulus is able to indefinitely dominate the visual awareness; at speed of 21 degrees/second. Greater speeds emphasize greater dominance duration for the motion stimulus, however, at 21 degrees/second the moving stimulus dominates the visual awareness exclusively and indefinitely. Astonishingly, no room for mixed precepts had been reported by the human subjects at that speed, as if, it’s the ultimate domination.

Illusory changes in the perceived speed of motion derived from proprioception and touch

In vision, the perceived velocity of a moving stimulus differs depending on whether we pursue it with the eyes or not: A stimulus moving across the retina with the eyes stationary is perceived as being faster compared with a stimulus of the same physical speed that the observer pursues with the eyes, while its retinal motion is zero. This effect is known as the Aubert–Fleischl phenomenon. Here, we describe an analog phenomenon in touch. We asked participants to estimate the speed of a moving stimulus either from tactile motion only (i.e., motion across the skin), while keeping the hand world stationary, or from kinesthesia only by tracking the stimulus with a guided arm movement, such that the tactile motion on the finger was zero (i.e., only finger motion but no movement across the skin). Participants overestimated the velocity of the stimulus determined from tactile motion compared with kinesthesia in analogy with the visual Aubert–Fleischl phenomenon. In two follow-up experiments, we manipulated the stimulus noise by changing the texture of the touched surface. Similarly to the visual phenomenon, this significantly affected the strength of the illusion. This study supports the hypothesis of shared computations for motion processing between vision and touch. NEW & NOTEWORTHY In vision, the perceived velocity of a moving stimulus is different depending on whether we pursue it with the eyes or not, an effect known as the Aubert–Fleischl phenomenon. We describe an analog phenomenon in touch. We asked participants to estimate the speed of a moving stimulus either from tactile motion or by pursuing it with the hand. Participants overestimated the stimulus velocity measured from tactile motion compared with kinesthesia, in analogy with the visual Aubert–Fleischl phenomenon.

Delta phase resets mediate non-rhythmic temporal prediction

The phase of neural oscillatory activity aligns to the predicted onset of upcoming stimulation. Whether such phase alignments represent phase resets of underlying neural oscillations or just rhythmically evoked activity, and whether they can be observed in a rhythm-free visual context, however, remains unclear. Here, we recorded the magnetoencephalogram while participants were engaged in a temporal prediction task judging the visual or tactile reappearance of a uniformly moving stimulus. The prediction conditions were contrasted with a control condition to dissociate phase adjustments of neural oscillations from stimulus-driven activity. We observed stronger delta band inter-trial phase consistency (ITPC) in a network of sensory, parietal and frontal brain areas, but no power increase reflecting stimulus-driven or prediction-related processes. Delta ITPC further correlated with prediction performance in the cerebellum and visual cortex. Our results provide evidence that phase alignments of low-frequency neural oscillations underlie temporal predictions in a non-rhythmic visual and crossmodal context.

The direction after-effect is a global motion phenomenon

Prior experience influences visual perception. For example, extended viewing of a moving stimulus results in the misperception of a subsequent stimulus's motion direction—the direction after-effect (DAE). There has been an ongoing debate regarding the locus of the neural mechanisms underlying the DAE. We know the mechanisms are cortical, but there is uncertainty about where in the visual cortex they are located—at relatively early local motion processing stages, or at later global motion stages. We used a unikinetic plaid as an adapting stimulus, then measured the DAE experienced with a drifting random dot test stimulus. A unikinetic plaid comprises a static grating superimposed on a drifting grating of a different orientation. Observers cannot see the true motion direction of the moving component; instead they see pattern motion running parallel to the static component. The pattern motion of unikinetic plaids is encoded at the global processing level—specifically, in cortical areas MT and MST—and the local motion component is encoded earlier. We measured the direction after-effect as a function of the plaid's local and pattern motion directions. The DAE was induced by the plaid's pattern motion, but not by its component motion. This points to the neural mechanisms underlying the DAE being located at the global motion processing level, and no earlier than area MT.

Differences in the Magnitude of Representational Momentum Between School-Aged Children and Adults as a Function of Experimental Task

Representational momentum (RM) is the phenomenon that occurs when an object moves and then disappears, and the recalled final position of the object shifts in the direction of its motion. Some previous findings indicate that the magnitude of RM in early childhood is comparable to that in adulthood, whereas other findings suggest that the magnitude of RM is significantly greater in childhood than in adulthood. We examined whether the inconsistencies between previous studies could be explained by differences in the experimental tasks used in these studies. Futterweit and Beilin used a same-different judgment between the position where a moving stimulus disappeared and where a comparison stimulus reappeared (judging task), whereas Hubbard et al. used a task wherein a computer mouse cursor pointed to the position where the moving stimulus disappeared (pointing task). Three age groups ( M = 7.4, 10.7, and 22.1 years, respectively) participated in both the judging and pointing tasks in the current study. A multivariate analysis of variance with the magnitudes of RM in each task as dependent variables revealed a significant main effect for age. A one-way analysis of variance performed for each of the judging and pointing tasks also indicated a significant main effect of age. However, post hoc multiple comparisons detected a significant age effect only for the pointing task. The inconsistency between the judging and pointing tasks was discussed related to the distinct effect size of the age difference in the magnitude of RM between the two tasks.