Neuronal correlates of optic flow stimulation.

Ocular responses to radial optic flow and single accelerated targets in humans

A feedback control process based on self-motion perception contributes to postural stability; however, little is known about the visual modulation of postural muscles. The aim of this study was to investigate the effect of optic flow stimuli, presented full field, in the peripheral and foveal visual field, on muscular activation. Then, we assessed the correlation between optic flow, muscle activity and body sway in male and female subjects. We used surface electromyography (EMG) and stabilometry on 24 right-handed young adults. We recorded the bilateral activation of tibialis anterior, gastrocnemius medialis, biceps femoris and vastus medialis. EMG and center of pressure (COP) signals were acquired simultaneously. EMG signal amplitude was computed as root mean square normalized by baseline. We found a significant effect for muscles, gender and an interaction effect of muscle by gender (ANOVA, p < 0.001). Results showed different postural alignments in males and females. The COP spatial variability during peripheral stimuli was generally reduced. The prevalent direction of oscillation evoked by peripheral stimuli was clustered, while foveal and random stimuli induced distributed and randomized directions. Also for muscle activity, we found gender differences in the prevalent oscillation distributions evoked by optic flow. Visual stimuli always evoke an excitatory input on postural muscles, but the stimulus structure produces different postural effects. Peripheral optic flow stimuli stabilize postural sway, while random and foveal optic flow provoke larger sway variability similar to those evoked in the absence of visual stimulation.

Più mosso: Fast self-motion makes cyclic action faster in virtual reality

Optic flow neurons in area PEc integrate eye and head position signals

In humans, several neuroimaging studies have demonstrated that passive viewing of optic flow stimuli activates higher-level motion areas, like V6 and the cingulate sulcus visual area (CSv). In macaque, there are few studies on the sensitivity of V6 and CSv to egomotion compatible optic flow. The only fMRI study on this issue revealed selectivity to egomotion compatible optic flow in macaque CSv but not in V6 (Cotterau et al. Cereb Cortex 27(1):330-343, 2017, but see Fan et al. J Neurosci. 35:16303-16314, 2015). Yet, it is unknown whether monkey visual motion areas MT + and V6 display any distinctive fMRI functional profile relative to the optic flow stimulation, as it is the case for the homologous human areas (Pitzalis et al., Cereb Cortex 20(2):411-424, 2010). Here, we described the sensitivity of the monkey brain to two motion stimuli (radial rings and flow fields) originally used in humans to functionally map the motion middle temporal area MT + (Tootell et al. J Neurosci 15: 3215-3230, 1995a; Nature 375:139-141, 1995b) and the motion medial parietal area V6 (Pitzalis et al. 2010), respectively. In both animals, we found regions responding only to optic flow or radial rings stimulation, and regions responding to both stimuli. A region in the parieto-occipital sulcus (likely including V6) was one of the most highly selective area for coherently moving fields of dots, further demonstrating the power of this type of stimulation to activate V6 in both humans and monkeys. We did not find any evidence that putative macaque CSv responds to Flow Fields.

Optic flow-induced sway in anxiety disorders associated with space and motion discomfort

Robustness of perception of heading from optic flow

BackgroundThe dorsal parietal visual system plays an important role in self-motion perception and spatial cognition. It also strongly responds to visual inputs from the lower visual field. Postural control is modified in a process called sensory reweighting based on the reliability of available sensory sources. The question of whether visual stimuli presented to either the lower or upper visual field affect postural control and sensory reweighting has not been resolved. Research questionDo visual stimuli presented to the lower and upper visual fields affect postural control and sensory reweighting? MethodsTwenty-nine healthy young adults participated in the study. Four conditions (full visual field, upper visual field, lower visual field, and no optic flow condition) were simulated in a VR environment using a head-mounted display. The optic flow stimuli used were swarms of small white spheres originating from the central point of the visual field, moving radially towards the periphery, and expanding across the scene. Participants were instructed to stand quietly for 50 s under each visual condition. Using force plate signals, we measured the center of pressure (COP) signal in the horizontal plane and calculated its 95 % ellipse area, root mean square (RMS) deviations, the mean velocity, and power spectral density (PSD). ResultsOptic flow in the full and lower visual fields produced significantly smaller 95 % ellipse area and RMS of COP in the anterior-posterior direction compared to optic flow in the upper visual field. Furthermore, the PSD of the lower frequency band (0–0.3 Hz) was decreased and that of higher frequency bands (0.3–1 Hz and 1–3 Hz) was increased for the lower compared to the upper visual field. SignificanceVisual feedback affects static postural control more when presented in the lower visual field compared to the upper visual field.

Changes in neuronal responses during and after adaptation to prolonged optic flow stimulation were investigated by extracellular single-unit recording in the posteromedial lateral suprasylvian area (PMLS) of the cat. In comparison with translation stimuli, the complex optic flow patterns (radiation and rotation) produced more pronounced adaptation and after-effects by inducing larger response reduction, and altered the direction selectivity of many neurons obviously as well. Generally, the adaptation effects were direction-specific for radiation/rotation, but independent of the direction of test stimulus for translation. These results suggest that PMLS may play an important role in the perception of motion after-effects to complex optic flow fields, while the adaptation to simple translation might be generated at a relatively earlier level of the visual system.

There is a critical need to understand how aging visual systems contribute to age-related increases in vehicle accidents. We investigated the potential contribution of age-related detriments in steering based on optic flow, a source of information known to play a role in navigation control. Seventeen younger adults (mean age: 21.1 years) and thirteen older adults (mean age: 57.3 years) performed a virtual reality steering task. The virtual environment depicted movement at 19 m/s along a winding road. Participants were tasked with maintaining a central lane position while experiencing eight repetitions of each combination of optic flow density (low, medium, high), turn radius (35, 55, 75 m), and turn direction (left, right), presented in random order. All participants cut corners, but did so less on turns with rotational flow from distant landmarks and without proximal optic flow. We found no evidence of an interaction between age and optic flow density, although older adults cut corners more on all turns. An exploratory gaze analysis revealed no age-related differences in gaze behavior. The lack of age-related differences in steering or gaze behavior as a function of optic flow implies that processing of naturalistic optic flow stimuli when steering may be preserved with age.

Head direction (HD) neurons fire selectively according to head orientation in the yaw plane relative to environmental landmark cues. Head movements provoke optic field flow signals that enter the vestibular nuclei, indicating head velocity, and hence angular displacements. To test whether optic field flow alone affects the directional firing of HD neurons, rats walked about on a circular platform as a spot array was projected onto the surrounding floor-to-ceiling cylindrical black curtain. Directional responses in the anterodorsal thalamus of four rats remained stable as they moved about with the point field but in the absence of landmark cues. Then, the spherical projector was rotated about its yaw axis at 4.5°/s for ∼90 s. In 27 sessions the mean drift speed of the preferred directions (PDs) was 1.48°/s (SD=0.78°/s; range: 0.15 to 2.88°/s). Thus, optic flow stimulation entrained PDs, albeit at drift speeds slower than the field rotation. This could be due to conflicts with vestibular, motor command, and efferent copy signals. After field rotation ended, 20/27 PDs drifted back to within 45° of the initial values over several minutes, generally following the shortest path to return to the initial value. Poststimulation drifts could change speed and/or direction, with mean speeds of 0.68±0.64°/s (range 0 to 1.36°/s). Since the HD cell pathway (containing anterodorsal thalamus) is the only known projection of head direction information to entorhinal grid cells and hippocampal place cells, yaw plane optic flow signals likely influence representations in this spatial reference coordinate system for orientation and navigation.

This study investigated the effects of prolonged virtual reality (VR) optic flow exposure on standing balance, focusing on how optic flow parameters influence balance responses and the potential for habituation. While short-term responses to optic flow are well-documented, the impact of extended VR immersion (up to 60min) on balance remains poorly understood. Twenty healthy young adults were exposed to sinusoidal optic flow stimuli in a novel VR environment, with different velocities (0.1, 1, 10m/s) and frequencies (0.125, 0.25, 0.5Hz). Balance responses were assessed using a force plate to measure anteroposterior centre of pressure (CoP) velocity (AP-Vel) and mean power frequency (MPF). VR optic flow elicited significantly greater AP-Vel (P < 0.0001) and MPF (P < 0.0001) compared to non-VR eyes open conditions, with higher optic flow velocities and frequencies inducing greater balance responses (AP-Vel: P = 0.0322; MPF: P = 0.0027). Despite prolonged VR exposure, no evidence of habituation was observed within 90-second trials (P > 0.2110) or over the 40-60-minute experiment (P > 0.6724). Participants reported increased physical (P = 0.0010) and mental fatigue (P = 0.0005) by the end of the experiment, though this did not affect balance. These findings highlight the sensitivity of standing balance to VR optic flow parameters and the stability of balance responses over prolonged VR exposure, even with perceived fatigue. This research advances our understanding of sensory integration in postural control and informs the use of VR for research, rehabilitation, and entertainment.

Postural stability assessment in expert versus amateur basketball players during optic flow stimulation

Angle of gaze and optic flow direction modulate body sway

Human observers can detect their heading direction on a short time scale on the basis of optic flow. We investigated the visual perception and reconstruction of visually travelled two-dimensional (2-D) trajectories from optic flow, with and without a landmark. As in our previous study, seated, stationary subjects wore a head-mounted display in which optic-flow stimuli were shown that simulated various manoeuvres: linear or curvilinear 2-D trajectories over a horizontal plane, with observer orientation either fixed in space, fixed relative to the path, or changing relative to both. Afterwards, they reproduced the perceived manoeuvre with a model vehicle, whose position and orientation were recorded. Previous results had suggested that our stimuli can induce illusory percepts when translation and yaw are unyoked. We tested that hypothesis and investigated how perception of the travelled trajectory depends on the amount of yaw and the average path-relative orientation. Using a structured visual environment instead of only dots, or making available additional extra-retinal information, can improve perception of ambiguous optic-flow stimuli. We investigated the amount of necessary structuring, specifically the effect of additional visual and/or extra-retinal information provided by a single landmark in conditions where illusory percepts occur. While yaw was perceived correctly, the travelled path was less accurately perceived, but still adequately when the simulated orientation was fixed in space or relative to the trajectory. When the amount of yaw was not equal to the rotation of the path, or in the opposite direction, subjects still perceived orientation as fixed relative to the trajectory. This caused trajectory misperception because yaw was wrongly attributed to a rotation of the path: path perception is governed by the amount of yaw in the manoeuvre. Trajectory misperception also occurs when orientation is fixed relative to a curvilinear path, but not tangential to it. A single landmark could improve perception. Our results confirm and extend previous findings that, for unambiguous perception of ego-motion from optic flow, additional information is required in many cases, which can take the form of fairly minimal, visual information.