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Vestibular motion perception declines with age, increasing the risk of falling substantially. We performed a two-week perceptual learning intervention using a self-motion direction discrimination task (2800 training trials per person) on a 6 degrees of freedom motion platform in healthy older adults (n = 40, aged 70-88 yr). Linear inter-aural and angular roll tilt vestibular thresholds improved with training (95% credible interval for pre/post difference), suggesting altered sensitivity post-training. Moreover, improved perceptual abilities transfer to actual posture (reduced sway) and gait parameters. Passive self-motion discrimination training provides a new and promising way to counteract age-related sensory decline. It can reduce the risk of falling, and thereby maintain individual autonomy and quality of life.

Major depressive disorder (MDD) is characterized by psychomotor retardation whose underlying neural source remains unclear. Psychomotor retardation may either be related to a motor source like the motor cortex or, alternatively, to a psychomotor source with neural changes outside motor regions, like input regions such as visual cortex. These two alternative hypotheses in main (n = 41) and replication (n = 18) MDD samples using 7 Tesla MRI are investigated. Analyzing both global and local connectivity in primary motor cortex (BA4), motor network and middle temporal visual cortex complex (MT+), the main findings in MDD are: 1) Reduced local and global synchronization and increased local-to-global output in motor regions, which do not correlate with psychomotor retardation, though. 2) Reduced local-to-local BA4 - MT+ functional connectivity (FC) which correlates with psychomotor retardation. 3) Reduced global synchronization and increased local-to-global output in MT+ which relate to psychomotor retardation. 4) Reduced variability in the psychophysical measures of MT+ based motion perception which relates to psychomotor retardation. Together, it is shown that visual cortex MT+ and its relation to motor cortex play a key role in mediating psychomotor retardation. This supports psychomotor over motor hypothesis about the neural source of psychomotor retardation in MDD.

In this paper, we show that the model we proposed earlier to account for the disparity vergence eye movements (disparity vergence responses, or DVRs) in response to horizontal and vertical disparity steps of white noise visual stimuli also provides an excellent description of the short-latency ocular following responses (OFRs) to broadband stimuli in the visual motion domain. In addition, we reanalyzed the data and applied the model to several earlier studies that used sine-wave gratings (single or a combination of two or three gratings) and white noise stimuli. The model provides a very good account of all of these data. The model postulates that the short-latency eye movements-OFRs and DVRs-can be accounted for by the operation of two factors: an excitatory drive, determined by a weighted sum of contributions of stimulus Fourier components, scaled by a global contrast normalization mechanism. The output of the operation of these two factors is then nonlinearly scaled by the total contrast of the stimulus. Despite different roles of disparity (horizontal and vertical) and motion signals in visual scene analyses, the earliest processing stages of these different signals appear to be very similar.

Recently, there has been a resurgence in experimental and conceptual efforts to understand how brain rhythms can serve to organize visual information. Oscillations can provide temporal structure for neuronal processing and form a basis for integrating information across brain areas. Here, we use a bistable paradigm and a data-driven approach to test the hypothesis that oscillatory modulations associate with the integration or segregation of visual elements. Spectral signatures of perception of bound and unbound configurations of visual moving stimuli were studied using magnetoencephalography (MEG) in ambiguous and unambiguous conditions. Using a 2 × 2 design, we were able to isolate correlates from visual integration, either perceptual or stimulus-driven, from attentional and ambiguity-related activity. Two frequency bands were found to be modulated by visual integration: an alpha/beta frequency and a higher frequency gamma-band. Alpha/beta power was increased in several early visual cortical and dorsal visual areas during visual integration, while gamma-band power was surprisingly increased in the extrastriate visual cortex during segregation. This points to an integrative role for alpha/beta activity, likely from top-down signals maintaining a single visual representation. On the other hand, when more representations have to be processed in parallel gamma-band activity is increased, which is at odds with the notion that gamma oscillations are related to perceptual coherence. These modulations were confirmed in intracranial EEG recordings and partially originate from distinct brain areas. Our MEG and stereo-EEG data confirms predictions of binding mechanisms depending on low-frequency activity for long-range integration and for organizing visual processing while refuting a straightforward correlation between gamma-activity and perceptual binding. PRACTITIONER POINTS: Distinct neurophysiological signals underlie competing bistable percepts. Increased alpha/beta activity correlate with visual integration while gamma correlates with segmentation. Ambiguous percepts drive alpha/beta activity in the posterior cingulate cortex.

Attention and crossmodal interactions are closely linked through a complex interplay at different stages of sensory processing. Within the context of motion perception, previous research revealed that attentional demands alter audiovisual interactions in the temporal domain. In the present study, we aimed to understand the neurophysiological correlates of these attentional modulations. We utilized an audiovisual motion paradigm that elicits auditory time interval effects on perceived visual speed. The audiovisual interactions in the temporal domain were quantified by changes in perceived visual speed across different auditory time intervals. We manipulated attentional demands in the visual field by having a secondary task on a stationary object (i.e., single- vs. dual-task conditions). When the attentional demands were high (i.e., dual-task condition), there was a significant decrease in the effects of auditory time interval on perceived visual speed, suggesting a reduction in audiovisual interactions. Moreover, we found significant differences in both early and late neural activities elicited by visual stimuli across task conditions (single vs. dual), reflecting an overall increase in attentional demands in the visual field. Consistent with the changes in perceived visual speed, the audiovisual interactions in neural signals declined in the late positive component range. Compared with the findings from previous studies using different paradigms, our findings support the view that attentional modulations of crossmodal interactions are not unitary and depend on task-specific components. They also have important implications for motion processing and speed estimation in daily life situations where sensory relevance and attentional demands constantly change.

Recent work suggests that our brains may generate subtle, false motion signals streaming from other people to the objects of their attention, aiding social cognition. For instance, brief exposure to static images depicting other people gazing at objects made subjects slower at detecting subsequent motion in the direction of gaze, suggesting that looking at someone else\'s gaze caused a directional motion adaptation. Here we confirm, using a more stringent method, that viewing static images of another person gazing in a particular direction, at an object, produced motion aftereffects in the opposite direction. The aftereffect was manifested as a change in perceptual decision threshold for detecting left vs. right motion. The effect disappeared when the person was looking away from the object. These findings suggest that the attentive gaze of others is encoded as an implied agent-to-object motion that is sufficiently robust to cause genuine motion aftereffects, though subtle enough to remain subthreshold.

BACKGROUND: To better personalize treatment and monitor recovery of individuals with low back pain, objective tests of sensorimotor functions, such as lumbar proprioception, must be selected based on their reliability and validity. The primary objective of this study was to test the concurrent validity of three measures of lumbar proprioception.
METHODS: Thirty-one participants performed three lumbar proprioception tests (motion perception threshold, active and passive joint positioning sense), a whole-body mobility and balance (time up-and-go) and two trunk-specific postural control (threshold of stability and sensor-based sway measures) tests.
RESULTS: Only the motion perception threshold proprioception test showed some validity, correlating with the trunk-specific postural control tests [r range (positive values): 0.37 to 0.60]. The three lumbar proprioception measures were not correlated to each other. The threshold of stability measure was correlated with the time up-and-go (r = 0.37) and trunk-specific (sensor-based sway measures) postural control [r range (positive values): 0.48 to 0.77] tests.
CONCLUSIONS: The present study generated three original findings. Only the motion perception threshold proprioception test demonstrated its concurrent validity. In fact, the three lumbar proprioception tests performed in the present study were not correlated to each other, thus assessing different constructs. Finally, the threshold of stability protocol was validated against other tests. These findings will help in selecting the most appropriate lumbar proprioception measures to study the effects of exercise treatments in patients with back pain.

For successful interactions with the world, we often have to evaluate our own performance. Although eye movements are one of the most frequent actions we perform, we are typically unaware of them. Here, we investigated whether there is any evidence for metacognitive sensitivity for the accuracy of eye movements. Participants tracked a dot cloud as it followed an unpredictable sinusoidal trajectory and then reported if they thought their performance was better or worse than their average tracking performance. Our results show above-chance identification of better tracking behavior across all trials and also for repeated attempts of the same target trajectories. Sensitivity in discriminating performance between better and worse trials was stable across sessions, but judgements within a trial relied more on performance in the final seconds. This behavior matched previous reports when judging the quality of hand movements, although overall metacognitive sensitivity for eye movements was significantly lower.

Motion can produce large changes in the apparent locations of briefly flashed tests presented on or near the motion. These motion-induced position shifts may have a variety of sources. They may be due to a frame effect where the moving pattern provides a frame of reference for the locations of events within it. The motion of the background may act through high-level mechanisms that track its explicit contours or the motion may act on position through the signals from low-level motion detectors. Here we isolate the contribution of low-level motion by eliminating explicit contours and trackable features. In this case, motion still supports a robust shift in probe locations with the shift being in the direction of the motion that follows the probe. Although robust, the magnitude of the shift in our first experiment is about 20% of the shift seen in a previous study with explicit frames and, in the second, about 45% of that found with explicit frames. Clearly, low-level motion alone can produce position shifts although the magnitude is much reduced compared to that seen when high-level mechanisms can contribute.