Resolving an ambiguous perspective figure depends on internal references built from visual, vestibular, and proprioceptive cues and, for depicted objects, on their relation to the observer’s body. Discrete head orientations between up-right and inverted have rarely been compared on the same perspective stimulus. This study tested whether the orientation of the head modulates the rate of perceptual reversals and the identity of the first percept while the stimulus on the screen remained fixed. Sixty-four adults (Mage = 21.45, SD = 2.30; 34 women) viewed the Schröder staircase on a stationary monitor for 12 s in four head orientations—up-right, 45° left, 45° right, and up-side-down—in one of two alternating orders; the figure’s 180° symmetry made the up-right and inverted retinal images nominally identical. Reversal rate decreased with head tilt: up-right (M = 5.59) > 45° left (M = 4.08) > 45° right (M = 3.39) ≥ up-side-down (M = 3.05); F(3, 189) = 61.15, p < .001, η2p = .49; the 45° right and up-side-down conditions did not differ reliably. The first percept also reorganized: the normal staircase emerged first in 100
This exploratory study investigates the influence of an inactive lifestyle on anticipatory locomotor adjustments (ALA) in older adults during pedestrian circumvention tasks. We hypothesized that older adults with an inactive lifestyle would exhibit more cautious ALA compared to their physically active counterparts. The study included 28 participants, divided into two groups: 14 healthy, physically active older adults (OAA) and 14 healthy, physically inactive older adults (OIA). Participants navigated a virtual environment while kinematic, electromyographic, and visual data were recorded. Results indicated that during both circumvention and unobstructed walking tasks, OIA walked significantly slower and had higher levels of muscle co-contraction around the ankle joints as compared to OAA, suggesting a compensatory mechanism aimed at enhancing joint stability. No significant differences were found between groups in terms of distance from the pedestrian at deviation onset, minimum clearance, or gaze behavior. However, OIA showed greater between-participant variability in the distance at deviation onset. Exploratory post-hoc analyses suggested a potential influence of sex within the OIA group. Overall, this exploratory study demonstrated that physical activity level influences general locomotor performance, but not key ALA variables during circumvention, except for variability in distance at deviation onset. Sex-specific factors should be considered in future research.
Step initiation requires the coordinated preparation of posture and movement, yet how first step constraints influence multi-muscle synergies stabilizing the center of pressure (COP), anticipatory synergy adjustments (ASAs), and early postural adjustments (EPAs) remains poorly understood. This study examined the effects of stepping surface height and step length on these outcomes in healthy young adults. Sixteen participants initiated a step under five conditions: level, step-up, step-down, short-step, and long-step. Surface electromyography was recorded from 16 leg and trunk muscles bilaterally, and COP coordinates were obtained from a force platform. The uncontrolled manifold approach was used to quantify multi-muscle synergies and ASAs stabilizing COP in the anteroposterior (AP) and mediolateral (ML) directions during steady-steady and around the foot lift-off −25:+25 ms. Multi-muscle synergies stabilizing COP-AP were present across all conditions, and their index did not differ significantly across stepping conditions, supporting the view that steady-state synergic organization reflects the demands of upright stance rather than anticipation of the upcoming step. Synergies stabilizing COP-ML were absent in all conditions. ASAs were not detected in any condition or direction, suggesting that step initiation relies more on EPA-based rather than synergy-level anticipatory mechanisms. Stepping surface height significantly influenced EPA onset timing and COP displacement magnitude in both directions, with the step-down condition producing earlier EPA onset and smaller displacements than the step-up condition. Step length did not significantly affect EPAs. These findings reveal a dissociation between synergic muscle organization and COP trajectory control and highlight the asymmetric postural demands of descending versus ascending steps during step initiation.
Sport-related concussions (SRC) commonly affect vision and cognition, but there is limited understanding of how concurrent balance and exertion demands may affect visual-cognitive performance beyond symptom resolution. Purpose To determine if a dynamic visual acuity (DVA) task performed during standing and walking could differentiate performance between athletes with and without concussion history. Methods Interuniversity athletes (N = 30, age = 20.9 years ± 1.4) with SRC history who were asymptomatic (SRC = 14; females = 6) were compared to athletes without SRC (CONTROL = 16; female = 7). A DVA task was completed while seated, standing, and during low- and moderate-intensity treadmill walking. A Tumbling ‘E’ target was presented randomly in either random walk (R) or horizontal (H) motion (2.31 m/s), in one of four orientations; responses were selected using a handheld keypad. Performance was characterized as a change in DVA score from Seated (logMAR) and response time (RT, ms). A linear mixed-effects model was fitted for DVA change scores and a generalized mixed effects model for median RT. Results The SRC group exhibited worse DVA change scores during standing and walking compared to CONTROL (p < .05) during R-motion only. Whereas both groups responded faster during treadmill walking for both R- and H-motion (p < .001). Only two athletes (14
Deep brain stimulation (DBS) is an alternative to ablative functional neurosurgeries. The basolateral amygdala (BLA) is a potential DBS target for treating psychiatric disorders. However, understanding the associated behavioral and cognitive effects is necessary for safety and tolerability concerns. Therefore, we investigated potential acute effects of unilateral BLA DBS. Adult male Wistar rats were implanted with monopolar electrodes in the right BLA. In Experiment 1, different groups of animals were stimulated for 10 min with either high-frequency (HFS, 130 Hz) or low-frequency (LFS, 20 Hz) stimulation using different stimulation intensities (0 [Control], 10, 50, or 100 µA). Immediately after stimulation, animals were tested in the elevated plus-maze (EPM) and subsequently in the open field test (OFT). In Experiment 2, two groups of animals were subjected to a fear-conditioning protocol and stimulated with HFS or LFS (50 µA) immediately after conditioning. Animals were then tested for short- (2 h) and long-term (24 h) fear memory consolidation. BLA DBS showed no significant effects on: (i) anxiety-like behavior expression for HFS (p = 0.46) or LFS (p = 0.37); (ii) locomotor activity (HFS, p = 0.12; LFS, p = 0.60), in terms of distance traveled in the OFT, or (iii) fear memory consolidation (HFS, p = 0.31; LFS, p = 0.68). Under the stimulation parameters and experimental conditions tested, acute unilateral BLA DBS did not significantly affect spontaneous locomotor activity, anxiety-like behavior, or fear memory consolidation in rats. These results provide information relevant to the tolerability and safety of amygdala DBS.
