Visuomotor control of locomotion and the effects of aging and stroke
Why this work is in the frame
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Bibliographic record
Abstract
Vision is arguably the most important sensory cue for the control of goal-directed locomotion. Optic flow, broadly defined as the pattern of light at the eye of a person moving through the environment, provides strong cues on the direction of locomotion, also known as heading. To date, most studies have only investigated the use of optic flow for heading in healthy young subjects. However, the capacity for visual processing can decline with advancing age or a neurological insult, such as stroke. These changes could impact on the control of heading and locomotion. The purpose of this thesis was to explore the role of optic flow in the control of locomotion in older adults and in stroke patients. In the first study, 2 groups of subjects (young: n=9, age 21.56 ± 3.20; old: n=9, age 66.11 ± 3.95) were instructed to walk straight in a virtual environment. As they progressed forward, the location from which the scene was expanding from, also know as the focus of expansion (FOE), was offset with a translation of 20° or 40° either to the left or right of the midline of the virtual scene. Young adults responded by displacing their centre of mass (CoM) mediolaterally in the direction opposite to the FOE shift, thus correcting their virtual trajectory so that they perceived walking straight in the virtual environment. In contrast, older adults showed very little trajectory corrections to the optic flow, resulting in large heading errors. In the second study, 10 young (age 23.49 ± 4.72) and 10 older adults (age 76.22 ± 3.11) were instructed to walk straight in a virtual environment where the FOE was gradually rotated until reaching 40° to the right or left at the end of the walking trial. Young adults displayed very small net heading errors in the virtual environment and responded by physically reorienting their heading and head in the direction opposite to the FOE rotation. Older adults showed similar responses, though they had smaller head rotations and slightly larger errors. Taken together, these 2 studies indicate that the effects of aging on the control of heading from optic flow are dependent on the type of flow presented and that the utilization of rotational flows while walking are less susceptible to aging than translational flows. In the third study, the same groups of healthy young and older adults (n=10 each) were tested on their ability to re-weight sensory information and maintain a straight heading in the physical environment while being exposed to rotational flows, as they walked at normal and fast walking speeds. Older participants made significantly larger heading errors than younger adults at normal walking speeds. Fast walking speed was found to improve the heading performance of young subjects but led to even larger heading errors in the older adults. This study suggests an increased reliance on visual cues for locomotor control in older adults who are less adept in visual reweighting. In the final study, a single-subject design was used to investigate the effects of stroke on the ability to use rotational optic flow cues while walking. Nine stroke patients were instructed to walk straight in a virtual environment with the FOE rotating 40° either towards the ipsilesional or contra-lesional side. Patterns of heading responses varied, with individuals having a history of neglect consistently showing heading larger errors than those without. The presence of persistent visuomotor deficits, particularly in far space, in stroke patients with a history of visuospatial neglect, is a novel finding of this thesis. In conclusion, central nervous system changes due to aging and stroke can impact the ability to use optic flow for the control of goal-directed locomotion. The underlying changes may pertain to the processing and/or integration of visual motion information.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it