Biomedical subjects

John F Greany

Publications and source records attributed to John F Greany.

3 recordsLinked to original sources

PubMed2003

Aging and saccade-stepping interactions in humans.

Saccade-stepping interactions were compared in older and young persons to determine if visual anchoring theory could be applied to stepping behavior in both groups. Subjects rapidly stepped onto a platform. In some trials, a translucent shield was used to prevent visual fixation. Both elderly and younger subjects initiated downward saccades prior to footlift, but saccade-step latency was significantly longer for the elderly. Regardless of age, working memory was not sufficient to guide stepping in the absence of visual fixation. The findings support visual anchoring theory by demonstrating that older and young persons generate anticipatory downward saccades which precede the stepping action. Changes in the latency of saccade-step coupling with aging were attributed to slowed processing of visual anchors for obstacle avoidance. The central nervous system appears to accommodate age-related processing delays by initiating the down saccade well in advance of platform footlift, independently from stepping velocity.

Adult↗

PubMed2003

Saccade-stepping interactions revise the motor plan for obstacle avoidance.

The authors used a stimulus-response compatibility paradigm to assess the effect of changing the estimated time to obstacle contact. A limb-selection cue was presented in different phases of gait to young (n = 5) and to older (n = 4) adults while they were moving toward a foam obstacle in the walking path. A downward saccade was initiated after the cue; the saccade typically occurred during the stance phase of the target limb (the foot cued to lead the step over the obstacle). The mean saccade-step latency after the cue was on the order of -500 ms in both young and elderly participants. On reaching the obstacle, both groups generated an upward saccade approximately -300 ms before target footlift in both groups. Saccades following the limb-selection cue appeared to direct the gaze toward footfall targets just beyond the obstacle, whereas saccades generated just before obstacle footlift moved the gaze to the forward-looking direction. The elderly had significantly longer saccade-trailing-footlift latencies and prolonged gaze-fixation times than did the younger adults. Transient disruptions in optical flow appeared to be necessary for successful obstacle-avoidance behavior when there was an unexpected change in the estimated time to obstacle contact.

Adult↗

PubMed2002

Eye-head coordination during postural perturbation as a predictor of falls in community-dwelling elderly women.

OBJECTIVES: To assess the functional significance of eye-head coordination during postural perturbations and to determine the contribution of angular vestibulo-ocular reflex (AVOR) suppression to the prediction of 1-year fall history in community-dwelling elderly women. DESIGN: Descriptive analysis of factors correlated with falls. SETTING: Community-based independent and senior assisted living facilities. PARTICIPANTS: Volunteer sample of 38 older women (mean age +/- standard deviation, 81.6+/-3.9y; range, 74-92y). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Multiple and logistic regression variables (slope coefficients, partial R2, percent-correct fall history classifications) and fall prediction equations generated by using minimal sets of predictor variables. RESULTS: Instantaneous AVOR gain and sedative use were predictors of 1-year history of falls in all minimal sets of predictor variables. R2 for the prediction models varied from.47 to.62 and indicated substantial shared variance with the 1-year history of falling. Elderly women who failed to suppress the AVOR gain were 18 times more likely to have experienced a fall in the past year compared with elderly women who showed AVOR suppression (odds ratio=18; 95% confidence interval, 1.63-198.42). CONCLUSIONS: When controlling for all other variables in the model, instantaneous AVOR gain accounted for nearly 30% of the variance of fall history. The strong association between 1-year fall history, the use of sedatives, and changes in the AVOR gain supports a functional link between AVOR suppression and effective balance in elderly women.

Accidental Falls↗