Directional acuity of whole-body perturbations during standing balance

Abstract

The ability to perceive the direction of whole-body motion during standing may be critical to maintaining balance and preventing a fall. Our first goal was to quantify kinesthetic perception of whole-body motion by estimating directional acuity thresholds of support-surface perturbations during standing. The directional acuity threshold to lateral deviations in backward support-surface motion healthy, young adults was quantified as 9.5 ± 2.4° using the psychometric method (n = 25 subjects). However, inherent limitations in the psychometric method, such as a large number of required trials and the predetermined stimulus set, may preclude wider use of this method in clinical populations. Our second goal was to validate an adaptive algorithm known as parameter estimation by sequential testing (PEST) as an alternative threshold estimation technique to minimize the required trial count without predetermined knowledge of the relevant stimulus space. The directional acuity threshold was estimated at 11.7° ± 3.8° from the PEST method (n = 11 of 25 subjects, psychometric threshold = 10.1 ± 3.1°) using only one-third the number of trials compared to the psychometric method. Furthermore, PEST estimates of the direction acuity threshold were highly correlated with the psychometric estimates across subjects (r = 0.93) suggesting that both methods provide comparable estimates of the perceptual threshold. Computational modeling of both techniques revealed similar variance in the estimated thresholds across simulations of about 1°. Our results suggest that the PEST algorithm can be used to more quickly quantify whole-body directional acuity during standing in individuals with balance impairments.

Evaluating Sensory Acuity as a Marker of Balance Dysfunction After a Traumatic Brain Injury: A Psychophysical Approach

“…Our novel PPT outcome therefore not only reflects the perceptual and attentional indicators of balance deficit but also presents a potentially quantifiable link between the sensory acuity and functional tasks. The absence of significant correlations between the PPT and functional measures for the HC group could potentially imply less reliance on attentional mechanisms and more on their unaffected APRs (Puntkattalee et al, 2016) as well as intact attentional mechanisms.…”

Perception of whole-body motion during balance perturbations is impaired in Parkinson’s disease and is associated with balance impairment

“…The first perturbation of each pair was delivered in the backward direction, causing the body center of mass to be displaced anteriorly with respect to the ankles. The second perturbation of each pair was delivered 0.5 s after the first perturbation ended, and deviated in a pseudo-random fashion either to the left or to the right from the backward direction, and by an amount ∆ determined adaptively online using the PEST with identical parameters as Puntkattalee et al [28], with an initial ∆ of +3° or -3°, an initial step size of 4°, and a stopping step size criterion of 0.5°.…”

“…Verbal responses from patients with hypophonia were repeated by a nearby study staff member for recording as necessary. During testing, participants held a small push-button device to enable comparisons with earlier results [28]; signals from the handheld device were not examined.…”

“…Additional analyses were performed, including analyses of: 1) Differences in threshold values between PD/NOA participants and existing data of young healthy adults [28], 2) Clinical and demographic features associated with failure to complete testing protocol, and, 3) Clinical and demographic features associated with incomplete threshold convergence during the testing protocol, 4) Associations between MDS-UPDRS-III motor symptom asymmetry [39] and threshold values, and, 5) Whether direction threshold magnitude influenced the likelihood of convergence (Supplementary Materials S1).…”

“…We previously developed a balance testing paradigm to quantify the perception of whole-body motion direction during backward perturbations to standing balance in young healthy subjects using a "Parameter Estimation by Sequential Testing" (PEST) algorithm [27,28]. We quantified just-noticeable differences to lateral deviations during backward support-surface translations while standing using a two-alternative forced choice paradigm, and identified a directional threshold of about 10° [28]. We demonstrated that the PEST algorithm required far fewer trials than conventional psychophysical methods, making the testing paradigm feasible in clinical populations like PD.…”