Biomedical subjects

Leonard S Mark

Publications and source records attributed to Leonard S Mark.

3 recordsLinked to original sources

PubMed2005

Information for step length adjustment in running.

The purpose of this study was to directly test the hypothesis that the tau parameter, as introduced by Lee et al. [Lee, D. N., Lishman, J. R., & Thomson, J. A. (1982). Regulation of gait in long jumping. Journal of Experimental Psychology: Human Perception and Performance, 8, 448-459] and Warren et al. [Warren, W. H., Young, D. S., & Lee, D. N. (1986). Visual control of step length during running over irregular terrain. Journal of Experimental Psychology: Human Perception and Performance, 12, 259-266], is the primary information used to regulate step length in running toward a ground target. Visual information available to research participants performing a facsimile of a long jump approach run was manipulated, and the effects on task performance and running gait were observed. Task performance and running gait were unaffected or minimally affected by (a) a perturbation of the normal optical expansion of the target, (b) elimination of global optical flow - including the focus of expansion, and (c) elimination or severe degradation of visual information about distance from the target as well as running velocity. The findings are inconsistent with notions that time-to-arrival with a ground target while running is predominantly specified optically by (a) local tau, (b) global tau, or (c) a distance/velocity computational strategy. A multisensory tau hypothesis regarding informational support for step length adjustment in running is offered.

Adaptation, Physiological↗

PubMed2004

Scaling affordances for human reach actions.

A methodology developed by Cesari and Newell [Cesari, P., & Newell, K. M. (1999). The scaling of human grip configuration. Journal of Experimental Psychology: Human Perception and Performance 25, 927-935; Cesari, P., & Newell, K. M. (2000). The body-scaling of grip configurations in children aged 6-12 years. Developmental Psychobiology 36, 301-310] was used to delineate the roles of an object's weight (W) and distance (D) as well as the actor's strength (S) in determining the macroscopic action used to reach for the object. Participants reached for objects of five different weights placed at 10 distances. The findings of a single discriminant analysis revealed that when object weight is scaled in terms of each individual's strength and reach distance is scaled in terms of each individual's maximum-seated reach distance, a single discriminant analysis was able to predict 90% of the reach modes used by both men and women. The result of the discriminant analysis was used to construct a body-scaled equation, K=lnD+ln(W/S)/36, similar in form to the one derived by Cesari and Newell, accurately predicted the reach action used. Our findings indicate that Cesari and Newell's method can identify a complex relationship between geometric and dynamic constraints that determine the affordances for different reach actions.

Adult↗

PubMedDate not supplied

Effect of a back belt on reaching postures.

OBJECTIVE: The present study investigated the effect of a back belt on reach actions. SUBJECTS: Sixteen undergraduate college students (8 male students, 8 female students) ranging in age from 18 to 22 years. Thirteen subjects were included in the final analysis. SETTING: The Department of Psychology at Miami University, Oxford, Ohio METHODS: Using a well-established set of procedures developed in our laboratory for studying reaching, seated adult participants reached for and retrieved an object placed at various distances from them. Reach distances included values both closer than and farther than each subject's maximum seated reach. The reach task had 2 conditions: picking up and retrieving a small block and skewering and retrieving a small bead with a needle. For each task condition, each subject either wore the belt or did not use a belt. RESULTS: Results indicate that when subjects wore the belt while reaching, they tended to have initial transition points (sitting to nonsitting) closer to their bodies than while not wearing the belt. That is, for a distant object, subjects were more likely to raise their bodies out of the chair rather than perform an extreme seated reach, possibly acting to preserve a greater margin of safety. CONCLUSIONS: The back belt consistently modified reaching postures by limiting extreme ranges of motion during a task that required enhanced stability. Furthermore, the methodology and analysis presented in this article when applied to chiropractic will allow us to begin thoughtful investigation of the effects of chiropractic adjustments on postural transitions and margin of safety.

Adult↗