Harry J. Meeuwsen

Changing affordances in stair climbing: the perception of maximum climbability in young and older adults

This experiment extended Warrens leg-length model by investigating the relevance of leg strength and joint flexibility on perceptual judgments of climbability. From a set of 8 stairs (riser heights: 38-91 cm), 24 older and 24 young adults were asked to identify the highest stair they could climb without using their hands or knees. Ss then attempted to climb the selected stair. Tall and short young observers perceived similar action boundaries despite leg-length differences. Tall and short older adults had divergent action boundaries when a single-scale leg-length model was applied. A regression model that used flexibility and leg-strength measurements provided a better fit of the older adult data, indicating that models applying functional (kinematic and kinetic) criteria might be useful in describing lawful relationships between organisms and the environment.

Investigation of the Contextual Interference Effect in the Manipulation of the Motor Parameter of Over-All Force:

This investigation examined the contextual interference effect when manipulating over-all force in a golf-putting task. Undergraduate women (N = 30) were randomly assigned to a Random, Blocked-Random, or Blocked practice condition and practiced golf putting from distances of 2.43 m, 3.95 m, and 5.47 m during acquisition. Subjects in the Random condition practiced trials in a quasirandom sequence and those in the Blocked-Random condition practiced trials initially in a blocked sequence with the remainder of the trials practiced in a quasirandom sequence. In the Blocked condition subjects practiced trials in a blocked sequence. A 24-hr. transfer test consisted of 30 trials with 10 trials each from 1.67 m, 3.19 m, and 6.23 m. Transfer scores supported the Magill and Hall (1990) hypothesis that, when task variations involve learning parameters of a generalized motor program, the benefit of random practice over blocked practice would not be found.

Variables affecting perceptual boundaries in bipedal stair climbing

The present study examined the effects of hip joint mobility and relative leg strength on perceived and attained action boundaries in bipedal stair climbing. If action boundaries are directly perceived and action is intimately linked to perception, one should be able to quantify these boundaries (Warren, 1984) and identify what variables affect these perceived boundaries. In the present experiment the perceived and attained absolute and relative (riser height divided by leg length) action boundaries were significantly affected by hip joint flexibility. Relative leg strength also affected absolute and relative perceived action boundaries. These results clearly show that factors in addition to body size and body proportions may affect the perception of affordances and their boundaries.

ON THE PSYCHOPHYSICS OF ARM-POSITIONING MOVEMENTS

The basis for the relationship between physical stimulus and magnitude of psychological response in angular movements of the upper limbs was investigated. Participants compared movements to a standard location with movements to comparison locations and movements of a standard distance with movements of comparison distances. The results add to the controversy surrounding the explanations for the differences in psychological response magnitude of movements to locations and movements across distances. Data obtained from movements to locations and movements across distances indicated similar Weber ratios but different patterns for the just noticeable differences. The data of this and previous research suggest that the application of a prothetic continuum to arm movements is inappropriate. An alternative explanation of the differences in the perception of movements to locations and movements across distances is offered.

Psychophysics of arm movements and human aging.

The purpose of this study was to investigate possible age-related differences in the physical stimulus-psychological response relationship. Young and older adult subjects moved their arm to three standard locations or extents (25 cm, 50 cm, and 75 cm) on a linear positioning device. Seven standard comparison combinations were presented 20 times each. Subjects were asked to determine whether the comparison was different from the standard. Just noticeable difference, constant error, absolute constant error, and Weber ratios were calculated. In contrast to previous studies, the results clearly indicate that the physical stimulus-psychological response magnitude relationship for location and extent movements is best described by a metathetic continuum. We offer an explanation to account for the differences between location and extent movements for the just noticeable difference and Weber ratio. The failure to find differences between the age groups suggests that age-related declines cannot be generalized to all perceptual systems.