The purposes of this study were: (1) to describe developmental differences in performance and cognitive strategies during a perceptual-motor task, and (2) to examine the relationships between cognitive strategies and performance. Sixty healthy children, ages 7, 9, and 11, were required to tap reciprocally with a pen between two targets. Cognitive strategies were measured by: pen marks on the paper, pen arc, and trunk movements. Cognitive strategy profiles were reported based on grade and performance level. These profiles help us to understand how children approach the task and guide the motor action. Clinical applications of the findings are described in terms of speed-accuracy tradeoff, shift and discontinuous to continuous approach to the task, use of affordances, and free(z)ing of degrees of freedom.
The time derivative (tau) of the inverse of the relative rate of optical expansion (tau) may have critical values with potential implications for controlling activity. The present research addresses the particular hypothesis that tau < -0.5 specifies "unsafe" collision courses and tau > or = -0.5 specifies "safe" collision courses. Optical expansion patterns were simulated on a computer with -1.0 < or = tau < 0 and judged as suggesting a "hard" or "soft" collision. tau < -0.5 led to significantly different decisions from tau > or = -0.5, but the critical value of -0.5 was not perceived reliably as soft, a deviation possibly due to discretely approximating continuous functions. Additional experiments evaluated terminal rates of change and display duration and examined the effects of biasing the presented displays toward the soft or the hard end of the tau continuum. The results were consistent with the tau hypothesis.
Abstract
This experiment extended Warren's 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. Subjects 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.
Mean age of young men was 23.5, of old 71.3 years.
| Group | Warren's predictiona Mean (SD) | Actual Mean (SD) | Perceived Mean (SD) |
|---|---|---|---|
| Young tall | .93 (.02) | .96 (.07) | .88 (.11) |
| Young short | .92 (.04) | 1.00 (.19) | .95 (.17) |
| Old tall | .89 (.04) | .73 (.07) | .75 (.09) |
| Old short | .91 (.04) | .62 (.15) | .62 (.15) |
RHmax= LEGL + UPLL - LOWLL
The occupation of play, as mutually engaged in by parents and young children, is theorized to be central to the development of social competence. Two conceptual heuristics, Vygotsky's zone of proximal development, and Gibson's affordances, frame this examination of play's role in the child's ability to generate adaptive responses and capitalize on environmental opportunities fostering social competence. Research describing mother-child interaction during play is used to illustrate the mother's orchestration and grading of social interactions to stretch the child's emerging abilities and optimize the child's performance. Finally, the practical application of these concepts and specific strategies which occupational therapists can use to "tune" their assistance to the needs of young children and to foster their development are described.
Abstract
Previous work has shown that both the perceived and actual critical (maximum) heights of surfaces that afford "sitting on " and "climbing on" can be expressed as constant proportions of each actor's leg length. The current study provides evidence that these judgments of critical action boundaries are based on an existing source of size and distance information that is already scaled with reference to the actor's eyeheight.
In Experiment 1 changes in judgments of "perceived eyeheight" (an index of the intrinsic scalar) as a function of viewing distance were shown to be highly correlated with changes in the maximum height that was perceived to afford sitting on or climbing on.
In Experiments 2 and 3 observers wore 10-cm blocks and made judgments about whether the heights of various surfaces afforded sitting or climbing. The use of eyeheight-scaled information as the basis for their estimates predicted the obtained pattern of errors in these judgments. With a modicum of experience wearing the blocks, however, observers were able to retune accurately their critical action boundary to a degree that would not have been predicted from their consistent overestimation of the height of the block on which they were standing. These results have implications for understanding how observers obtain information about their specific action boundary.
Abstract
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.
In choice reaction time, stimuli and responses in some combinations (e.g., based on spatial arrangement) are faster than in other combinations. To test whether motion toward a position yields faster responses at that position, a computer-generated square in front of one hand appeared to move either toward that hand or toward the other hand. Compatible responses (e.g., motion toward left hand/left response) were faster than incompatible responses, even when that opposed traditional positional compatibility. In Experiment 2, subjects responded to the same stimuli but with both hands left, right, or on the body midline. Medial responses were the fastest, showing that destination, rather than mere relative position, was a critical variable. It was suggested that spatial compatibility effects are not unique to position but apply to a variety of task situations, describable by J.J. Gibson's theory of affordances, in which he claims that one perceives the actions (e.g., catching) permitted in a situation.
Abstract
Advancing or retreating so as to maintain a projectile's constant vertical optical velocity was suggested by Chapman (1968) as a possible basis for locomotion in ball catching. Three experiments examined this thesis. In Experiments 1 and 2, the positions of balls and catchers were videotaped to see if the movements of the catchers canceled optical acceleration. Such canceling was indeed observed until just prior to the catch for hand-thrown balls (Experiment 1). The monocular availability of the information predicts success with monocular viewing, confirmed in Experiment 2 with machine-thrown balls. In Experiment 3, observers judged whether a ball (represented as a moving dot on a computer screen) would land at, in front of, or behind them. Performance was above chance, but only some observers used acceleration. Together, the experiments provide broad, though not unequivocal, support for the utilization of optical acceleration to guide locomotion in catching.
Abstract
The catchableness of a fly ball depends on whether the catcher can get to the ball in time; accurate judgments of catchableness must reflect both spatial and temporal aspects. Two experiments examined the perception of catchableness under conditions of restricted information pickup. Experiment 1 compared perceptual judgments with actual catching and revealed that stationary observers are poor perceivers of catchableness, as would be expected by the lack of information about running capabilities. In Experiment 2, participants saw the 1st part of balltrajectories before their vision was occluded. In 1 condition, they started to run (as if to catch the ball) before occlusion; in another, they remained stationary. Moving judgments were better than stationary judgments. This supports the idea that perceiving affordances that depend on kinematic, rather than merely geometric, body characteristics may require the relevant action to be performed.
Abstract
Perceiving the affordance of a tool requires the integration of several complementary relationships among actor, tool, and target. Highers order affordance structures are introduced to deal with these forms of complex action from an ecological-realist point of view. The complexity of the higher order affordance structure was used to predict the difficulty of perceiving the tool function. Predictions were tested in 3 experiments involving children between 9 months and 4 years old. In a classical tool use task dating back to W. Kohler, a desirable target was obtained by using a hook as a tool. The relative positions of the hook and the target were systematically varied to obtain structures differing in complexity. The observed difficulty of the task was found essentially in accordance with the theoretical complexity of the higher order affordance structures involved in perceiving the tool function.
Abstract
How do animals visually guide their activities in a cluttered environment? Gibson (1979) proposed that they perceive what environmental objects offer or afford for action. An analysis of affordances in terms of the dynamics of an animal-environment system is presented. Critical points, corresponding to phase transitions in behavior, and optimal points, corresponding to stable, preferred regions of minimum energy expenditure, emerge from variation in the animal-environment fit. It is hypothesized that these points are constants across physically similar systems and that they provide a natural basis for perceptual categories and preferences. In three experiments these hypotheses are examined for the activity of human stair climbing, by varying riser height with respect to leg length. The perceptual category boundary between "climbable" and "unclimbable" stairs is predicted by a biomechanical model, and visually preferred riser height is predicted from measurements of minimum energy expenditure during climbing. It is concluded that perception for the control of action reflects the underlying dynamics of the animal-environment system.
Abstract
OBJECTIVE: This study investigated whether affording objects with different levels of functional support would have an impact on reaching performance in patients after cerebrovascular accident (CVA) and in adults who were neurologically intact. Reaching performance was quantitatively analyzed, using several kinematic variables. METHOD: Two groups, 14 participants after CVA and 24 age-matched adults who were neurologically intact, performed a food chopping task under two conditions: enriched affordances and impoverished affordances. Enriched affordances involved reaching forward to a chopper and pushing down on the handle to chop a fresh mushroom. Impoverished affordances involved reaching forward to a simulated chopper (i.e., a chopper covered with cardboard) without anything in it and then pushing the handle down. Reaching movement was measured by a three-dimensional motion analysis system. RESULTS: For the CVA group, the enriched condition of reaching to chop the mushroom resulted in more efficient, direct, smooth, and preplanned movement than the impoverished condition of reaching to push on the chopper handle. The neurologically intact group responded similarly except that the participants' movement was equally smooth, as measured by movement unit, between the two testing conditions. Force generation, as characterized by peak velocity, was similar for both conditions for both groups. CONCLUSION: The finding that enriched affordances had a positive effect on movement kinematics in both CVA and neurologically intact groups suggests that providing natural objects for completing a task and providing functional information on the objects may enhance the functional performance of persons who have had a CVA. These findings should be replicated and extended to confirm the validity of these effects and allow for generalization.