Visual and motor processes involved in the control of collisions
Colliding with objects in our environment is a common feature of daily activity. Skilled behaviour often involves the precise regulation of these collisions. Traditional approaches to skilled behaviour are criticised for confusing the constraints of their approach with behavioural constraints. The following investigation combines aspects of several approaches laid out in the Introductory Chapter 1 to examine the visual and motor processes involved in controlling collisions. In Chapter 2 performance is assessed in a one-handed catching task, when the physical characteristics of the ball are manipulated. The results indicate that viewing-time and the nature of grasping affect perfomance. In Chapters 3 and 4 a hitting task is used to investigate the visual processes involved in intercepting an object. Task performance is compared across monocular and binocular viewing conditions. In Chapter 3, results show that timing performance is unaffected by this manipulation and this provides support for the direct pick up of time-to-collision information. In Chapter 4, binocular information is found to be necessary for the spatial location of an object. In Chapters 5, 6 and 7, a tapping task is used to investigate the motor aspects involved in controlling a collision. In Chapter 5 force waveforms recored when tapping on a strain gauge vary in accordance with 'external' and 'internal' manipulations of load and stiffness. In Chapter 6, a mass-spring model is proposed to describe the collision. Changes in impact are related to changes in the parameters of the model. These effects are simulated on a computer. In Chapter 7, the mechanisms of effecting collision change are directly investigated from kinematic recordings. The results suggest that speed of impact is the controlled parameter. The findings are compatible with the mass-spring model. The final Chapter concludes that a multi-dimensional approach is required for a full understanding of skilled-motor behaviour. The possible applications of this approach to the assessment of clumsiness are discussed.