CONCEPTS OF DISABILITY - THE ACTIVITY SPACE MODEL

This paper describes a new conceptual framework for functional assessm ent, the Activity Space Model(ASM). According to this model, functiona l impairments may lead to restrictions in an individual's activity spa ce, a multidimensional space that represents human potential for activ ity. For each elementary ability, restrictions in the corresponding di mension of the activity space can be evaluated by deriving a difficult y curve that depicts the relationship between the level of performance and the psychophysical cost of activity. The effect of disease on dai ly functioning is explained in terms of a tradeoff between the psychop hysical cost and the value of each act of behavior to the disabled ind ividual. These two constructs are measured on the same scale and expre ssed in units of difficulty. The location of each task within the acti vity space in relation to the difficulty curve determines whether it w ill be performed or avoided at a given point in time. The ASM has both theoretical and practical implications. It offers a new, integrated p erspective on disability and suggests new strategies for developing an d evaluating functional assessment measures.