A perception-action framework for physical therapy for persons with neurologic dysfunction: use of therapeutic affordance and unitless ratio.
BACKGROUND AND PURPOSE: Our goal through this case study is to introduce the reader to the perception-action framework (PAF) for human action and the application of this framework to examination and treatment in physical therapy. We define the concepts of affordance, constraints, and emergent action as example concepts in the PAF and then apply these concepts to examination and treatment in physical therapy through the use of unitless ratios. At critical values of these ratios, the coordination pattern used or the action taken undergoes a shift. We offer examples that contrast some of the unique aspects of the PAF to approaches such as the hierarchical or motor program approaches that primarily focus on the nervous system influence on the motor aspects of human action. CASE DESCRIPTION: This principled approach to examination and treatment can be used with patients of all ages. Here, we provide the case of a 59-year-old, right handed male status post acute, embolic stroke with right posterior cerebral artery (PCA) and right middle cerebral artery (MCA) territory infarcts. The PAF and the specific use of unitless ratios for examination and treatment of reaching and grasping are detailed. OUTCOMES: Research supports that the unitless ratio created from the size of a cube to the range of motion of the index finger-thumb aperture defines the boundaries for the shift between a 1 handed and a 2 handed reach regardless of age. These boundary conditions are used to examine the subjects grasping abilities and the emergent reaching coordination pattern that occurs as cube size is varied. SUMMARY: Therapeutic use of the PAF requires new examination and intervention strategies predicated on the development of unitless ratios for functional human actions. Key Words: perception-action; stroke, motor control, unitless ratio.