Final answer:
The concept that enables alteration of movement attributes like speed and amplitude to suit task demands is known as 'parameter value' within a generalized motor program.
Step-by-step explanation:
The concept that allows a person to change features such as speed and amplitude to meet the environmental demands of a task is known as the parameter value setting within a generalized motor program (GMP). GMPs are part of motor learning and control theory and explain how we are able to perform movements in varying conditions without having to learn a new movement pattern each time.
For example, when throwing a ball, you can modify the speed and force of the throw (parameters) without altering the overall motion pattern. This flexibility is essential in adapting motor skills to new situations.