1. a temporary readiness to perform certain psychological functions that influences the response to a situation or stimulus, such as the tendency to apply a previously successful technique in solving a new problem. It is often determined by instructions but need not be. Essentially synonymous with the older term Einstellung, mental set is the embodiment of the earlier concepts of Aufgabe and determining tendency.

2. the situation in which a preparedness to perform one type of task causes a decrement in the ability to perform on some other category of task. See task switching.