The behavioral field approach employs naturalistic observation and simultaneous, multiple recordings of ecologically relevant aspects of behavior-environment interactions. Applying this approach to runway learning in the rat, the inferior acquisition speed of partial reinforcement (PRF) subjects as compared to continuous reinforcement (CRF) subjects was found to result from greater response variability, more sniffing and goal-avoidance behavior, and slower dropping out of collateral behaviors (e.g., drinking and sand-digging). Extinction first produced an increase in exploratory behavior, then displacement activities (e.g., grooming and biting) and goal-avoidance. CRF subjects showed greater response persistence as measured by number of extinction trials to disrupt an established, favored path. PRF subjects showed greater goal persistence as measured by trials to retrace from goalbox. In extinction, while CRF subjects were more inclined to engage in drinking and sand-digging in the startbox. PRF subjects exhibited more biting behavior in the goalbox. The only sex-related differences were superior speeds by female CRF subjects, inferior goal speeds by female PRF subjects during acquisition, and superior goalbox escape learning by females in extinction.The behavioral field approach to instrumental learning may be characterized by naturalistic observation and simultaneous multiple recordings of ecologically relevant aspects of behavior-environment interactions in a testing situation that permits the display of speciesspecific behavior; its focus of analysis is on the interrelationship between the designated instrumental response and other responses observed in the testing situation.In contrast to the behavioral field approach, the traditional research strategy in animal learning calls for the arbitrary isolation of a small segment of environment (the stimulus) and a small segment of behavior (the response) and the analysis of functional relationship between them. To achieve this end, researchers typically employ a simple, straight runway or a barren operant chamber equipped with a protruding lever or a lighted key. In this simple-parts approach, highly complex behavioral phenomena are reduced to the analysis of some simple stimulus-response relationship quite arbitrarily chosen on the basis of convenience in manipulation and quantification. But focusing on simple parts