Acquired drive strength as a joint function of UCS intensity and number of CS-UCS pairings.

The form of the empirical law relating acquired drive strength to UCS intensity and number of CS-UCS pairings was investigated in two experiments using 120 and 30 male albino rats, respectively. Strength of UCS was varied at a broad range of intensities. Controls were introduced to prevent the intrusion of competing crouching responses (R1) on the measurement of response strength (R2). Acquired drive strength was found to be curvilinearly related to UCS intensity and number of CS-UCS pairings during conditioning. The relationship was monotonic and negatively accelerated. Habit strength, or sHr, was found to be jointly determined by UCS intensity (D) and number of CS-UCS pairings during aversive conditioning. These results were contrasted with findings for the instrumental appetitive learning case of Hull's system, where it has been shown that sHr and D are independent and interact in a multiplicative fashion in their effect on performance. An historical review of acquired drive experiments was also presented.