US-US conditioning of the rabbit’s nictitating membrane response: Emergence of a conditioned response without alpha conditioning

Two experiments were conducted to examine whether classical conditioning of the rabbit’s nictitating membrane response (NMR) could be obtained when paraorbital electrical stimulation served as both the conditioned stimulus (CS) and the unconditioned stimulus (US). In Experiment 1, a range of stimulation intensities (0.1, 0.25, 0.5,1, and 2 mA) and durations (10, 25, 50, and 100 msec) were presented in order to detail the frequency, latency, amplitude, and duration of unconditioned responses (URs) to the paraorbital US. On the basis of the response characteristics obtained in Experiment 1, a set of stimulation values was adopted in Experiment 2 to (1) examine whether classical conditioning could be obtained when paraorbital electrical stimulation served as both the CS and the US, and (2) determine whether conditioning was related to the intensity of the CS. The data from Experiment 1 indicated that response frequency, amplitude, duration, latency, and peak latency were a function of stimulus intensity and duration. The results of Experiment 2 revealed significant levels of conditioned responding that emerged as a function of CS-US pairings. There were no systematic changes in the UR to the CS as a function of CS-US pairings. Moreover, the levels of conditioning obtained using a paraorbital CS were a function of CS intensity. The results are discussed in terms of the relevance of US-US conditioning studies to contemporary theories of associative learning and the search for the neural substrates of learning and memory.