The Effect of the Interpolated UCS Alone Trials on Classical Aversive Conditioning

Three groups of 15 Ss each were given 60 trials in an eyelid conditioning experiment. The control group (GC) received 60 pairings of CS and UCS in the normal conditioning procedure. One of the experimental groups (GE1) received only the 'UCS during Trials 21~0 (massed), the ether (GE2) 20 UCS alone trials interspersed among the first 40 trials (distributed). These trials were arranged in a 2:1 variable ratio schedule. Not any signal before trials is used in order to avoid the possibility of interference. The results showed that the performance of the control group was significantly greater than that of the experimental groups over the last 20 conditioning trials. Since the drive level (D) of the three groups was presumably equated, the performance difference was taken as evidence to support the traditional Hullian theory that the response strength is a multiplicative function of learning factor (H) and drive level (D) rather than to support Kimble's notion of pseudoconditioning and the rapid growth of H factor. The mean percentage of CR of the control group on Trials 21-40 is also significantly superior to that of the two experimental groups on Trials 41-60, where all three groups received the same number of CS-UCS pairing, but the experimental groups had 20 other UCS alone trials added to their trials. It abo supports the Hullian theory of the gradual increasing of the H factor. GE1 and GE2 received the same number of CS-UCS pairings (equal H factor) and UCS alone trials (equal D factor) but GE1 is inferior to GE2 over the last 20 trials. The result suggests that the pattern of the distribution of the interpolated UCS alone presentation is also an important factor in classical aversive conditioning..