Intertrial Interval Range Shift in Classical Eyelid Conditioning

Abstract

Prokasy and Whaley (1961) gave 1 2 human Ss extensive training in the classical eyelid conditioning situation, where the independent variable was the set of ITIs (intertrial intervals) of 5, 10, 15, 20, 25, and 30 sec. They were interspersed in an unpredictable order over 679 uials administered in seven sessions. It was found that probability of response following the different 1TIs did not vary as a function of ITI. This result was interpreted as incompatible with the hypothesis that response-produced inhibition (Hull, 1952, p. 9) explains the superiority of spaced to massed practice obtained in earlier classical eyelid conditioning studies (e.g., Spence & Norris, 1950; Prokasy, Granc, & Myers, 1958) . It was the purpose to test other implications of the response-produced inhibition hypothesis. Specifically, if inhibition is assumed to cumulate with massed trials, then a later switch to spaced trials should result in an increase in response probability. Similarly, after training with relatively spaced trials, a shift to massed trials should result ic, a decrement in response probability. PROCEDURE The apparatus is described in Prokasy and Whaley ( 1 9 6 1 ) . The CS was a brightness change of 3.8 to 190 mL. lasting 500 msec. The UCS, a 50-msec. puff of nitrogen, was delivered to the right cornea from .75 in., and was of sufficient intensity to support a 210-mm. column of mercury. The interstimulus interval was 500 msec. Ss were 27 male students between the ages of 18 and 22, who received course credit in introductory psychology for volunteering. One was terminated due to failure to condition; 2 failed to complete the training sessions because of end-of-semester scheduling problems. Two IT1 ranges were selected: a massed range including ITIs of 5, 10, 15, and 2 0 sec., and a spaced range including ITIs of 20, 25, 30, and 35 sec. The 24 Ss were assigned at random to two groups. Group MS received 5 sessions of 65 trials each with the massed IT1 range followed by 5 sessions of 65 trials each with the spaced IT1 range. Group SM received the spaced range for the initial 5 sessions and the massed range for the final 5 sessions. In all sessions, with both ranges, the 4 lTIs were administered in a pre-determined, unpredictable order, with the resrrlcuon that each IT1 appear 1 6 times in each session and that no one IT1 follow itself more than once. Thus, across the 10 sessions Ss in Group MS received each of the 4 massed ITIs 8 0 times each, followed by each of the 4 spaced ITIs 8 0 times each. Ss in Group SM received the same treaunent except that the 5 spaced sessions preceded the 5 massed sessions. Instructions were read S ac the beginning of Session 1. S was given neutral instructions which indicated that he should not try to control his responses in any way and that he should keep the CS panel in view at all times. In subsequent sessions Ss were reminded of instructions informally. Although it was not possible to run Ss on 1 0 consecutive days, rarely was there a break between sessions of longer than 3 days.