Effect of patterns of shock and nonshock training trials on response alternation and extinction in escape training

Effect of patterns of shock and nonshock training trials on response alternation and extinction in escape training* JOSEPH J. FRANCHINA Virginia Polytechnic Institute and State University, Blacksburg, Va. 24061 and C. R. SNYDER Vanderbilt University, Nashville, Tenn. 37203 Escape behavior was trained under 100% shock schedules or 50% schedules of shock and nonshock presented in single·alternation, random, or counterbalanced sequences. Terminal acquisition was highest for 100% shock. For 50% schedules nonshock trial performance was reliably slower for alternation than for random or counterbalanced sequences; shock trial performance showed no reliable pattern effects. In extinction, performance on early trials decreased reliably for all groups except the 50% alternation group. Nonspatial alternation of fast and slow floor was of steel rods wired to a responding based on alternating reward and constant-voltage source (dc) for 50-V nonreward has been weil documented for shock. The safe box floor was Masonite and appetitive learning (e.g., Bloom & Capaldi, could be depressed by S's weight to act as a 1961). The present experiment investigated switch. l11umination in each box was whether nonspatial alternation would constant at 7 fc. SUBJECTS, DESIGN, occur in aversive conditioning (escape AND PROCEDURES training), based on alternating the presence F orty-eight naive female Holtzman and absence of a primary motivator electric shock. Accordingly, escape behavior was albino rats, 100·110 days old, received s tudied under single-alternation (SA), 2 days of exploration of the apparatus at random (R), and counterbalanced (C) 50% 16 min per day. On Day 3 Ss were schedules of shock and nonshock. Evidence randomly and evenly assigned to 100, for alternation was SA group's responding 5OSA, 50R, or 50C groups for 10 days of faster on shock and slower on nonshock escape training at 16 trials/day. Group 100 trials than R or C groups. A had shock on all trials. The 50SA, 50R, between·groups evaluation of alternation and 50C groups had shock and nonshock was used instead of the more usual trials intermixed on a 50% basis in within·S approach of appetitive studies alternation, random, and counterbalanced (e.g., Bloom & Capaldi, 1961) to avoid sequences, respectively. Each 50% group confounding stimulus-intensity effects with had the same equal number of daily shock sequential trials effects of shock and and nonshock trials. For 50SA nonshock presentations. Nonshock trial odd·numbered trials were nonshock, performance has been frequently reported even·numbered were shock. (e.g., Franchina, 1969) as reliably slower For a shock training trial S was placed than shock trial performance. Thus, into the startbox and 10 sec later the nonspatial atlernation, demonstrated guillotine door was raised, simultaneously within S under SA, might be attributed to activating shock and a .Ol-sec unit timer.1f differences in relative stimulus in tensity S jumped the hurdle, the safe box floor between shock and nonshock trials rather depressed, stopping the timer. Ten seconds than to SA sequential effects. . later S was removed to its horne cage for a Between-groups comparison of SA, R, and 90-sec ITI. If S failed to jump the hurdle C on shock and on nonshock trials within 40 sec, the shock was kept on, S separately provided that stimulus intensity was removed from the startbox to the was held constant while the effects of horne cage, and a latency of 40 sec was shock-nonshock sequences were evaluated. recorded. Nonshock trials followed these procedures, except that shock was omitted. APPARATUS Extinction with nonshock began on the The apparatus was described in detail by Franchina (1968). Briefly, a white startbox day after training ended. To minimize the was se para ted from a black safebox by a possible decremental effects of a guillotine door and a hurdle. The startbox between-day shift from acquisition to extinction, Trials 1-4 on Extinction Day 1 were training trials administered to each 'These data were collected at Southern group under its appropriate schedule. Methodist University. Psyehon. Sei., 1970, Vol. 21 (3) Extinction trials comprised the last 12 trials of Day land 16 trials/day for the next 3 days. These nonshock trials were conducted exactly as in training. All performance measures were converted to reciprocals of latency. RESULTS Training Since the alternation data are of primary interest, the effect of training schedules on terminal performance will be mentioned briefly. Grand mean reciprocals of latency on the last training day (16 trials) were 2.00, 1.77, 1.72, and 1.31, for 100, 50R, 5OC, and 50SA, respectively. (Shock and nonshock data were combined for 50% groups.) Thus, terminal acquisition level increased with shock percentage (100 over all 50s) and with irregularity of 50% sequences. Analysis of variance over all groups yielded a reliable groups effect (F = 20.65, df = 3/44, p< .001). Scheffe comparisons yielded reliable differences between each pair of groups (p< .005) except 50R vs 50C (p > .10). Considering alternation, Fig. I presents the results of 5OC, 50R, and 50SA on shock and on nonshock trials. Evidence for alternation occurred on Nonshock Trial Blocks 21-40; 50SA was slower than 50R and 50C (F = 48.55, df = 2/33, p< .001). Evidence for alternation failed to occur on shock trials; the groups performed similarly to each other. Analysis of variance over Trial Blocks 21-40 yielded a groups F = 1.33, df = 2/33, P > .20). F or interest, shock trial performance of 50% groups was compared with that of Group 100 over Blocks 21-40. No reliable groups effect occurred (F = 1.05), suggesting that interspersing nonshock among shock trials for 50% groups did not impair shock trial performance. Comparison of shock with nonshock trials for each 50% group reliably showed the frequently reported (e.g., Franchina, 1968, 1969) inferiority of nonshock performance (ps< .001). Extinction Figure 2 presents the performance of each group for the four training trials on Extinction Day 1 (ACQ, unattached points) and for all extinction trials. ACQ shows performance highly similar in appearance and statistical reliability to terminal acquisition levels reported earlier and, consequently, will be considered an index of such. For 50% groups ACQ represents the combined data of shock and nonshock trials. Mean shock trial performance for 50R, 5OC, and 50SA on ACQ was 1.80, 1.75, and 1.70, respectively, mean nonshock trial performance was 1.60, 1.40, and .68, respectively. Comparison of 50% groups performance between ACQ nonshock trials 177 2.00 1.90 .50R ::: SOC :: SOSA 1.80 2 . 10 1.70 2.00 1.60 1.90 • ~ ~ 1.40 io 1.70 • 1.30 : 1.60 Cl ~ -' C1. 20 >- 1.50 Z u <I; >~ 1.30 ~ 1.40 ~ 1.1 0 .J 1.00 0 .90 ... 120 o '"<I; .80 0 .70 v ... ~ .90 '"CL .60 8 .50 !i! .80 '" '" .70 z ~ .60 Z .40 <I; ~ .30 .20 .50 .10 .40 and Trial Block I of extinction revealed a nons (...truncated)