Effect of intertrial reinforcement and nonreinforcement on reversal learning)

Two experiments were run. In the first, 33 rats learned a black-white discrimination and were then reversed. Eleven Ss received an ITR in the acquisition goal box before each reversal trial. Eleven Ss received ITR in the reversal goal box, and 11 got. regular reversal. The second experiment was exactly the same except Ss received ITNR instead of ITR. The only significant difference was that Ss receiving ITNR in the acquisition goal box reversed faster than their controls.

Stein (1957) manipulated reward independently of the instrumental response, and Trapold & Doren (1966) manipulated nonreward independently of the instru­mental response. Neither observed an effect on per­formance in the straight alley. The question in the present study was whether rewarding and nonrewarding events which occur independently of the instrumental response during reversal training would affect re­versal performance. Experiment I

The Ss were 36 experimentally naive Wi star strain albino rats, approximately 90 days old at the beginning of training.

The apparatus was an enclosed wooden T maze 4 in. wide, 5 in. deep, and covered with hinged hardware cloth. The floor of the maze was also constructed of hardware cloth. The stem of the maze was 36 in. long and painted a mid-gray. One black, one white, and one gray arm, 16 in. long, were mounted on run­ners on either side of the stem. A tin feeding cup 2 in. x 2 in. x 2 in. was fastened at the end of each arm. Guillotine type doors placed at the entrance to the arms prevented retraCing.

Twenty-three hours after food had been denied the Ss, they were handled in groups of 12 for 30 min. each. Wet mash was available on the handling table. All Ss were fed wet mash for 1 hr. in their home cages after handling. The same treatment occurred the first four days. On the fifth day, Ss explored the apparatus in groups of four for 15 min. before feeding. The arms of the T maze were gray during exploration.

The E divided Ss into three equal groups by means of a random numbers table. Each group was then randomly divided into two equal subgroups. Half of each group learned to choose the black arm, the others the white arm. The E determined the position of the white (black) arm by means of a random num­bers table with the stipulation that the position of the arms could not remain the same more than three suc­cessive trials. The Ss received five trials each day.

Psychon. Sci., 1967, Vol. 7 (3)

JAMES BOWEN ARLINGTON STATE COLLEGE OF THE UNIVERSITY OF TEXAS

The goal box confinement period was 15 sec. whether S chose the correct Or incorrect arm. The reward was wet mash made from equal part (by volume) of water and ground Purina Lab Chow. The Ss were run in squads of six, and the intertrial interval was about 3.5 min.

The Ss were trained to a criterion of nine of 10 correct choices. One S failed to reach criterion and was eliminated. The S with the most errors from each of the other groups was then eliminated to maintain equal groups.

Reversal training was begun for each S the day after it reached acquisition criterion. One group re­ceived regular reversal training (Group C). Another group received a 15-sec. ITR (Intertrial Reward, Le., S was placed directly into the goal box and allowed to eat) in the reversal goal box about 1 min. before each trial (Group ITR-R). The third group received a 15-sec. ITR in the acquisition goal box about 1 min. before each trial (Group ITR-A). The Ss were reversed to a criterion of nine of 10 correct choices. The inter­trial interval was about 6 min. Experiment II

The Ss were 36 experimentally naive Wi star strain albino rats, approximately 90 days old at the beginning of training. The Ss received the same pretraining, acquisition, and reversal in the same apparatus as the Ss in Experiment I except that the experimental groups received ITNR (Intertrial Nonreward) instead of ITR. Results and Discussion

The mean number of errors to reach the acquisition criterion were 7.3 for Group ITR-R, 7.7 for Group C, and 7.7 for Group ITR-A. The differences were not significant, F=.06, df=2/30.

As illustrated in Fig. 1, the performances of the three groups during reversal were very similar. Anal­ysis of the errors made during the first five reversal trials indicated that the differences were not signifi­cant, F = .97, df = 2/30. The mean number of errors for Group ITR-R was 2.82, for Group C, 3.00, and for Group ITR-A, 3.36. With a = .10, use of Duncan's Multiple Range Test showed nonsignificant differences among the means. If errors before the first success, errors in the first 10 reversal trials, or errors before reaching reversal criterion are analyzed, the same results obtain.

The mean number of errors made in acquisition were 6.1 for Group ITNR-A, 6.3 for Group C, and 6.9 for Group ITNR-R. The differences in errors were not Significant, F= .22, df=2/33.

93

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e-e Gp ITR-R 0:: .9

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Fig. 1. Experiment I: Probability of an error during reversal training.

The mean number of errors during the first five reversal trials for Group ITNR-A was 2.33, for Group C, 3.50, for Group ITNR-R, 4.08. An analysis of the data indicated that some differences were significant, F=10.9, df=2/33, p< .005. Use of Duncan's Multiple Range Test indicated that Group ITNR-A differed sig­nificantly from Groups C and ITNR-R, (p< .01). The latter groups did not differ dependably with Cl' = .10. This difference is shown in Fig. 2. If errors before the first success, errors in the first 10 reversal trials, or errors before reaching reversal criterion are analyzed, the same results obtain.

The results, then, indicate that ITR in either goal box and ITR in the reversal goal box do not affect reversal performance, while ITNR in the acquisition goal box enhances reversal performance. It is not

94

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LL .6 0

.5 >-I- .4 :J .3 Ci5 <{ .2 (D

0 0::

.1 0... 0

_. Gp ITNR-R 4--4 Gp C 0-'-0 Gp ITNR-A

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Fig. 2. Experiment II: Probability of an error during reversal training.

clear from these data, however, whether previous rewarded experience in the negative goal box is necessary before ITNR will enhance performance, since ITNR in the negative goal box might facilitate acquisition as well as reversal.

References Stein, L. The classical conditioning of the consummatory response

as a determinant of instrumental performance. J. compo physio/.

Psycho!.. 1957, 50, 269-278. Trapold, M. A., & Doren, D. G. Effect of noncontingent partial rein­

forcement on the resistance to extinction of a runway response. J. expo Psycho/" 1966, 71, 429-431,

Note 1. This research was supported by Public Health Service Research Grant MH 10041-01 from the National Institute of Mental Health.

Psychon. Sci., 1967, Vol. 7 (3)