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‘Abnormal fixations’ and ‘learned helplessness’: Inescapable shock as a weanling impairs adult discrimination learning in rats
‘ABNORMAL FIXATIONS’ AND ‘LEARNED HELPLESSNESS’: INESCAPABLE SHOCK AS A WEANLING IMPAIRS ADULT DISCRIMINATION LEARNING IN RATS* JUDY
GARBER,?ELLEN FENCIL-MORSE,ROBERTA. ROSELLINI and MARTIN E. P. SELIGMAN Department of Psychology. University of Pennsylvania. 3815 Walnut Street. Phiiadelphi~ PA 19104, U.S.A. (Receiced 3 Junuars 1978)
Summary-Weanling rats received escapable, yoked inescapable. or no eiectric shock. Tested as aduhs. the inescapable groups were poor at appetitive discrimination teaming in either a parallel arm maze (Experiment I) or a Lashley jumping stand (Experiment 2). They were slower to respond. slower to reach criterion. made fewer correct responses and more non-responses than the escapable or no shock groups. We suggest that rats retain learned helplessness from weaning to adulthood. that such learning generalizes widely and that learned helplessness may explain the abnormal fixation results of Maier (1949).
This paper asks three questions: (a) is learning about uncontrollability retained from weaning to adulthood in the rat? (b) does this learning generalize from inescapable shock to appetitive di~imination learning? and (c) what is the relationship between the ‘abnormal fixations’ of Maier (1949) and ‘learned helplessness’ (Se&man. 1973 Adult dogs, rats and humans exposed to inescapable electric shock show marked deficits in later escape learning, whereas animals exposed to equal amounts of escapable shock show no such deficit. Learning deficits resulting from experience with inescapable shock and the hypothesized mediating process, learning that outcomes are independent of responding, have been dubbed ‘learned hetplessness’ (see Maier and Seligman, 1976; Seligman, 1975, for a review). Recently, Hannum et al. (1976) found shock escape deficits in adult rats even when inescapable shock was given 60 days previously, shortly after weaning. This paper reports deficits in adult appetitive discrimination learning resulting from inescapable shock received as a weanling. How general across different motivational states is interference produced by inescapable shock in the rat? Inescapable shock in adult rats interferes with learning to escape frustration produced by nonreward (Rosellini and Seligman, 1973, with learning a free operant bar press for food (Rosellini, unpublished manuscript), with learning underwater escape (Altenor et al, in press), and with shock-elicited aggression (Maier er al., 1972). So, interference produced by inescapable shock appears quite general to other tasks in adult rats. The present experiments extend the generality to complex discrimination learning for food and show that the deficit can be produced even when the original learning takes place early in life. We found that inescapable shock impaired discrimination learning, and the observed deficits were reminiscent of Maier’s (1949) ‘abnormal fixation’ data. Learned helplessness has been posed as a model of depression; it has also been suggested that helplessness may underlie other forms of maladaptive behavior, such as abnormal fixations, as well (Seligman, 1975). We suggest below that learned helplessness may be the basis of the phenomenon observed by Maier. * This study was supported by National Institute of Mental Health Grant (MH 19604) and a Guggenheim Fellowship to M. E. P. Seligman and National Institute of Mental Health Postdoctoral Fellowship (MH 00980-02)Vto R. A. Roseflini. Request for reprints should be sent to M. E. P. Seiigman, Department of Psychology, University of Pennsylvania, 3815 Walnut Street, Philadelphia, PA 19104, U.S.A. t Now at Psychology Dept.. University of Minnesota, 7.5 East River Road. Minneapolis, MN 55455,U.S.A. 197
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Method Subjects. The subjects were 24male Holtzman rats, 25 days old and weighing 64-77 g on the first day of pretraining. They were singly housed, maintained on a6 lib. food and water, and were run during the light phase of the 12 h dark/l2 h light cycle. Apparatus. Shock training. Shock was administered in jump-up boxes 23.5 cm long, 20.0 cm wide and 20.0 cm high. The end walls were constructed of stainless steei, the side walls and roof of clear Plexiglass. The floor consisted of stainless steel grids 0.4 cm in diameter, spaced 1.5 cm apart. The box was illuminated by a 75 W bulb mounted 13.0cm above the floor in the center of the end wall opposite the platform. Shock of l.OmA intensity was delivered to the animal by a constant-current shock source consisting of a 600 V (A.C.) transformer and a limiting resistor. An electrode lead entered through the ceiling of the chamber and was attached to a safety-pin electrode mounted subcutaneously in the animal’s upper back. The shock circuit was completed through the grid floor. Shock pulsated at a rate of 5 cps, with an equal on/off cycle. A trial began with the delivery of shock and with the upper ll.Ocm of the platform end-wall sliding back to expose the 20.0 cm wide and 12.5 cm deep platform. The platform was electrified on each trial for the inescapable group and was nonelectrified for the escapable group. When the animal jumped on to the platform, shock terminated for animals in the escape group and. for their yoked inescapable partners. If the animal failed to escape, shock remained on for 6Osec. White masking noise was present during the experimental sessions. Discrimination learning. A parallel arm maze was used for discrimination testing when the rats reached 100 days of age. The maze consisted of a 13.Ocm long start box, a 26.0 cm long runway to the choice-point area, and two 35.Ocm goal boxes placed parallel to one another with the sides touching; the choice-point area between the runway and the goal boxes was 26.Ocm long and 8.0 cm wide. The walls of the maze were constructed of unpainted plywood and the floor consisted of moisture-resistant disposable brown paper over a plywood base. The maze was covered by a clear Plexiglass lid and illuminated by two 75 W bulbs mounted in the ceiling of the room, each bulb 165.Ocrn from the maze, one 35.0 cm in front of the start box and the other 35.0cm behind the ends of the goal boxes. A timer was activated as the guillotine startbox door was raised. Photocells located 4.0 cm in front of the startbox and 4.5 cm from the ends of each of the goal boxes measured start and goal latencies. A 4.0cm long, 2.5 cm wide and l.Ocrn high food cup was mounted on the endwall of each goal box and rested on the floor. Plexiglass guillotine doors separated the runway from the start box and the choice-point area from the goal boxes. Black and white stimulus cards covered the entire wall surface inside the goal boxes; one card had a 3.Ocm wide horizontal stripe pattern, the other, a 3.0 cm wide vertical stripe pattern. The stimulus patterns were visible from the choice point. Food was consistently correlated with one stimulus pattern and absence of food with the other (counterbalanced). ~xperi~e~tu~ design. Three groups were used, one experimental and two control. Beginning with jump-training at 25 days of age, the experimental group received inescapable shock (Group Y, N = 8) yoked for the same pattern and duration to an escapable shock control group (Group E, N = 8). The other control group was not shocked (Group 0, N = 8). Four shock sessions were given, one every third day until the rats were 34 days old. At 100 days of age, all animals received discrimination testing in the parallel arm maze. Correct responses were rewarded with ten 45 mg Noyes food pellets; incorrect responses were not rewarded. Procedure Shock training. Jump-up shock escape training began at 25 days of age. The shock training procedure was similar to that employed by Hannum et al. (1976). Prior to the first training session each animal’s back was shaved from the neck to the tail to
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prevent the attenuation of shock by rolling on its back, and each subject was weighed. Escape training consisted of exposing the animals in Group E to 60 trials of l.OmA shock, which could be escaped by jumping up on the platform. Shock onset and the availability of the platform were simultaneous. This procedure resulted in consistent escape in all Group E animals by the end of training. Each animal in Group Y was yoked to animal in Group E so that each pair received identical durations and patterns of shock. Shock was therefore inescapable for the Group__Y animals, since its termination was controlled by the animals in the escapable group. Shock was given on a variable interval 1-min schedule with a range of 15-105 set; the shock session was approximately 60 min long. Animals in Group 0 (nonshocked controls) were also shaved, implanted with a subcutaneous safety pin electrode and placed in operant chambers for the same amount of time, but were not exposed to shock. Discrimination learning. Following shock training, all animals were maintained on ab lib. food and water for the next 64-66 days. During this period animals were not handled. At 100-102 days of age animals were placed in the parallel arm maze and habituation training began. On trial one of the first day of habituation, each animal was placed in the start box of the runway with the guillotine to each of the goal boxes raised; the start box door was then raised and the animal was allowed to explore the maze for 3 min. On the next two habituation trials of the first day, the animals were placed in the right-hand goal box for one trial and in the left-hand goal box for the other trials; all guillotine doors were raised. The fourth trial was a repetition of the first trial. Each animal received four trials per day on four different days. On day three of habituation, total food deprivation began until the animals reached 85% of their free-feeding body weight. They were then maintained on 850/, fixed body weight deprivation schedule (Weinstock, 1972). The range of initial body weights for the three groups was 31 l-394 g. The order of box placement changed systematically as follows: day l/start box (S), right goal box (R), left goal box (L), start box (S); day Z/RLSR; day 3/LSRL; day 4/SRLS. Habituation days were nonconsecutive, two days of rest intervening between habituation days 2 and 3, and three days between 3 and 4. During habituation, stimulus cards were randomly switched from the right to the left goal box and vice versa. On day 1 of maze training each animal was given ten 45 mg Noyes food pellets prior to trial 1 in the home cage. During the 15 consecutive days of maze training each animal received 10 trials per day. On each trial the animal was placed in the start box, facing the goal, and the guillotine door to the start box was raised. After the animal entered the goal box the guillotine door was lowered to prevent retracing. The horizontally striped goal box choice was reinforced for half the animals; the vertically striped goal box choice was reinforced for the other half. Reinforcement consisted of ten 45 mg Noyes pellets in the goal box food cup. On incorrect trials the animal waited in the foodless goal box for 30 set before being replaced in its home cage. Animals were always run in the following order: El, Y,, C,, El, Y,, C1, E3.. . . The intertrial interval was approximately 30 min. RESULTS Shock
AND
DISCUSSION
training
All animals in Group E learned the escape response. No failures to escape were observed in this group during the last 20 training trials. The mean amount of shock received by Groups E and Y was 668.44sec with a standard error of 649.70sec. Discrimination
learning
The inescapable group did poorly at discrimination learning whereas the escape and nonshocked groups did well. Maze performance showed the typical acquisition curves of increasing percent correct per day over the first 13 days of training with asymptotic performance on days 13-15 for Groups E, Y and 0. Figure 1 presents the per cent
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Fig. I. Mean
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correct over days for the three groups. A 3 x 15 repeated measures analysis of variance showed significant differences among the three groups throughout training, F (2,21) = 4.43. p < 0.025; a significant effect of days TF (14,294) = 31.8, p < O.OOl]; and no significant groups x days interaction, F < 1. Newman-Keuls posr hoc tests showed both Groups E and 0 to have higher per -ctmt correct than Group Y (p’s < 0.05). Groups E and 0 did not differ significantly in percent responses correct across days. Similarly, the groups differed significantly on the number of trials to reach the SO”/:, correct criterion (80% correct responses during a single day of discrimination trials) [F (2, 21) = 7.125, p--c 0.011. Newman-Keuls post hoc tests showed that Group E (mean = 59.57) took fewer trials to reach criterion than Group Y (mean = 107.0) @ < 0.05). Group 0 (mean = 78.0) did not significantly differ from either Group E or Group Y. Did the yoked animals develop more persistent position habits than the escape or control animals? Systematic response tendencies (hypotheses) were examined using a method suggested by Krechevsky (1932) and Levine (1975). For each rat the following items were determined: (1) number of ‘errors’ the animal made each day; (2) the number of jumps to the left; (3) the number of juinps to the right: and (4) the number of jumps in keeping with an ‘alternating’ scheme.* The groups differed si~i~cantly for the total number of days on which ‘systematic’ behavior was observed [F (2,19) = 8.57, p -C 0.011. Newman-Keuis post hoc analyses revealed that animals in the yoked group (mean = 6.28 days) responded in a systematic manner (universally position habits) significantly longer than both the escape (mean = 2.57 days) and the control (mean = 3.0 days) animals (p < 0.05). Four animals (three from Group Y and one from Group 0) maintained a position habit over the entire course of the experiment and thus failed to reach the 80% correct criterion of correct responses. The remaining animals typically showed a brief period of random sampling prior to attaining the criterion. Thus it may be that this transition from position habit to the appropriate discriminated response is delayed or prevented by exposure to inescapable shock, resulting in the observed Group Y deficit in correct responding. This deficit, particularly the failure to give up a position preference, is reminiscent of Maier’s (1949) abnormal fixation results and those of Bainbridge (1973). Maier found that rats exposed to unsoivable discrimination problems in a Lashley jumping stand subsequently failed to learn when the problems were made solvable. They typically showed ‘fixated’ behavior, responding consistently to one side only. Would inescapable
* From these data a series of ‘learning’ curves were plotted for each rat. To determme if the appearance of systematic responses. e.g. position preference, was a chance fluctuation, following Krechevsky (1932). we used the criterion of k2.5 SD. from chance [where SD. = ,/(PQ/N)]. For this study, this meant that responding to one side on at least 90 per cent of the trials constituted a significant position bias.
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shock given to weanling rats produce similar deficits at adult discrimination learning on a Lashley jumping stand? Experiment 2 attempts to replicate and extend the results of Experiment 1 to a different kind of apparatus. Three groups of weanling rats received escapable, inescapable, learning task on the Lashley or no shock and were tested on an appetitive discrimination jumping stand. EXPERIMENT
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Method Subjects. The subjects used were 24 male Sprague-Dawley rats, received from the Holtzman Company when they were between 22 and 24 days of age. They were singly housed. maintained on ab lib. food and water, and were run during their light phase of the 12 hr dark/l2 hr light cycle. Apparatus. The same pretraining apparatus described in Experiment 1 was used. Discrimination testing. The appetitive discrimination apparatus was a modified Lashley Jumping Stand. It consisted of three-ply pine, 91.44 cm wide and 152.4 cm high, having two 14cm square holes cut 76.2 cm from the floor and spaced 5 cm apart. Attached to the back of the screen, 0.64 cm below the lower edges of the openings was a 30.5 cm platform on which food was placed. A starting platform, 25 cm in diameter, from which the animal jumped was placed in front of the middle of the screen. The distance between the stand and the screen varied systematically and is outlined in the procedure. A projecting sheet of metal served to deflect the rat through the openings in case he jumped too high. A 5 cm thick piece of foam rubber 45 cm wide and 91.44 cm long was placed below subjects in case of a fall. The openings were fronted with 15.2 cm squares of heavy cardboard upon which the horizontal and vertical discrimination patterns were drawn. One card bearing the negative stimulus was fixed rigidly by a metal door; the other card was left unfastened to allow the animal to jump against it and project his way through to the platform. Experimental design. Groups of eight triads were given training with either escapable, inescapable, or no shock shortly after weaning, and tested on an appetitive discrimination learning task as adults. A triad consisted of one rat receiving escapable shock (Group E), a yoked rat receiving the same pattern and duration of shock as his partner (Group Y), and a third rat receiving no shock (Group 0). The animals were randomly assigned to the three training conditions. Procedure Shock training. The shock training procedure was the same as that outlined in Experiment 1. Appetitioe discrimination tesr. At 110-112 days of age all animals were placed and then maintained on an 85% fixed body weight deprivation schedule (Weinstock, 1972) for the duration of the experiment. The range of body weights for the three groups was 330-343 g. Preliminary discrimination training. Before beginning testing on the appetitive discrimination apparatus all animals were given three training days of 10 forced trials-five trials to each side according to a Gellerman (1933) order. On each trial the subject was required to go through one of the windows to the platform where they received five pellets of food (45 mg Noyes food pellets). The first day of training consisted of 3 min of exploration of the apparatus and exposure to the food. The jumping stand was adjacent to the open windows of the apparatus so the animal could walk across to the feeding platform. On the following two days they were given training in jumping from the stand through the open window in the screen to the feeding platform. This was done by retracting the stand back approximately 2.5 cm per trial from a position adjacent to the screen to a position 22.9 cm from the screen. On day 3, animals were trained to jump at and knock over the stimulus cards. One card had horizontal black
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and white lines (2.0cm wide). Cards were alternated from side to side according to a selected Gellerman order. The cards readily fell over whenever struck by the rat. To prevent the animal from jumping CotisistentIy to one side or one of the cards. manual guidance was introduced whenever the animal began to express a preference for one side or one card. This guidance consisted of pushing the rat away from the preferred window or card as soon as it prepared to jump. Discriminariun training. Beginning on the fourth day all animals were exposed to the visual discrimination problem in which the vertical card and the horizontal card were alternated from side to side according to the selected orders. Vertical was consistently locked for one-half of the animals in each group while horizontal was consistently locked for the other half. Responses to the unlocked stimulus were correct and were followed by five food pellets. Responses to the locked stimulus were incorrect and resulted in the animals falling to the foam rubber below. A ‘nonresponse’ was defined as the animal’s failure to jump within 180sec of being placed on the stand. Subjects received a total of 10 trials a day for 15 days. On each trial the animal was placed on the jumping stand, which was set at 12.7 cm from the screen for all test trials, until he responded or 180sec had elapsed, without a response. Correct, incorrect and nonresponses were recorded as well as latency to respond for each trial. Using a stopwatch, the experimenter recorded the latencies to the nearest tenth of a second. RESULTS
Shock
training
All animals in the escape group learned to jump onto the platform to terminate shock. No failures to escape were observed for any of these animals on the last 20 trials of training. The mean total amount of shock received by the escape group, and therefore the yoked group as well, was 994.65 set with a standard error of 702.46. Discrimination
test.
Animals receiving inescapable shock shortly after weaning were significantly slower to learn the discrimination as adults than either the escapable or nonshock group. Animals exposed to inescapable shock made substantially fewer mean correct responses per day (Group Y, mean = 7.47) across ‘the 15 days of discrimination learning than rats given either escapable (Group 3, mean = 8.99) or no shock (Group 0, mean = 8.92). A groups (3) x days (15) analysis of variance showed a significant effect for groups [F (2,211 = 5.45, p -z 0.05-J; a significant effect for days [F (14,294) = 36.14, p < 0.001 J; but no significant groups x days interaction, indicating that each group increased nondifferentially in the number of correct responses over days, and that differences existed in the number correct for the three groups. Newman-Keuls post hoc tests showed that Group Y made significantly fewer correct responses than either Group E or Group 0 (p’s < 0.05) which did not differ from each other. The differences in total number of correct responses is infiated by the fact that subjects in the inescapable group made significantly fewer jumps than either the escapable or nonshock groups. The 3 x 15 analysis of variance on number of jumps showed both main effects [F groups (2,21) = 10.5, p < 0.011 and [F days (14,294) = 7.18, p < 0.01) and the groups x days interaction [F (28,294) = 4.97, p < 0.011 to be significant. Newman-Keuls post hoc tests showed Group Y to have made significantly fewer jumps than either Group E or 0 Q’s < 0.01) which did not differ from each other. Figure 2 shows that Group Y initially made fewer jumps, while Group E and 0 jumped on almost every trial from the beginning of testing. Since the difference among the groups on the total number of correct responses is inflated by the fact that the inescapable group emitted significantly fewer responses, the per cent correct of only those jumps made was examined. This analysis attempts to determine whether any deficit over and above the failure to respond exists. Although Group Y (mean = 79.89%) made fewer per cent correct responses per day than Group E
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Fig. 2. Mean
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of jumps for the Escape (E). Yoked (Y) and Control of ten trials per day. Experiment 2.
(0)
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(mean = 90.07%) or Group 0 (mean = 89.74%) this difference showed only a trend toward significance fF (2,21) = 3.15, p < 0.10-j. Newman-Keuls post hoc analyses showed Group Y to have made fewer per cent correct responses for actual resijonses attempted than Group 0 (p c 0.05); Group Y and Group E were not significantly different on this measure (p < 0.10). Figure 3 illustrates that Group Y decreased in mean latency over the 15 days of testing at a slower rate than either of the other groups. The mean latencies for actual jumps made reflected a similar pattern. Animals receiving inescapable shock were signi~cantly slower to respond than either the escapable or no-shock groups [F (2.21) = 6.38, p c 0.011. There was also a significant effect for days [F (14,294) = 22.57. p < 0.011. Newman-Keuls post hoc tests showed Group Y to have significantly longer response latencies than either Group E (p < 0.01) or Group 0 (p < 0.05). These groups did not differ from each other. These last two analyses, however, are not sufficient to establish that any learning deficit is present over and above the motivational deficit in response initiation, The inescapable group. since it made fewer responses per day, had less exposure to the discriminanda-reward contingency. Thus analysis by days rather than by blocks of trials on which responding occurred fails to equate exposure to the learning contingency. We therefore performed two 3 (groups) x 11 (blocks of 10 responses with nonresponses omitted) repeated measures analyses of variance on number correct and latency. These analyses showed that although the yoked group seemed to make fewer correct responses
Fig
3. Mean
latency
in seconds for the Escape (E), Yoked (Y) and Controt blocks of ten trials per day, Experiment 2.
(0)
groups in
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per blocks of ten jumps attempted than the escape or no-shock groups, this difference was not significant [F (221) = 1.57. n.s.1. The yoked group (Group Y, mean = 31.04) was signi~cantly slower to respond, however, than either the escape (Group E. mean = 15.05) or no-shock groups [F (2.21) = 4.20, p < O.OS]. Newman-Keuls post hoc tests showed Group Y to have significantly longer response latencies than either Group E or Group 0 @ < 0.01). These groups did not differ from each other. Thus a deficit in response initiation on the appetitive discrimination learning task appeared in the inescapable group but no deficit appeared in learning the discrimination once we equated for exposure to the contingency. Is the response initiation deficit greater after failure (incorect responses) than success (correct responses)? Groups E and 0 did not differ significantly in number of nonresponses following success vs failure, but Group Y did. Following success the probability of a nonresponse in Group Y was 0.038, following failure 0.167 (U = 9, p < 0.01, MannWhitney U). So Group Y was more prone to give up after failure than after success. As in Experiment I, perseveration and position habits were examined according to the method of Krechevsky (1932). The criterion of going to the same side on at least 90 per cent of the trials for a day was used. Five animals in the escape group, four in the yoked group and four in the control group met this criterion for at least one day. The number of days in which these animals continued their position habits differed signi~cantly [F (2, 10) = 4.92, p < 0.05]. Newman-Keuls post hoc analyses revealed that the yoked animals (mean = 4.25 days) showed position habits significantly longer than either the escape (mean = 1.4 days) or control (mean = 1.75 days) animals (p’s < 0.05); the difference between the escape and control animals was not significant. No differences in food and water intake or body weight during development were observed among the groups. DISCUSSION
Interference produced by inescapable shock was retained from weaning to adulthood and was general from shock to appetitive discrimination learning, In both experiments the groups given inescapable shock as weanlings learned the discrimination tasks more slowly as adults than groups given equat amounts of escapable shock or no shock as weanlings. These data supplement the growing body of evidence on the generality and durability of the consequences of uncontrollability. Four explanations of the effects of inescapable shock have been proposed: learned helplessness, learned inactivity (Glazer and Weiss, 1976), competing motor responses (Bracewell and Black, 1974) and norepinephrine depletion (Miller and Weiss, 1969). Norepinephrine depletion, a transient phenomenon, cannot explain the long retention. Learned inactivity and competing motor response hypotheses are both compatible with the data we report above. On other grounds (e.g. Maier and Seligman, 1976) we prefer the learned helplessness explanation, and feel it has been adequately supported against the alternatives. In addition, recent data showing deficits in rat discrimination learning produced by random outcomes eliminate competing motor responses as a factor (Mullins and Winefield, 1977; Winefield, 1977). The experiments reported here do not attempt to test among the different explanations of the consequences of inescapable shock. Rather they are an empirical demonstration of the robustness and generality of such consequences. The deficits we report are reminiscent of Maier’s (1949) abnormal fixation results. Maier showed a reduction in a rat’s ability to learn a solvable discrimination following experience with unsolvable discrimination problems in a Lashley Jumping Stand. Rats typically showed a ‘fixated’ or consistent response to one side only. Are learned heipiessness and abnormal fixations the same phenomenon? Here are the similarities: (a) operationally both result in deficits in performing discrimination learning in a Lashley Jumping Stand; (b) operationally, both are induced by uncontrollability. In Maier’s case uncontrollability is induced by exposure to food, with the probability of food for a response to the left or to the vertical equal to the
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probability of food for a response to the right or the horizontal. In the learned helplessness case, uncontrollability is induced by exposure to shock with the probability of shock termination equal no matter what response is emitted; (c) both Maier’s rats and our rats given inescapable shock at weaning display response perseveration in a discrimination task; (d) both our rats and Maier’s rats show response initiation deficits. In fact, Maier’s rats were so reluctant to respond that special goading procedures (see below) were used to force response initiation. Here are the differences between Maier’s phenomenon and learned helplessness: we did not observe the extreme stereotypy and abortive jumping that Maier reported: this may result from the fact that Maier’s procedures involved more than mere appetitive uncontrollability. He also presented shock or airblast to goad his rats into responding. These aversive events were controllable since responding rather than not responding escaped them, At any rate, his inducing procedure confounds controllability and therefore differs from ours, which involves only uncontrollability. It should be noted, however, that Bainbridge (1973) reported ‘impairment at discrimination learning resulting from procedures similar to Maier’s but without aversive prods. Since failure to solve discrimination problems and perseveration tendencies can come about in several ways, our argument is only inferential; the fact that both Maier’s inducing procedure and inescapable shock are instances of response-outcome independence bolsters the inference. The appropriate test of whether uncontrollable shock and unsolvable discrimination problems produce the same phenomenon or, put even more strongly, that uncontrollability causes abnormal fixations would be to replicate Maier’s complex testing procedures, finding that both prior inescapable shock and unsolvable problems produce the abnormal fixations. Are the deficits shown in the discrimination learning task merely response initiation deficits or learning deficits? While there is clear evidence for response initiation deficits, there is no direct evidence for difficulty in learning what discriminanda were correlated with food once a response had been initiated. ‘Helpless’ rats were slower to respond, slower to reach criterion and made fewer correct responses. But all of these deficits are attributable to retarded response initiation, i.e. they made fewer responses overall. When equated for number of exposures to the discriminanda-reward contingency the groups did not differ in ease with which they learned the discrimination task. So the basic deficit appears to be one of response initiation rather than of learning. This is not equivalent to saying that learned helplessness results only in a performance deficit and not in a learning deficit. Failure to initiate responses on the discrimination task. failure to escape shock (Overmier and Seligman, 1967) as well as slower decreases in latency across trials in either task, could be caused by either lack of motivation (performance deficit) or by a retarded ability to associate responding with reinforcement (learning deficit). This experiment does not test between these interpretations: all this experiment shows is that there is no deficit in discriminanda-reward learning, but it does not preclude a deficit in response-reward learning. In conclusion, we suggest that weanling rats learn and retain into adulthood the expectancy that outcomes are independent of their responses. This learning undermines performance on a wide range of instrumental tasks. Rats who learn that shock termination is independent of responding show deficits at food-motivated discrimination learning and make fewer responses to obtain food. We suggest that both learned helplessness produced by inescapable shock and ‘abnormal fixations’ produced by uncontrollable food may be caused by learning that outcomes and responding are independent. REFERENCES ALTENOR A., KAY E. J. and RICHTER M. L. (in press) The generality of learned helplessness in the rat. Learn. Morir. BAINBRIWE P. L. (1973) Learning in the rat: effect of early experience with an unsolvable problem. J. romp. ph~iof. Psycho/. 82. 301-307. BRACEWELL R. 1. and BLACK A. H. (1974) The effects of restraint and non-contingent pie-shock on subsequent
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42, 207-208.
GLAZER H. 1. and WEISSJ. M. (1976) Long-term interference effect: an alternative to ‘learned helplessness’. 1. cup. Psycho/: Anirn. Proc. 2, 202-213. HANNUM R. D.. ROSELLIE;~ R. A. and SELIGMANM. E. P. (1976) Learned helplessness in the rat: retenuon and immunization. DL’v.Psychol. 12. 449-454. MAIER N. R. F. (1949) Frustration. University of Michigan. Ann Arbor. MAIERS. F.. ANDERSONC. and LIEBERMAN A. A. (1972) Influence of control of shock on subsequent shockelicited aggression. J. cornp. physiol. Psycho/. 81, 94-100. MAIER S. F. and SELIGMANM. E. P. (1976) Learned helplessness: theory and evidence. J. exp. Psycho/.: Gun. 105, 346. MILLER N. E. and WEISS J. M. (1969) Effects of somatic and visceral responses to punishment. In Punishment and Auersioe Behuuior (Edited by B. A. CAMPBELL and R. M. CHURCH),pp. 343-372. Appleton-Century-
Crofts. New York. OVI.RMIERJ. B. and SELIGMANM. E. P. (1967) Etfects of inescapable shock upon subsequent escape and avoidance learning J. cornp. physiol. Ps)lcho/. 63, 23-33. ROSELLINIR. A. and SELIGMANM. E. P. (1975) Frustrntion and learned helplessness. J. rxp. Psychof.: Auim. Beh. Proc. 104, 1949-1957.
ROSELLINIR. A. Exposure to noncontingent food interferes with the acquisition of response to escape shock. Unpublished manuscript. SELIGMAN M. E. P. (1975) Helplessness: On Depression. Deueloprnenr and Death. W. H. Freeman. San Francisco. WEINSKICKR. B. (1972) Maintenance schedules and hunger drive: an examination of the rat literature. Psycho/. Bull. 78, 31 I-320.
GARBER,?ELLEN FENCIL-MORSE,ROBERTA. ROSELLINI and MARTIN E. P. SELIGMAN Department of Psychology. University of Pennsylvania. 3815 Walnut Street. Phiiadelphi~ PA 19104, U.S.A. (Receiced 3 Junuars 1978)
Summary-Weanling rats received escapable, yoked inescapable. or no eiectric shock. Tested as aduhs. the inescapable groups were poor at appetitive discrimination teaming in either a parallel arm maze (Experiment I) or a Lashley jumping stand (Experiment 2). They were slower to respond. slower to reach criterion. made fewer correct responses and more non-responses than the escapable or no shock groups. We suggest that rats retain learned helplessness from weaning to adulthood. that such learning generalizes widely and that learned helplessness may explain the abnormal fixation results of Maier (1949).
This paper asks three questions: (a) is learning about uncontrollability retained from weaning to adulthood in the rat? (b) does this learning generalize from inescapable shock to appetitive di~imination learning? and (c) what is the relationship between the ‘abnormal fixations’ of Maier (1949) and ‘learned helplessness’ (Se&man. 1973 Adult dogs, rats and humans exposed to inescapable electric shock show marked deficits in later escape learning, whereas animals exposed to equal amounts of escapable shock show no such deficit. Learning deficits resulting from experience with inescapable shock and the hypothesized mediating process, learning that outcomes are independent of responding, have been dubbed ‘learned hetplessness’ (see Maier and Seligman, 1976; Seligman, 1975, for a review). Recently, Hannum et al. (1976) found shock escape deficits in adult rats even when inescapable shock was given 60 days previously, shortly after weaning. This paper reports deficits in adult appetitive discrimination learning resulting from inescapable shock received as a weanling. How general across different motivational states is interference produced by inescapable shock in the rat? Inescapable shock in adult rats interferes with learning to escape frustration produced by nonreward (Rosellini and Seligman, 1973, with learning a free operant bar press for food (Rosellini, unpublished manuscript), with learning underwater escape (Altenor et al, in press), and with shock-elicited aggression (Maier er al., 1972). So, interference produced by inescapable shock appears quite general to other tasks in adult rats. The present experiments extend the generality to complex discrimination learning for food and show that the deficit can be produced even when the original learning takes place early in life. We found that inescapable shock impaired discrimination learning, and the observed deficits were reminiscent of Maier’s (1949) ‘abnormal fixation’ data. Learned helplessness has been posed as a model of depression; it has also been suggested that helplessness may underlie other forms of maladaptive behavior, such as abnormal fixations, as well (Seligman, 1975). We suggest below that learned helplessness may be the basis of the phenomenon observed by Maier. * This study was supported by National Institute of Mental Health Grant (MH 19604) and a Guggenheim Fellowship to M. E. P. Seligman and National Institute of Mental Health Postdoctoral Fellowship (MH 00980-02)Vto R. A. Roseflini. Request for reprints should be sent to M. E. P. Seiigman, Department of Psychology, University of Pennsylvania, 3815 Walnut Street, Philadelphia, PA 19104, U.S.A. t Now at Psychology Dept.. University of Minnesota, 7.5 East River Road. Minneapolis, MN 55455,U.S.A. 197
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Method Subjects. The subjects were 24male Holtzman rats, 25 days old and weighing 64-77 g on the first day of pretraining. They were singly housed, maintained on a6 lib. food and water, and were run during the light phase of the 12 h dark/l2 h light cycle. Apparatus. Shock training. Shock was administered in jump-up boxes 23.5 cm long, 20.0 cm wide and 20.0 cm high. The end walls were constructed of stainless steei, the side walls and roof of clear Plexiglass. The floor consisted of stainless steel grids 0.4 cm in diameter, spaced 1.5 cm apart. The box was illuminated by a 75 W bulb mounted 13.0cm above the floor in the center of the end wall opposite the platform. Shock of l.OmA intensity was delivered to the animal by a constant-current shock source consisting of a 600 V (A.C.) transformer and a limiting resistor. An electrode lead entered through the ceiling of the chamber and was attached to a safety-pin electrode mounted subcutaneously in the animal’s upper back. The shock circuit was completed through the grid floor. Shock pulsated at a rate of 5 cps, with an equal on/off cycle. A trial began with the delivery of shock and with the upper ll.Ocm of the platform end-wall sliding back to expose the 20.0 cm wide and 12.5 cm deep platform. The platform was electrified on each trial for the inescapable group and was nonelectrified for the escapable group. When the animal jumped on to the platform, shock terminated for animals in the escape group and. for their yoked inescapable partners. If the animal failed to escape, shock remained on for 6Osec. White masking noise was present during the experimental sessions. Discrimination learning. A parallel arm maze was used for discrimination testing when the rats reached 100 days of age. The maze consisted of a 13.Ocm long start box, a 26.0 cm long runway to the choice-point area, and two 35.Ocm goal boxes placed parallel to one another with the sides touching; the choice-point area between the runway and the goal boxes was 26.Ocm long and 8.0 cm wide. The walls of the maze were constructed of unpainted plywood and the floor consisted of moisture-resistant disposable brown paper over a plywood base. The maze was covered by a clear Plexiglass lid and illuminated by two 75 W bulbs mounted in the ceiling of the room, each bulb 165.Ocrn from the maze, one 35.0 cm in front of the start box and the other 35.0cm behind the ends of the goal boxes. A timer was activated as the guillotine startbox door was raised. Photocells located 4.0 cm in front of the startbox and 4.5 cm from the ends of each of the goal boxes measured start and goal latencies. A 4.0cm long, 2.5 cm wide and l.Ocrn high food cup was mounted on the endwall of each goal box and rested on the floor. Plexiglass guillotine doors separated the runway from the start box and the choice-point area from the goal boxes. Black and white stimulus cards covered the entire wall surface inside the goal boxes; one card had a 3.Ocm wide horizontal stripe pattern, the other, a 3.0 cm wide vertical stripe pattern. The stimulus patterns were visible from the choice point. Food was consistently correlated with one stimulus pattern and absence of food with the other (counterbalanced). ~xperi~e~tu~ design. Three groups were used, one experimental and two control. Beginning with jump-training at 25 days of age, the experimental group received inescapable shock (Group Y, N = 8) yoked for the same pattern and duration to an escapable shock control group (Group E, N = 8). The other control group was not shocked (Group 0, N = 8). Four shock sessions were given, one every third day until the rats were 34 days old. At 100 days of age, all animals received discrimination testing in the parallel arm maze. Correct responses were rewarded with ten 45 mg Noyes food pellets; incorrect responses were not rewarded. Procedure Shock training. Jump-up shock escape training began at 25 days of age. The shock training procedure was similar to that employed by Hannum et al. (1976). Prior to the first training session each animal’s back was shaved from the neck to the tail to
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prevent the attenuation of shock by rolling on its back, and each subject was weighed. Escape training consisted of exposing the animals in Group E to 60 trials of l.OmA shock, which could be escaped by jumping up on the platform. Shock onset and the availability of the platform were simultaneous. This procedure resulted in consistent escape in all Group E animals by the end of training. Each animal in Group Y was yoked to animal in Group E so that each pair received identical durations and patterns of shock. Shock was therefore inescapable for the Group__Y animals, since its termination was controlled by the animals in the escapable group. Shock was given on a variable interval 1-min schedule with a range of 15-105 set; the shock session was approximately 60 min long. Animals in Group 0 (nonshocked controls) were also shaved, implanted with a subcutaneous safety pin electrode and placed in operant chambers for the same amount of time, but were not exposed to shock. Discrimination learning. Following shock training, all animals were maintained on ab lib. food and water for the next 64-66 days. During this period animals were not handled. At 100-102 days of age animals were placed in the parallel arm maze and habituation training began. On trial one of the first day of habituation, each animal was placed in the start box of the runway with the guillotine to each of the goal boxes raised; the start box door was then raised and the animal was allowed to explore the maze for 3 min. On the next two habituation trials of the first day, the animals were placed in the right-hand goal box for one trial and in the left-hand goal box for the other trials; all guillotine doors were raised. The fourth trial was a repetition of the first trial. Each animal received four trials per day on four different days. On day three of habituation, total food deprivation began until the animals reached 85% of their free-feeding body weight. They were then maintained on 850/, fixed body weight deprivation schedule (Weinstock, 1972). The range of initial body weights for the three groups was 31 l-394 g. The order of box placement changed systematically as follows: day l/start box (S), right goal box (R), left goal box (L), start box (S); day Z/RLSR; day 3/LSRL; day 4/SRLS. Habituation days were nonconsecutive, two days of rest intervening between habituation days 2 and 3, and three days between 3 and 4. During habituation, stimulus cards were randomly switched from the right to the left goal box and vice versa. On day 1 of maze training each animal was given ten 45 mg Noyes food pellets prior to trial 1 in the home cage. During the 15 consecutive days of maze training each animal received 10 trials per day. On each trial the animal was placed in the start box, facing the goal, and the guillotine door to the start box was raised. After the animal entered the goal box the guillotine door was lowered to prevent retracing. The horizontally striped goal box choice was reinforced for half the animals; the vertically striped goal box choice was reinforced for the other half. Reinforcement consisted of ten 45 mg Noyes pellets in the goal box food cup. On incorrect trials the animal waited in the foodless goal box for 30 set before being replaced in its home cage. Animals were always run in the following order: El, Y,, C,, El, Y,, C1, E3.. . . The intertrial interval was approximately 30 min. RESULTS Shock
AND
DISCUSSION
training
All animals in Group E learned the escape response. No failures to escape were observed in this group during the last 20 training trials. The mean amount of shock received by Groups E and Y was 668.44sec with a standard error of 649.70sec. Discrimination
learning
The inescapable group did poorly at discrimination learning whereas the escape and nonshocked groups did well. Maze performance showed the typical acquisition curves of increasing percent correct per day over the first 13 days of training with asymptotic performance on days 13-15 for Groups E, Y and 0. Figure 1 presents the per cent
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Fig. I. Mean
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correct over days for the three groups. A 3 x 15 repeated measures analysis of variance showed significant differences among the three groups throughout training, F (2,21) = 4.43. p < 0.025; a significant effect of days TF (14,294) = 31.8, p < O.OOl]; and no significant groups x days interaction, F < 1. Newman-Keuls posr hoc tests showed both Groups E and 0 to have higher per -ctmt correct than Group Y (p’s < 0.05). Groups E and 0 did not differ significantly in percent responses correct across days. Similarly, the groups differed significantly on the number of trials to reach the SO”/:, correct criterion (80% correct responses during a single day of discrimination trials) [F (2, 21) = 7.125, p--c 0.011. Newman-Keuls post hoc tests showed that Group E (mean = 59.57) took fewer trials to reach criterion than Group Y (mean = 107.0) @ < 0.05). Group 0 (mean = 78.0) did not significantly differ from either Group E or Group Y. Did the yoked animals develop more persistent position habits than the escape or control animals? Systematic response tendencies (hypotheses) were examined using a method suggested by Krechevsky (1932) and Levine (1975). For each rat the following items were determined: (1) number of ‘errors’ the animal made each day; (2) the number of jumps to the left; (3) the number of juinps to the right: and (4) the number of jumps in keeping with an ‘alternating’ scheme.* The groups differed si~i~cantly for the total number of days on which ‘systematic’ behavior was observed [F (2,19) = 8.57, p -C 0.011. Newman-Keuis post hoc analyses revealed that animals in the yoked group (mean = 6.28 days) responded in a systematic manner (universally position habits) significantly longer than both the escape (mean = 2.57 days) and the control (mean = 3.0 days) animals (p < 0.05). Four animals (three from Group Y and one from Group 0) maintained a position habit over the entire course of the experiment and thus failed to reach the 80% correct criterion of correct responses. The remaining animals typically showed a brief period of random sampling prior to attaining the criterion. Thus it may be that this transition from position habit to the appropriate discriminated response is delayed or prevented by exposure to inescapable shock, resulting in the observed Group Y deficit in correct responding. This deficit, particularly the failure to give up a position preference, is reminiscent of Maier’s (1949) abnormal fixation results and those of Bainbridge (1973). Maier found that rats exposed to unsoivable discrimination problems in a Lashley jumping stand subsequently failed to learn when the problems were made solvable. They typically showed ‘fixated’ behavior, responding consistently to one side only. Would inescapable
* From these data a series of ‘learning’ curves were plotted for each rat. To determme if the appearance of systematic responses. e.g. position preference, was a chance fluctuation, following Krechevsky (1932). we used the criterion of k2.5 SD. from chance [where SD. = ,/(PQ/N)]. For this study, this meant that responding to one side on at least 90 per cent of the trials constituted a significant position bias.
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shock given to weanling rats produce similar deficits at adult discrimination learning on a Lashley jumping stand? Experiment 2 attempts to replicate and extend the results of Experiment 1 to a different kind of apparatus. Three groups of weanling rats received escapable, inescapable, learning task on the Lashley or no shock and were tested on an appetitive discrimination jumping stand. EXPERIMENT
2
Method Subjects. The subjects used were 24 male Sprague-Dawley rats, received from the Holtzman Company when they were between 22 and 24 days of age. They were singly housed. maintained on ab lib. food and water, and were run during their light phase of the 12 hr dark/l2 hr light cycle. Apparatus. The same pretraining apparatus described in Experiment 1 was used. Discrimination testing. The appetitive discrimination apparatus was a modified Lashley Jumping Stand. It consisted of three-ply pine, 91.44 cm wide and 152.4 cm high, having two 14cm square holes cut 76.2 cm from the floor and spaced 5 cm apart. Attached to the back of the screen, 0.64 cm below the lower edges of the openings was a 30.5 cm platform on which food was placed. A starting platform, 25 cm in diameter, from which the animal jumped was placed in front of the middle of the screen. The distance between the stand and the screen varied systematically and is outlined in the procedure. A projecting sheet of metal served to deflect the rat through the openings in case he jumped too high. A 5 cm thick piece of foam rubber 45 cm wide and 91.44 cm long was placed below subjects in case of a fall. The openings were fronted with 15.2 cm squares of heavy cardboard upon which the horizontal and vertical discrimination patterns were drawn. One card bearing the negative stimulus was fixed rigidly by a metal door; the other card was left unfastened to allow the animal to jump against it and project his way through to the platform. Experimental design. Groups of eight triads were given training with either escapable, inescapable, or no shock shortly after weaning, and tested on an appetitive discrimination learning task as adults. A triad consisted of one rat receiving escapable shock (Group E), a yoked rat receiving the same pattern and duration of shock as his partner (Group Y), and a third rat receiving no shock (Group 0). The animals were randomly assigned to the three training conditions. Procedure Shock training. The shock training procedure was the same as that outlined in Experiment 1. Appetitioe discrimination tesr. At 110-112 days of age all animals were placed and then maintained on an 85% fixed body weight deprivation schedule (Weinstock, 1972) for the duration of the experiment. The range of body weights for the three groups was 330-343 g. Preliminary discrimination training. Before beginning testing on the appetitive discrimination apparatus all animals were given three training days of 10 forced trials-five trials to each side according to a Gellerman (1933) order. On each trial the subject was required to go through one of the windows to the platform where they received five pellets of food (45 mg Noyes food pellets). The first day of training consisted of 3 min of exploration of the apparatus and exposure to the food. The jumping stand was adjacent to the open windows of the apparatus so the animal could walk across to the feeding platform. On the following two days they were given training in jumping from the stand through the open window in the screen to the feeding platform. This was done by retracting the stand back approximately 2.5 cm per trial from a position adjacent to the screen to a position 22.9 cm from the screen. On day 3, animals were trained to jump at and knock over the stimulus cards. One card had horizontal black
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and white lines (2.0cm wide). Cards were alternated from side to side according to a selected Gellerman order. The cards readily fell over whenever struck by the rat. To prevent the animal from jumping CotisistentIy to one side or one of the cards. manual guidance was introduced whenever the animal began to express a preference for one side or one card. This guidance consisted of pushing the rat away from the preferred window or card as soon as it prepared to jump. Discriminariun training. Beginning on the fourth day all animals were exposed to the visual discrimination problem in which the vertical card and the horizontal card were alternated from side to side according to the selected orders. Vertical was consistently locked for one-half of the animals in each group while horizontal was consistently locked for the other half. Responses to the unlocked stimulus were correct and were followed by five food pellets. Responses to the locked stimulus were incorrect and resulted in the animals falling to the foam rubber below. A ‘nonresponse’ was defined as the animal’s failure to jump within 180sec of being placed on the stand. Subjects received a total of 10 trials a day for 15 days. On each trial the animal was placed on the jumping stand, which was set at 12.7 cm from the screen for all test trials, until he responded or 180sec had elapsed, without a response. Correct, incorrect and nonresponses were recorded as well as latency to respond for each trial. Using a stopwatch, the experimenter recorded the latencies to the nearest tenth of a second. RESULTS
Shock
training
All animals in the escape group learned to jump onto the platform to terminate shock. No failures to escape were observed for any of these animals on the last 20 trials of training. The mean total amount of shock received by the escape group, and therefore the yoked group as well, was 994.65 set with a standard error of 702.46. Discrimination
test.
Animals receiving inescapable shock shortly after weaning were significantly slower to learn the discrimination as adults than either the escapable or nonshock group. Animals exposed to inescapable shock made substantially fewer mean correct responses per day (Group Y, mean = 7.47) across ‘the 15 days of discrimination learning than rats given either escapable (Group 3, mean = 8.99) or no shock (Group 0, mean = 8.92). A groups (3) x days (15) analysis of variance showed a significant effect for groups [F (2,211 = 5.45, p -z 0.05-J; a significant effect for days [F (14,294) = 36.14, p < 0.001 J; but no significant groups x days interaction, indicating that each group increased nondifferentially in the number of correct responses over days, and that differences existed in the number correct for the three groups. Newman-Keuls post hoc tests showed that Group Y made significantly fewer correct responses than either Group E or Group 0 (p’s < 0.05) which did not differ from each other. The differences in total number of correct responses is infiated by the fact that subjects in the inescapable group made significantly fewer jumps than either the escapable or nonshock groups. The 3 x 15 analysis of variance on number of jumps showed both main effects [F groups (2,21) = 10.5, p < 0.011 and [F days (14,294) = 7.18, p < 0.01) and the groups x days interaction [F (28,294) = 4.97, p < 0.011 to be significant. Newman-Keuls post hoc tests showed Group Y to have made significantly fewer jumps than either Group E or 0 Q’s < 0.01) which did not differ from each other. Figure 2 shows that Group Y initially made fewer jumps, while Group E and 0 jumped on almost every trial from the beginning of testing. Since the difference among the groups on the total number of correct responses is inflated by the fact that the inescapable group emitted significantly fewer responses, the per cent correct of only those jumps made was examined. This analysis attempts to determine whether any deficit over and above the failure to respond exists. Although Group Y (mean = 79.89%) made fewer per cent correct responses per day than Group E
‘Abnormal
Fig. 2. Mean
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and ‘learned
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of jumps for the Escape (E). Yoked (Y) and Control of ten trials per day. Experiment 2.
(0)
groups in blocks
(mean = 90.07%) or Group 0 (mean = 89.74%) this difference showed only a trend toward significance fF (2,21) = 3.15, p < 0.10-j. Newman-Keuls post hoc analyses showed Group Y to have made fewer per cent correct responses for actual resijonses attempted than Group 0 (p c 0.05); Group Y and Group E were not significantly different on this measure (p < 0.10). Figure 3 illustrates that Group Y decreased in mean latency over the 15 days of testing at a slower rate than either of the other groups. The mean latencies for actual jumps made reflected a similar pattern. Animals receiving inescapable shock were signi~cantly slower to respond than either the escapable or no-shock groups [F (2.21) = 6.38, p c 0.011. There was also a significant effect for days [F (14,294) = 22.57. p < 0.011. Newman-Keuls post hoc tests showed Group Y to have significantly longer response latencies than either Group E (p < 0.01) or Group 0 (p < 0.05). These groups did not differ from each other. These last two analyses, however, are not sufficient to establish that any learning deficit is present over and above the motivational deficit in response initiation, The inescapable group. since it made fewer responses per day, had less exposure to the discriminanda-reward contingency. Thus analysis by days rather than by blocks of trials on which responding occurred fails to equate exposure to the learning contingency. We therefore performed two 3 (groups) x 11 (blocks of 10 responses with nonresponses omitted) repeated measures analyses of variance on number correct and latency. These analyses showed that although the yoked group seemed to make fewer correct responses
Fig
3. Mean
latency
in seconds for the Escape (E), Yoked (Y) and Controt blocks of ten trials per day, Experiment 2.
(0)
groups in
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per blocks of ten jumps attempted than the escape or no-shock groups, this difference was not significant [F (221) = 1.57. n.s.1. The yoked group (Group Y, mean = 31.04) was signi~cantly slower to respond, however, than either the escape (Group E. mean = 15.05) or no-shock groups [F (2.21) = 4.20, p < O.OS]. Newman-Keuls post hoc tests showed Group Y to have significantly longer response latencies than either Group E or Group 0 @ < 0.01). These groups did not differ from each other. Thus a deficit in response initiation on the appetitive discrimination learning task appeared in the inescapable group but no deficit appeared in learning the discrimination once we equated for exposure to the contingency. Is the response initiation deficit greater after failure (incorect responses) than success (correct responses)? Groups E and 0 did not differ significantly in number of nonresponses following success vs failure, but Group Y did. Following success the probability of a nonresponse in Group Y was 0.038, following failure 0.167 (U = 9, p < 0.01, MannWhitney U). So Group Y was more prone to give up after failure than after success. As in Experiment I, perseveration and position habits were examined according to the method of Krechevsky (1932). The criterion of going to the same side on at least 90 per cent of the trials for a day was used. Five animals in the escape group, four in the yoked group and four in the control group met this criterion for at least one day. The number of days in which these animals continued their position habits differed signi~cantly [F (2, 10) = 4.92, p < 0.05]. Newman-Keuls post hoc analyses revealed that the yoked animals (mean = 4.25 days) showed position habits significantly longer than either the escape (mean = 1.4 days) or control (mean = 1.75 days) animals (p’s < 0.05); the difference between the escape and control animals was not significant. No differences in food and water intake or body weight during development were observed among the groups. DISCUSSION
Interference produced by inescapable shock was retained from weaning to adulthood and was general from shock to appetitive discrimination learning, In both experiments the groups given inescapable shock as weanlings learned the discrimination tasks more slowly as adults than groups given equat amounts of escapable shock or no shock as weanlings. These data supplement the growing body of evidence on the generality and durability of the consequences of uncontrollability. Four explanations of the effects of inescapable shock have been proposed: learned helplessness, learned inactivity (Glazer and Weiss, 1976), competing motor responses (Bracewell and Black, 1974) and norepinephrine depletion (Miller and Weiss, 1969). Norepinephrine depletion, a transient phenomenon, cannot explain the long retention. Learned inactivity and competing motor response hypotheses are both compatible with the data we report above. On other grounds (e.g. Maier and Seligman, 1976) we prefer the learned helplessness explanation, and feel it has been adequately supported against the alternatives. In addition, recent data showing deficits in rat discrimination learning produced by random outcomes eliminate competing motor responses as a factor (Mullins and Winefield, 1977; Winefield, 1977). The experiments reported here do not attempt to test among the different explanations of the consequences of inescapable shock. Rather they are an empirical demonstration of the robustness and generality of such consequences. The deficits we report are reminiscent of Maier’s (1949) abnormal fixation results. Maier showed a reduction in a rat’s ability to learn a solvable discrimination following experience with unsolvable discrimination problems in a Lashley Jumping Stand. Rats typically showed a ‘fixated’ or consistent response to one side only. Are learned heipiessness and abnormal fixations the same phenomenon? Here are the similarities: (a) operationally both result in deficits in performing discrimination learning in a Lashley Jumping Stand; (b) operationally, both are induced by uncontrollability. In Maier’s case uncontrollability is induced by exposure to food, with the probability of food for a response to the left or to the vertical equal to the
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probability of food for a response to the right or the horizontal. In the learned helplessness case, uncontrollability is induced by exposure to shock with the probability of shock termination equal no matter what response is emitted; (c) both Maier’s rats and our rats given inescapable shock at weaning display response perseveration in a discrimination task; (d) both our rats and Maier’s rats show response initiation deficits. In fact, Maier’s rats were so reluctant to respond that special goading procedures (see below) were used to force response initiation. Here are the differences between Maier’s phenomenon and learned helplessness: we did not observe the extreme stereotypy and abortive jumping that Maier reported: this may result from the fact that Maier’s procedures involved more than mere appetitive uncontrollability. He also presented shock or airblast to goad his rats into responding. These aversive events were controllable since responding rather than not responding escaped them, At any rate, his inducing procedure confounds controllability and therefore differs from ours, which involves only uncontrollability. It should be noted, however, that Bainbridge (1973) reported ‘impairment at discrimination learning resulting from procedures similar to Maier’s but without aversive prods. Since failure to solve discrimination problems and perseveration tendencies can come about in several ways, our argument is only inferential; the fact that both Maier’s inducing procedure and inescapable shock are instances of response-outcome independence bolsters the inference. The appropriate test of whether uncontrollable shock and unsolvable discrimination problems produce the same phenomenon or, put even more strongly, that uncontrollability causes abnormal fixations would be to replicate Maier’s complex testing procedures, finding that both prior inescapable shock and unsolvable problems produce the abnormal fixations. Are the deficits shown in the discrimination learning task merely response initiation deficits or learning deficits? While there is clear evidence for response initiation deficits, there is no direct evidence for difficulty in learning what discriminanda were correlated with food once a response had been initiated. ‘Helpless’ rats were slower to respond, slower to reach criterion and made fewer correct responses. But all of these deficits are attributable to retarded response initiation, i.e. they made fewer responses overall. When equated for number of exposures to the discriminanda-reward contingency the groups did not differ in ease with which they learned the discrimination task. So the basic deficit appears to be one of response initiation rather than of learning. This is not equivalent to saying that learned helplessness results only in a performance deficit and not in a learning deficit. Failure to initiate responses on the discrimination task. failure to escape shock (Overmier and Seligman, 1967) as well as slower decreases in latency across trials in either task, could be caused by either lack of motivation (performance deficit) or by a retarded ability to associate responding with reinforcement (learning deficit). This experiment does not test between these interpretations: all this experiment shows is that there is no deficit in discriminanda-reward learning, but it does not preclude a deficit in response-reward learning. In conclusion, we suggest that weanling rats learn and retain into adulthood the expectancy that outcomes are independent of their responses. This learning undermines performance on a wide range of instrumental tasks. Rats who learn that shock termination is independent of responding show deficits at food-motivated discrimination learning and make fewer responses to obtain food. We suggest that both learned helplessness produced by inescapable shock and ‘abnormal fixations’ produced by uncontrollable food may be caused by learning that outcomes and responding are independent. REFERENCES ALTENOR A., KAY E. J. and RICHTER M. L. (in press) The generality of learned helplessness in the rat. Learn. Morir. BAINBRIWE P. L. (1973) Learning in the rat: effect of early experience with an unsolvable problem. J. romp. ph~iof. Psycho/. 82. 301-307. BRACEWELL R. 1. and BLACK A. H. (1974) The effects of restraint and non-contingent pie-shock on subsequent
learning
in the rat. Learn.
Motiv. 4, 5369.
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206 GELLERMANL.
Psyhol.
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