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An interaction between appetitive Pavlovian CSs and instrumental avoidance responding
LEARNING
AND
(1970) 1, 18-26
MOTIVATION
An Interaction
Between
Instrumental
Appetitive Avoidance
JOHN
A.
University
BULL,
Pavlovian Responding
CSs and ’
III2
of Minnesota
Three groups of dogs were first trained to avoid shock by responding during a visual signal. Second, these groups underwent appetitive Pavlovian conditioning operations in a different environment. Later when compounded with the cue for avoidance in transfer tests, a CS+ which had reliably signaled food presentations during Pavlovian conditioning produced marked decreases in rates of avoidance responding, while a CS” which had been presented randomly with respect to food, and a CS- which had been contrasted with food, produced no effect. This class of Pavlovian conditioning + instrumental responding interaction experiments has been the subject of theoretical controversy. These results suggest that appetitive and aversive conditioned motivational states interact subtractively.
Recent experiments have shown that Pavlovian CSs can influence and/or control instrumental responding (Trapold & Winokur, 1967; Bull & Overmier, 1968). Such experiments typically present an appetitive Pavlovian CS in an instrumental appetitive situation or present an aversive Pavlovian CS in an instrumental avoidance situation, the Pavlovian stimuli having been established by separate operations independent of the instrumental training. The rationale for this general experimental paradigm is derived from two-process theories of instrumental learning (cf., Rescorla & Solomon, 1967) in which states established by Pavlovian conditioning are thought to be important in the control and modulation of instrumental responding. Rescorla and Solomon (1967) point out the utility of such experiments in providing basic data from which a more comprehensive behavior theory may be derived, and ‘This research was supported by U. S. Public Health Service Grant MH-13558 to J. Bruce Overmier who directed the Ph.D. dissertation submitted to the University of Minnesota upon which this article is based. The author also thanks Milton A. Trapold for his comments on an earlier draft of this paper. 2 During the course of this investigation, the author was a National Institute of Mental Health Predoctoral Fellow No. I-Fl-MH-35, 727-Ol-PS. Requests for reprints should be sent to the author, Department of Psychology, The George Washington University, Washington, D. C. 20006. 18
PAVLOVIAN-INSTRUMENTAL
INTERACTION
19
they further point out that in order to develop more explicit theoretical mechanisms, data regarding the interaction between appetitive CSs and instrumental avoidance behavior would be of crucial interest. Two recent experiments have provided suggestive evidence with regard to this interaction. Coulson and Walsh (1968), using a design that was the inverse of the typical conditioned suppression experiment, superimposed a CS followed by food on an unsignaled baseline of instrumental avoidance responding in rats. They found that the CS produced a slight increase in the rate of bar press avoidance responding. These results were interpreted as being inconsistent with a general energizing or motivational effect conditioned to the CS. A second experiment has recently been described by Grossen, Kostansek, and Bolles (1969). Here, rats were first given training in a two-way shuttle box to avoid a periodic, unsignaled shock. They were then given Pavlovian conditioning trails in which, for different groups: (a) the CS was paired with food (CS+); (b) the CS signaled a period when no food would be delivered (CS-); and (c) the CS and food were presented randomly with respect to each other in time (control CSO). These groups were then tested by superimposing the CS on the instrumental avoidance response baseline. It was found that the response rate to the CS+ was lower and response rate to CS- higher than the response rate to the control CSO. Thus the appetitive CS+ depressed avoidance responding, while the CS- enhanced it. This is consistent with the view that appetitive CS+‘s somehow decrease the aversiveness of the stimuli controlling avoidance responding while the appetitive CS-‘s are themselves aversive and add to the aversiveness state controlling avoidance responding. These two experiments indicate that the scant evidence regarding appetitive + aversive interaction is inconsistent and inconclusive. In order to provide additional data, the present experiment used appetitive Pavlovian conditioning procedures to establish CS+, CS-, and CS” signals and then tested the effects of these CSs when presented in combination with a separately established SD for avoidance responding. METHOD
Subjects The Ss were 15 mongrel dogs, 15-19 in. high at the shoulder. They were obtained from the University of Minnesota animal hospital, and housed in individual cages. Ss were food deprived and maintained at approximately 80% body weight. Water was continuously available. Each S was arbitrarily assigned to one of three groups.
20
JOHN
A.
BULL,
III
Apparatus
The avoidance training apparatus was a two-way shuttlebox with two compartments separated by an l&in. barrier and a removable dropping door which isolated the two compartments. Each compartment was 45 X 24 in. and 40 in. high, with plywood walls painted flat black. Ceilings were made of hardware cloth. Above each compartment ceiling, a lo-in. high, enclosed chamber contained a 7.5 W light, a 150 W light, and two 5 X 7 double cone speakers. A one-way mirror was mounted in the front of each chamber to permit observation of the Ss. One speaker in each chamber continuously introduced approximately 70 db (re: .0002 dynes/ sq cm) of white noise into each compartment. The remaining speaker was used to present the tone CSs approximately 15 db above the continuously present white noise level. Electric shock was administered through a grid floor of la in. aluminum bars placed g in. apart. A commutator shifted the polarity patterns of the bars six times per second. The shock source consisted of a 600-V transformer to which a variable input from an autotransformer connected to 110 Vat could be applied. A current limiting resistence of 50,000 ohms was placed in series with the S and the current was continuously monitored with a meter. Trial duration was measured to the nearest .Ol set, using a standard electric timer controlled by two photocell relays placed in each compartment, 14 in. from the grid floor and 11 in. from each side of the barrier. Responses during trials as well as responses between trials were recorded using both a cumulative and an event recorder. Stimulus presentations and temporal contingencies were controlled by automatic relay circuitry, housed in an adjacent room. Pavlovian conditioning took place in a separate, partially soundproof, 5 X SQ-ft booth, 6$ ft high. The dogs were supported 30 in. above ground level by a 34 X 17-in. plywood floor in a metal frame made of l&in. pipe. This frame also supported an aluminum tray, 14 in. above the plywood floor to which was fastened a food cup. A specially designed and constructed rotary pellet dispenser was located above and to the left of the dog’s head, approximately 22 in. from the food cup. The food dispenser operated with an audible click dropping a pellet into a chute which carried the pellet to the food cup. Part of the metal frame encircled the dog about chest high, discouraging escape. The dogs were further restrained by a collar, fastened to the ceiling of the booth and to each side of the frame by a light chain, but loosely enough so that the food could easily be reached and the animals would not be unduly upset. Two 6 X 9-in. speakers introduced continuous white noise into the booth at approximately 80 db. A third 6 X 9-in. speaker introduced the tone CSs at about 15 db above the white noise level. All speakers were
PAVLOVIAN-INSTRUMENTAL
INTERACTION
21
located along the top of the back wall. The booth was illuminated by four, 12-V lamps, one located above, and three above and in front of the animals. Automatic relay circuitry, controlling stimulus presentations and temporal contingencies, was located outside the booth. Treatments Training sessions took place on consecutive days. Ss were placed in the apparatus approximately 5 min before the start of each session and removed approximately 5 min after each session and placed in their home cages. All Ss were maintained on food deprivation starting approximately 7 days before the first training session. Znstrumerztal avoidance training. In the first stage of the experiment, all Ss were trained to avoid shock by jumping the barrier in the shuttlebox. Each session consisted of 21 trials and each trial was initiated by the onset of a visual SD (switching off both 150-W lamps). If the S did not cross the barrier within 10 set (CS-UCS interval), the UCS (4.5 mA shock) was turned on and remained on until S crossed the barrier or until 50 set had elapsed and the trial terminated. Crossing the barrier terminated both the SD and UCS. A response by S within 10 set of the SD onset, terminated the trial and avoided the shock. The average intertrial interval was 120 set and ranged between 45 and 180 sec. This training was continued until a criterion (no shock) during a daily session was met. The CS-UCS interval was then shortened to 5 set and the S was again required to meet the criterion of no shocks during a session. When this criterion was met, each S was given a special second stage of instrumental avoidance training designed to build up the rate of barrier crossing through what amounts to a discrete trial variable interval schedule of reinforcement. This second stage was characterized by a variable interval (VI) hold period during which the CS was on but responses did not terminate the SD. This hold period varied and was either 0, 3, 6, 12, or 18 set long, but only three of these values were used during any one session, seven trials per session with each hold period used. At the end of the hold period, the next barrier jumping response terminated the SD. If no response was made within 5 set of the termination of the hold period, a 9-mA shock of 0.5 set duration was delivered. The schedule resulted in a stable rate of barrier jumping controlled by a discrete trial stimulus. The first sessions of this schedule involved the holds: 0, 3, and 6 sec. When a criterion of five or less shocks per daily session was met, the hold periods were changed to 0, 6, and 12 sec. When the criterion of five or less shocks was again met, the hold periods were changed to the final settings of 0, 6, and 18 sec. Training was continued until each S met a final criterion of no shocks for two consecutive daily sessions or
22
JOHN
A.
BULL,
III
until 10 days of VI-hold training had transpired, after which Pavlovian conditioning was begun. Pavlovian conditioning. In the second stage of the experiment, Ss received 21 appetitive conditioning trials per day over six consecutive daily sessions. A UCS presentation consisted of one food pellet dropped in front of the dog’s nose (Gaines: Prime pellets). Each S was placed in one of three groups. In the CS+ group, a 1200-cps tone was paired with food. In the CS- group, a 1200-cps tone was contrasted with food such that the tone signaled a period in which food would not be presented. In the CS” control group, a 1200-cps tone was presented randomly with respect to the 21 food presentations. The duration of the CS tones was either 5, 10, or 15 set, seven of each presented in random order during a session. When a CS was paired with food, the food was delivered at the termination of the CS. When a CS was contrasted with food, the food was delivered during an inter-trial interval such that a CS signaled no food for at least 40 sec. This interval varied with a maximum of 120 set and an average of 80 sec. In the random control group, the tone was programmed randomly with respect to the UCS but scheduled so that the inter-CS intervals and interUCS intervals were equal to the contingent groups in average duration and range. All groups were equated in session duration and reinforcement density, and received 21 UCS presentations per day. On the day following the last Pavlovian conditioning session, an added day of VI-avoidance training was given, exactly as before. On the day following this, testing was begun. Testing. The testing was carried out during extinction trials of the avoidance response in the shuttle box. Two types of test trials were given: (a) SD alone; and (6) 1200-cps tone and visual SD presented simultaneously (SD-plus-CS compound). Twenty-four test trials (12 of each type) were presented in random order during each of three daily sessions. Test trials for all groups were presented with an average inter-trial interval of 80 set and a range of 40 to 120 sec. Each trial used a IO-set hold period, during which responses were ineffective (as in training). The first response after the hold period terminated the trial and the test stimuli. If no response was made within 30 set after the end of the hold period, the trial and test stimuli were automatically terminated. RESULTS
Rate of barrier jumping each S on every test trial during each of the two every S. The group mean
during the IO-set hold period was recorded for and daily mean response rates (jumps/minute) test stimulus conditions were calculated for response rates under each test stimulus con-
PAVLOVIAN-INSTRUMENTAL
K a a
20
I
INTERACTION
cs+ cso
o......a
cs-
iYJ. .. . .. . .a
I
23
I
SD
sD+cs STIMULI
FIG. 1. Mean avoidance response rates (jumps/minute) condition.
for each group to each stimulus
dition are presented in Figure 1. An analysis of variance revealed a significant difference between Groups (F = 12.85, p < .Ol, df= 2/ 12) and a significant Group x Stimulus Condition interaction (F = 5.85, p < .05, df= 2/12). A comparison of means between the two test stimulus conditions within each group revealed that the decrease in response rate during the SD-plus-CS compound for the CS+ group was significant (t = 6.46, p < .Ol, u”= 12).3 The slight decrease in the CS” group was not significant while the similar decrease in the CS- group did just reach significance (t = 2.75, p < .05, df= 12). However, these decreases are confounded with any stimulus generalization decrement due to the novel presentation of the SD-plus-CS compound in the test situation [indeed, if the random control procedure provides a truly neutral CS (Rescorla, 1967), all of the decrease in the CS” group may be accounted for in this way]. Because the confounding factor may have been responsible for part of the decrease observed in the CS+ group and possibly account for all of the decrease observed in the CS” and CS- groups (which were behaviorly quite similar), means between groups were compared for the SD-plus-CS compound condition, a comparison which avoids such confounding. The large difference between the CS+ and CS” groups was significant (t= 5.51, p < .Ol, df= 12) as was the large difference between the CS+ and CS- groups (t = 5.02, p < .Ol, df= 12). The slight difference between the CS” and CS- groups was not significant. However, comparisons between group means for the baseline SD condition 3 All f tests are two tailed.
24
JOHN
A.
BULL,
III
uz. % rcs+ I 2 40
-
g 30
-
!-f 20 l2 a0 IO-
cso cs-
0 ......... 0 D.............fl
*......a g;&.:;;:;;.;~~&$:2’.yo I I
I 2
I 3
TEST DAYS 2. Means of daily percent decreases in avoidance response rates during the SDplus-CS compounds relative to the response rates during the SD alone (i.e., [SD rate - compound ratellS’ rate). FIG.
indicated that while differences between the CS+ and CS” groups as well as between the CS- and CS” groups were not significant, the difference between the CS+ and CS- groups did reach a low level of significance (t = 2.22, p < .05, df= 12). Although this slightly lower baseline rate for the CS+ group may have been due to across-trial generalization during testing of the large effect produced by the CS+ compound stimulus (an argument supported by the observation that the baseline differences increased over days), this baseline difference confounds the differences found in the SD-plus-CS condition. In order to take into account the possible confounding factors, daily percent rate decreases from baseline were calculated for each S. Group averages are presented in Figure 2. This measure compared the daily mean rate to the SD with the daily mean rate to the SD-plus-CS compound using the formula: [SD - (SD-plus-CS)]/SD. An analysis of variance indicated significant Group differences (F = 11.54, p < .Ol, df= 2/12). Between-group comparisons indicated that the percent decrease for the CS+ group was significantly greater than the CS” group (t = 4.32, p < .Ol, df= 12) or the CS- group (t = 3.98, p < .Ol, df= 12). The difference between the CS” and CS- groups was not significant. There was no significant effect of test days. DISCUSSION
A food-paired Pavlovian CS+ produced marked decreases in rate of avoidance responding when it was presented together with the SD controlling the avoidance behavior. Because similar decreases did not occur
PAVLOVIAN-INSTRUMENTAL
INTERACTION
25
to the randomly paired stimulus in the CS” control group, the results cannot be explained by stimulus generalization decrements, sensitization, or pseudoconditioning. These results strongly support the contention that a food-paired Pavlovian CS acquired mediational properties which are inherently incompatible with the mediational properties of a signal controlling avoidance responding. To the extent that the avoidance SD is also a mediational fear CS, a reduction in response rate during the presentation of a food-paired or hope CS is expected. This is consistent with Mowrer’s (1960) suggestion that CSs based on shock interact subtractively with CSs based on food and fails to support the contention that incentive functions are acquired by appetitive CSs which energize instrumental behavior regardless of the type of reinforcer involved (Coulson & Walsh, 1968). It should be noted that these experimental conditions are an inversion of the well documented conditioned suppression phenomenon (Estes & Skinner, 194 1) wherein a shock-paired CS is presented during appetitive responding. This response rate suppression produced by the shock-paired CS is also predicted by the notion of a subtractive interaction between conditioned anticipatory mediational states based on food and shock. Further, these results are consistent with those of Grossen et al. (1969) for the food-paired group. The failure of the CS- group to show an excitation effect, as did Grossen et al., is unexplained. This discrepancy could be due to species differences, procedural differences, or both. The parameters for the CS- group were selected so as to match the temporal and food density conditions of the CS+ group (as well as the CS” group), except for the CS-UCS pairing. Since little is known about optimal parameters for food contrast conditioning, it may be that the parameters used here were not sufficient for the development of any mediational state based upon absence of food. This would result in an ineffective CSwhich would act essentially the same as a randomly paired CSO. Finally, these results are consistent with general findings associated with counterconditioning experiments. For example, Williams and Barry (1966) found that operant responding for food on a variable-interval reinforcement schedule was less suppressed by contingent shocks programmed on the same schedule if the food and shocks occurred together than if food and shock were presented in a nonpaired fashion. One might expect that food-shock pairing would reduce the acquisition of fear and would result in less suppression of food reinforced responding. Thus, the results of the present experiment provide added support for the type of two-process theory which incorporates the notion of inherent incompatability between conditioned appetitive and aversive mediational states.
26
JOHN A. BULL,
III
REFERENCES J. A., III, & OVERMIER, J. B. The additive and subtractive properties of excitation and inhibition. Journal of Comparative and Physiological Psychology, 1968, 66, 511-514. COULSON, G., & WALSH, M. Facilitation of avoidance responding in white rats during a stimulus preceding food. Psychological Reports, 1968, 22, 1277-1284. ESTES, W. K., & SKINNER, B. F. Some quantitative properties of anxiety. Journal of Experimental Psychology, 194 1, 29, 390-400. GROSSEN, N. E., KOSTANSEK, D. J., & BOLLES, R. C. Effects of appetitive discrimative stimuli upon avoidance behavior. Journal of Experimental Psychology, 1969, 81, BULL,
340-343. MOWRER, 0.
H. Learning theory and behavior. New York: Wiley, 1960. RESCORLA, R. A. Pavlovian conditioning and its proper control procedures. Psychological Review, 1967,74, 71-80. RESCORLA, R. A., & SOLOMON, R. L. Two-process learning theory: Relationships between Pavlovian conditioning and instrumental learning. Psychological Review, 1967, 74, 151-182. TRAPOLD, M. A., & WINOKUR, S. Transfer from classical conditioning and extinction to acquisition, extinction and stimulus generalization of a positively reinforced instrumental response. Journal of Experimental Psychology, 1967, 73, 517-525. WILLIAMS, D. R., & BARRY, H., III. Counterconditioning in an operant conflict situation. Journal of Comparative and Physiological Psychology, 1966,61, 154-156. (Received March 3,1969)
AND
(1970) 1, 18-26
MOTIVATION
An Interaction
Between
Instrumental
Appetitive Avoidance
JOHN
A.
University
BULL,
Pavlovian Responding
CSs and ’
III2
of Minnesota
Three groups of dogs were first trained to avoid shock by responding during a visual signal. Second, these groups underwent appetitive Pavlovian conditioning operations in a different environment. Later when compounded with the cue for avoidance in transfer tests, a CS+ which had reliably signaled food presentations during Pavlovian conditioning produced marked decreases in rates of avoidance responding, while a CS” which had been presented randomly with respect to food, and a CS- which had been contrasted with food, produced no effect. This class of Pavlovian conditioning + instrumental responding interaction experiments has been the subject of theoretical controversy. These results suggest that appetitive and aversive conditioned motivational states interact subtractively.
Recent experiments have shown that Pavlovian CSs can influence and/or control instrumental responding (Trapold & Winokur, 1967; Bull & Overmier, 1968). Such experiments typically present an appetitive Pavlovian CS in an instrumental appetitive situation or present an aversive Pavlovian CS in an instrumental avoidance situation, the Pavlovian stimuli having been established by separate operations independent of the instrumental training. The rationale for this general experimental paradigm is derived from two-process theories of instrumental learning (cf., Rescorla & Solomon, 1967) in which states established by Pavlovian conditioning are thought to be important in the control and modulation of instrumental responding. Rescorla and Solomon (1967) point out the utility of such experiments in providing basic data from which a more comprehensive behavior theory may be derived, and ‘This research was supported by U. S. Public Health Service Grant MH-13558 to J. Bruce Overmier who directed the Ph.D. dissertation submitted to the University of Minnesota upon which this article is based. The author also thanks Milton A. Trapold for his comments on an earlier draft of this paper. 2 During the course of this investigation, the author was a National Institute of Mental Health Predoctoral Fellow No. I-Fl-MH-35, 727-Ol-PS. Requests for reprints should be sent to the author, Department of Psychology, The George Washington University, Washington, D. C. 20006. 18
PAVLOVIAN-INSTRUMENTAL
INTERACTION
19
they further point out that in order to develop more explicit theoretical mechanisms, data regarding the interaction between appetitive CSs and instrumental avoidance behavior would be of crucial interest. Two recent experiments have provided suggestive evidence with regard to this interaction. Coulson and Walsh (1968), using a design that was the inverse of the typical conditioned suppression experiment, superimposed a CS followed by food on an unsignaled baseline of instrumental avoidance responding in rats. They found that the CS produced a slight increase in the rate of bar press avoidance responding. These results were interpreted as being inconsistent with a general energizing or motivational effect conditioned to the CS. A second experiment has recently been described by Grossen, Kostansek, and Bolles (1969). Here, rats were first given training in a two-way shuttle box to avoid a periodic, unsignaled shock. They were then given Pavlovian conditioning trails in which, for different groups: (a) the CS was paired with food (CS+); (b) the CS signaled a period when no food would be delivered (CS-); and (c) the CS and food were presented randomly with respect to each other in time (control CSO). These groups were then tested by superimposing the CS on the instrumental avoidance response baseline. It was found that the response rate to the CS+ was lower and response rate to CS- higher than the response rate to the control CSO. Thus the appetitive CS+ depressed avoidance responding, while the CS- enhanced it. This is consistent with the view that appetitive CS+‘s somehow decrease the aversiveness of the stimuli controlling avoidance responding while the appetitive CS-‘s are themselves aversive and add to the aversiveness state controlling avoidance responding. These two experiments indicate that the scant evidence regarding appetitive + aversive interaction is inconsistent and inconclusive. In order to provide additional data, the present experiment used appetitive Pavlovian conditioning procedures to establish CS+, CS-, and CS” signals and then tested the effects of these CSs when presented in combination with a separately established SD for avoidance responding. METHOD
Subjects The Ss were 15 mongrel dogs, 15-19 in. high at the shoulder. They were obtained from the University of Minnesota animal hospital, and housed in individual cages. Ss were food deprived and maintained at approximately 80% body weight. Water was continuously available. Each S was arbitrarily assigned to one of three groups.
20
JOHN
A.
BULL,
III
Apparatus
The avoidance training apparatus was a two-way shuttlebox with two compartments separated by an l&in. barrier and a removable dropping door which isolated the two compartments. Each compartment was 45 X 24 in. and 40 in. high, with plywood walls painted flat black. Ceilings were made of hardware cloth. Above each compartment ceiling, a lo-in. high, enclosed chamber contained a 7.5 W light, a 150 W light, and two 5 X 7 double cone speakers. A one-way mirror was mounted in the front of each chamber to permit observation of the Ss. One speaker in each chamber continuously introduced approximately 70 db (re: .0002 dynes/ sq cm) of white noise into each compartment. The remaining speaker was used to present the tone CSs approximately 15 db above the continuously present white noise level. Electric shock was administered through a grid floor of la in. aluminum bars placed g in. apart. A commutator shifted the polarity patterns of the bars six times per second. The shock source consisted of a 600-V transformer to which a variable input from an autotransformer connected to 110 Vat could be applied. A current limiting resistence of 50,000 ohms was placed in series with the S and the current was continuously monitored with a meter. Trial duration was measured to the nearest .Ol set, using a standard electric timer controlled by two photocell relays placed in each compartment, 14 in. from the grid floor and 11 in. from each side of the barrier. Responses during trials as well as responses between trials were recorded using both a cumulative and an event recorder. Stimulus presentations and temporal contingencies were controlled by automatic relay circuitry, housed in an adjacent room. Pavlovian conditioning took place in a separate, partially soundproof, 5 X SQ-ft booth, 6$ ft high. The dogs were supported 30 in. above ground level by a 34 X 17-in. plywood floor in a metal frame made of l&in. pipe. This frame also supported an aluminum tray, 14 in. above the plywood floor to which was fastened a food cup. A specially designed and constructed rotary pellet dispenser was located above and to the left of the dog’s head, approximately 22 in. from the food cup. The food dispenser operated with an audible click dropping a pellet into a chute which carried the pellet to the food cup. Part of the metal frame encircled the dog about chest high, discouraging escape. The dogs were further restrained by a collar, fastened to the ceiling of the booth and to each side of the frame by a light chain, but loosely enough so that the food could easily be reached and the animals would not be unduly upset. Two 6 X 9-in. speakers introduced continuous white noise into the booth at approximately 80 db. A third 6 X 9-in. speaker introduced the tone CSs at about 15 db above the white noise level. All speakers were
PAVLOVIAN-INSTRUMENTAL
INTERACTION
21
located along the top of the back wall. The booth was illuminated by four, 12-V lamps, one located above, and three above and in front of the animals. Automatic relay circuitry, controlling stimulus presentations and temporal contingencies, was located outside the booth. Treatments Training sessions took place on consecutive days. Ss were placed in the apparatus approximately 5 min before the start of each session and removed approximately 5 min after each session and placed in their home cages. All Ss were maintained on food deprivation starting approximately 7 days before the first training session. Znstrumerztal avoidance training. In the first stage of the experiment, all Ss were trained to avoid shock by jumping the barrier in the shuttlebox. Each session consisted of 21 trials and each trial was initiated by the onset of a visual SD (switching off both 150-W lamps). If the S did not cross the barrier within 10 set (CS-UCS interval), the UCS (4.5 mA shock) was turned on and remained on until S crossed the barrier or until 50 set had elapsed and the trial terminated. Crossing the barrier terminated both the SD and UCS. A response by S within 10 set of the SD onset, terminated the trial and avoided the shock. The average intertrial interval was 120 set and ranged between 45 and 180 sec. This training was continued until a criterion (no shock) during a daily session was met. The CS-UCS interval was then shortened to 5 set and the S was again required to meet the criterion of no shocks during a session. When this criterion was met, each S was given a special second stage of instrumental avoidance training designed to build up the rate of barrier crossing through what amounts to a discrete trial variable interval schedule of reinforcement. This second stage was characterized by a variable interval (VI) hold period during which the CS was on but responses did not terminate the SD. This hold period varied and was either 0, 3, 6, 12, or 18 set long, but only three of these values were used during any one session, seven trials per session with each hold period used. At the end of the hold period, the next barrier jumping response terminated the SD. If no response was made within 5 set of the termination of the hold period, a 9-mA shock of 0.5 set duration was delivered. The schedule resulted in a stable rate of barrier jumping controlled by a discrete trial stimulus. The first sessions of this schedule involved the holds: 0, 3, and 6 sec. When a criterion of five or less shocks per daily session was met, the hold periods were changed to 0, 6, and 12 sec. When the criterion of five or less shocks was again met, the hold periods were changed to the final settings of 0, 6, and 18 sec. Training was continued until each S met a final criterion of no shocks for two consecutive daily sessions or
22
JOHN
A.
BULL,
III
until 10 days of VI-hold training had transpired, after which Pavlovian conditioning was begun. Pavlovian conditioning. In the second stage of the experiment, Ss received 21 appetitive conditioning trials per day over six consecutive daily sessions. A UCS presentation consisted of one food pellet dropped in front of the dog’s nose (Gaines: Prime pellets). Each S was placed in one of three groups. In the CS+ group, a 1200-cps tone was paired with food. In the CS- group, a 1200-cps tone was contrasted with food such that the tone signaled a period in which food would not be presented. In the CS” control group, a 1200-cps tone was presented randomly with respect to the 21 food presentations. The duration of the CS tones was either 5, 10, or 15 set, seven of each presented in random order during a session. When a CS was paired with food, the food was delivered at the termination of the CS. When a CS was contrasted with food, the food was delivered during an inter-trial interval such that a CS signaled no food for at least 40 sec. This interval varied with a maximum of 120 set and an average of 80 sec. In the random control group, the tone was programmed randomly with respect to the UCS but scheduled so that the inter-CS intervals and interUCS intervals were equal to the contingent groups in average duration and range. All groups were equated in session duration and reinforcement density, and received 21 UCS presentations per day. On the day following the last Pavlovian conditioning session, an added day of VI-avoidance training was given, exactly as before. On the day following this, testing was begun. Testing. The testing was carried out during extinction trials of the avoidance response in the shuttle box. Two types of test trials were given: (a) SD alone; and (6) 1200-cps tone and visual SD presented simultaneously (SD-plus-CS compound). Twenty-four test trials (12 of each type) were presented in random order during each of three daily sessions. Test trials for all groups were presented with an average inter-trial interval of 80 set and a range of 40 to 120 sec. Each trial used a IO-set hold period, during which responses were ineffective (as in training). The first response after the hold period terminated the trial and the test stimuli. If no response was made within 30 set after the end of the hold period, the trial and test stimuli were automatically terminated. RESULTS
Rate of barrier jumping each S on every test trial during each of the two every S. The group mean
during the IO-set hold period was recorded for and daily mean response rates (jumps/minute) test stimulus conditions were calculated for response rates under each test stimulus con-
PAVLOVIAN-INSTRUMENTAL
K a a
20
I
INTERACTION
cs+ cso
o......a
cs-
iYJ. .. . .. . .a
I
23
I
SD
sD+cs STIMULI
FIG. 1. Mean avoidance response rates (jumps/minute) condition.
for each group to each stimulus
dition are presented in Figure 1. An analysis of variance revealed a significant difference between Groups (F = 12.85, p < .Ol, df= 2/ 12) and a significant Group x Stimulus Condition interaction (F = 5.85, p < .05, df= 2/12). A comparison of means between the two test stimulus conditions within each group revealed that the decrease in response rate during the SD-plus-CS compound for the CS+ group was significant (t = 6.46, p < .Ol, u”= 12).3 The slight decrease in the CS” group was not significant while the similar decrease in the CS- group did just reach significance (t = 2.75, p < .05, df= 12). However, these decreases are confounded with any stimulus generalization decrement due to the novel presentation of the SD-plus-CS compound in the test situation [indeed, if the random control procedure provides a truly neutral CS (Rescorla, 1967), all of the decrease in the CS” group may be accounted for in this way]. Because the confounding factor may have been responsible for part of the decrease observed in the CS+ group and possibly account for all of the decrease observed in the CS” and CS- groups (which were behaviorly quite similar), means between groups were compared for the SD-plus-CS compound condition, a comparison which avoids such confounding. The large difference between the CS+ and CS” groups was significant (t= 5.51, p < .Ol, df= 12) as was the large difference between the CS+ and CS- groups (t = 5.02, p < .Ol, df= 12). The slight difference between the CS” and CS- groups was not significant. However, comparisons between group means for the baseline SD condition 3 All f tests are two tailed.
24
JOHN
A.
BULL,
III
uz. % rcs+ I 2 40
-
g 30
-
!-f 20 l2 a0 IO-
cso cs-
0 ......... 0 D.............fl
*......a g;&.:;;:;;.;~~&$:2’.yo I I
I 2
I 3
TEST DAYS 2. Means of daily percent decreases in avoidance response rates during the SDplus-CS compounds relative to the response rates during the SD alone (i.e., [SD rate - compound ratellS’ rate). FIG.
indicated that while differences between the CS+ and CS” groups as well as between the CS- and CS” groups were not significant, the difference between the CS+ and CS- groups did reach a low level of significance (t = 2.22, p < .05, df= 12). Although this slightly lower baseline rate for the CS+ group may have been due to across-trial generalization during testing of the large effect produced by the CS+ compound stimulus (an argument supported by the observation that the baseline differences increased over days), this baseline difference confounds the differences found in the SD-plus-CS condition. In order to take into account the possible confounding factors, daily percent rate decreases from baseline were calculated for each S. Group averages are presented in Figure 2. This measure compared the daily mean rate to the SD with the daily mean rate to the SD-plus-CS compound using the formula: [SD - (SD-plus-CS)]/SD. An analysis of variance indicated significant Group differences (F = 11.54, p < .Ol, df= 2/12). Between-group comparisons indicated that the percent decrease for the CS+ group was significantly greater than the CS” group (t = 4.32, p < .Ol, df= 12) or the CS- group (t = 3.98, p < .Ol, df= 12). The difference between the CS” and CS- groups was not significant. There was no significant effect of test days. DISCUSSION
A food-paired Pavlovian CS+ produced marked decreases in rate of avoidance responding when it was presented together with the SD controlling the avoidance behavior. Because similar decreases did not occur
PAVLOVIAN-INSTRUMENTAL
INTERACTION
25
to the randomly paired stimulus in the CS” control group, the results cannot be explained by stimulus generalization decrements, sensitization, or pseudoconditioning. These results strongly support the contention that a food-paired Pavlovian CS acquired mediational properties which are inherently incompatible with the mediational properties of a signal controlling avoidance responding. To the extent that the avoidance SD is also a mediational fear CS, a reduction in response rate during the presentation of a food-paired or hope CS is expected. This is consistent with Mowrer’s (1960) suggestion that CSs based on shock interact subtractively with CSs based on food and fails to support the contention that incentive functions are acquired by appetitive CSs which energize instrumental behavior regardless of the type of reinforcer involved (Coulson & Walsh, 1968). It should be noted that these experimental conditions are an inversion of the well documented conditioned suppression phenomenon (Estes & Skinner, 194 1) wherein a shock-paired CS is presented during appetitive responding. This response rate suppression produced by the shock-paired CS is also predicted by the notion of a subtractive interaction between conditioned anticipatory mediational states based on food and shock. Further, these results are consistent with those of Grossen et al. (1969) for the food-paired group. The failure of the CS- group to show an excitation effect, as did Grossen et al., is unexplained. This discrepancy could be due to species differences, procedural differences, or both. The parameters for the CS- group were selected so as to match the temporal and food density conditions of the CS+ group (as well as the CS” group), except for the CS-UCS pairing. Since little is known about optimal parameters for food contrast conditioning, it may be that the parameters used here were not sufficient for the development of any mediational state based upon absence of food. This would result in an ineffective CSwhich would act essentially the same as a randomly paired CSO. Finally, these results are consistent with general findings associated with counterconditioning experiments. For example, Williams and Barry (1966) found that operant responding for food on a variable-interval reinforcement schedule was less suppressed by contingent shocks programmed on the same schedule if the food and shocks occurred together than if food and shock were presented in a nonpaired fashion. One might expect that food-shock pairing would reduce the acquisition of fear and would result in less suppression of food reinforced responding. Thus, the results of the present experiment provide added support for the type of two-process theory which incorporates the notion of inherent incompatability between conditioned appetitive and aversive mediational states.
26
JOHN A. BULL,
III
REFERENCES J. A., III, & OVERMIER, J. B. The additive and subtractive properties of excitation and inhibition. Journal of Comparative and Physiological Psychology, 1968, 66, 511-514. COULSON, G., & WALSH, M. Facilitation of avoidance responding in white rats during a stimulus preceding food. Psychological Reports, 1968, 22, 1277-1284. ESTES, W. K., & SKINNER, B. F. Some quantitative properties of anxiety. Journal of Experimental Psychology, 194 1, 29, 390-400. GROSSEN, N. E., KOSTANSEK, D. J., & BOLLES, R. C. Effects of appetitive discrimative stimuli upon avoidance behavior. Journal of Experimental Psychology, 1969, 81, BULL,
340-343. MOWRER, 0.
H. Learning theory and behavior. New York: Wiley, 1960. RESCORLA, R. A. Pavlovian conditioning and its proper control procedures. Psychological Review, 1967,74, 71-80. RESCORLA, R. A., & SOLOMON, R. L. Two-process learning theory: Relationships between Pavlovian conditioning and instrumental learning. Psychological Review, 1967, 74, 151-182. TRAPOLD, M. A., & WINOKUR, S. Transfer from classical conditioning and extinction to acquisition, extinction and stimulus generalization of a positively reinforced instrumental response. Journal of Experimental Psychology, 1967, 73, 517-525. WILLIAMS, D. R., & BARRY, H., III. Counterconditioning in an operant conflict situation. Journal of Comparative and Physiological Psychology, 1966,61, 154-156. (Received March 3,1969)