that classes of behavior are produced accord- .... Key pecks made by pigeons exposed to the FI or auto- ...... Williams, D. R., & Williams, H. Auto-maintenance in.
1980, 34, 1-12
JOURNAL OF THE EXPERIMENTAL ANALYSIS OF BEHAVIOR
NUMBER
I (JULY)
THE ROLE OF CONTINGENCIES AND "PRINCIPLES OF BEHA VIORAL VARIA TION" IN PIGEONS' PECKING DOUGLAS FENNER DICKINSON COLLEGE
Staddon and Simzmelhag's proposal that behavior is produced by "principles of behavioral variation" instead of contingencies of reinforcement was tested in two experiments. In the first experiment pigeons were exposed to either a fixed-interval schedule of response-contingent reinforcement, an autoshaping schedule of stimulus-contingent reinforcement, or a fixed-time schedule of noncontingent reinforcement. Pigeons exposed to contingent reinforcement came to peck more rapidly than those exposed to noncontingent reinforcement. Staddon and Simmelhag's "principles of behavioral variation" included the proposal that patterns (interim and terminal) were a function of momentary probability of reinforcement. In the seconid experiment pigeons were exposed to either a fixed-time or a randomtime schedule of noncontingent reinforcement. Pecking showed a constant frequency of occurrence over postfood time on the random-time schedule. Most behavior showed patterns on the fixed-time schedule that differed in overall shape (i.e., interim versus terminal) from those shown on the random-time schedule. It was concluded that both the momentary probability of reinforcement and postfood time can affect patterning. Key words: response-reinforcer contingency, stimulus-reinforcer contingency, momentary probability of reinforcement, postfood time, interim, terminal, random-time schedules of reinforcement, pecking, pigeons
Staddon and Simmelhag (1971) have pro- pecking was the same whether the pigeons posed a theory of behavior based on an anal- were exposed to response-dependent or reogy with Darwinian evolution. They proposed sponse-independent food. When the food was that classes of behavior are produced accord- response dependent, most of the pecks struck ing to "principles of behavioral variation," the response key, but when the food was and that "principles of reinforcement" de- response independent, the location of the scribe the selective elimination of some classes. pecks was more variable. Staddon and SimFurther, they reported an experiment which melhag conclude that: according to their analysis showed that the This result raises the possibility that the pecking of pigeons on interval schedules of effect of the response-dependency, in opreinforcement is produced according to prinerant conditioning experiments using inciples of behavioral variation rather than by terval reinforcement schedules, may be contingencies of reinforcement. They exposed one of determining (perhaps imlargely pigeons to response-dependent and responsethe location of pecking, rather perfectly) independent schedules of food presentation than either its form or its frequency of while an observer recorded a variety of reoccurrence. (p. 13) [their emphasis] sponses. It was found that the probability of On an empirical level, then, Staddon and data indicate that response-deSimmelhag's The author wishes to thank D. R. Williams, A. Neuringer, D. R. Thomas, R. Newlin, James Rogers, Peter pendencies or contingencies do not affect the Killeen, and Jon Williams for their helpful comments asymptotic frequency observer-recorded peckon this study, and D. Evans for typing the manuscript. Supported in part by NSF Grant GB 35319X to D. R. Williams, NIH Grant HD-03486 to D. R. Thomas, and an NSF Graduate Fellowship to the author. Portions of this study were conducted at the University of Pennsylvania and the University of Colorado. Reprints may be obtained from Douglas Fenner, Psychology Department, Dickinson College, Carlisle, Pennsylvania
ing by pigeons. On a theoretical level Staddon and Simmelhag (1971) consider the response-dependent and response-independent schedules to differ with respect to the selective principle of reinforcement. They write that "if reinforcement is considered as purely selective, it cannot be
17013.
1
2
DOUGLAS FENNER
invoked as an explanation of behavior when no imposed contingency exists between reinforcement and behavior (i.e., in the absence of selection)" (Staddon & Simmelhag, 1971, p. 21, emphasis theirs). And "If there is no contingency, or if few contingent reinforcements have occurred, the resulting behavior must owe more to principles of variation than to the selective action of reinforcement" (Staddon & Simmelhag, 1971, p. 21). Staddon and Simmelhag reject the view that a reinforcer automatically strengthens any operant which precedes it, and instead propose that the ability of reinforcers to select types of behavior is directly dependent upon the presence of response-reinforcer contingencies or dependencies. According to their view response-independent schedules of food delivery contain no contingencies, and thus, the behavior produced by such a schedule cannot have been influenced by selection. Instead, such behavior must be produced by principles of variation. Their experiment indicates that pecking was equally probable on response-dependent and independent schedules, and thus they suggest that pecking is produced according to principles of variation and only its location is affected by the selective action of reinforcement. Staddon and Simmelhag's (1971) finding that a great deal of pecking occurs on noncontingent schedules could also be seen as a problem for the view that the keylight-food contingency in autoshaping (Brown & Jenkins, 1968) affects the frequency of pecking. It is possible that the contingency serves only to direct pecking toward the key. This in turn suggests that autoshaping is not related to classical conditioning, since the only effect of autoshaping may be to direct pecking, an effect which "does not follow naturally from respondent principles" (Williams 8c Williams, 1969). Thus, Staddon and Simmelhag's findings could be interpreted as a problem for the position that autoshaping involves the "classical conditioning of a comolex skeletal resnonse" (Gamzu &c Williams, 1971). The first experiment reported here attempts to determine whether response-reinforcer and stimulus-reinforcer contingencies can affect the rate of pecking relative to the noncontingent presentation of reinforcers. In the second experiment a test is made of Staddon and Simmelhag's (1971) proposal that behavior is pro-
duced by certain "principles of behavioral variation," instead of by contingencies of reinforcement. In particular, a test is made of their proposal that terminal behavior occurs when reinforcement is probable, and interim behavior occurs when reinforcement is improbable. EXPERIMENT 1 The first experiment was designed to replicate Staddon and Simmelhag's (1971) finding that response-reinforcer contingencies do not affect the frequency of pigeons' pecking. The schedules used for response-contingent and noncontingent reinforcement were fixed-interval 12-sec (Fl 1 2-sec) and fixed-time 12-sec (FT 12-sec), respectively, since these schedules were used by Staddon and Simmelhag (1971). In addition, an autoshaping schedule was used for keylight-contingent reinforcement with the same period of time between successive reinforcers (12 sec) as in the FI and FT schedules. An observer recorded all pecks made by the birds exposed to noncontingent reinforcement, since Staddon and Simmelhag (1971) reported that noncontingent reinforcement produces many pecks which are not directed at the key. White Carneaux pigeons were used, as in Staddon and Simmelhag (1971). METHOD
Sutbjects Twelve White Carneaux pigeons, all experimentally naive, served. All were obtained from Palmetto Pigeon Plant of Sumter, South Carolina, and were held at 80% of their free-feed-
ing weighlts. Apparatus The exneriment was conducted in a Lehigh Valley Electronics three-key operant conditioning chamber measuring 30 cm by 34 cm by 35 cm. To facilitate observation the cham. ber was lit during sessions of noncontingent reinforcement with both the houselight supplied with the chamber, and a 15-W 110-V frosted light bulb. The 110-V bulb was suspended in the upper corner of the chamber adjoining the door, farthest from the magazine. The three keys were covered with masking tape in these sessions. During sessions of FI reinforcement of autoshaping, the cham-
CONTINGENCIES AND PRINCIPLES OF VARIATION
3
Four birds were exposed to an Fl 12-sec ber was illuminated by only the houselight supplied with the chamber, and the center schedule of key-peck-contingent reinforcement. key was uncovered. Subjects exposed to non- These birds were hand-shaped to peck a red contingent reinforcement were observed key in the session following magazine trainthrough a one-way window in the door of ing, and then given 35 15-min sessions of FI the chamber. Responses were recorded man- 12-sec. For all groups reinforcers consisted of ually by pressing microswitches attached to 5 sec access to grain. A second group of four an Esterline Angus event recorder with a birds was exposed to response-independent aupaper speed of 7.5 cm/min. The classes of toshaping following magazine training. Folresponses recorded are presented in Table 1. lowing a 1 0-sec period with a dark key, a Most of the response classes were derived from green keylight came on for 2 sec, and was those of Staddon and Simmelhag (1971) with- followed by a 5-sec grain presentation. Key out modification. However, instead of record- pecks had no programmed consequences. The ing locomotion as a continuous activity, each birds were exposed to this condition for 35 step was recorded as a discrete response. In 50-reinforcer sessions. A third group of four addition, more complex species-specific behav- birds was exposed to an FT 12-sec schedule of ior such as that described by Miller and Miller noncontingent reinforcement for 35 50-rein(1958) were included in a single category with forcer sessions. The key was covered with wing-flapping, since these activities occurred masking tape during these sessions. On about infrequently. Pecks from outside of the maga- every fifth session, an observer recorded the zine that were directed into the magazine were behavior of birds exposed to the FT schedule. included in RI with pecks on the magazine RESULTS wall, not with R8, head in magazine. Only reTable 2 presents the rate of pecking for sponses 1, 2, and 3 (pecks magazine wall, pecks any other wall, and pecks floor, respectively) the White Carneaux exposed to the FI 12-sec, are relevant to this experiment. Key pecks autoshaping, and FT 12-sec schedules. For made by pigeons exposed to the FI or auto- birds exposed to FI, "pecking" consisted of shaping schedules were recorded by standard all observer-recorded pecks (responses 1, 2, and electromechanical devices. 3). For birds exposed to Fl or autoshaping, "pecking" consisted of key pecks. Both the Procedure average rate of pecking throughout the session Magazine training was carried out in one ("session pecking") and the rate of pecking in session; there were no habituation sessions. the 11th and 12th sec following grain presenThe magazine was raised before the pigeon tations ("terminal pecking") are presented. was introduced into the chamber, and kept up Session pecking was averaged over all recorded until the bird ate. The session was terminated sessions, but terminal pecking was averaged after the pigeon had eaten from the magazine over only the last two recorded sessions since for 50 presentations. One bird (C6) that was these data were available only for the last especially difficult to magazine train was given two sessions. The data in Table 2 indicate that five additional sessions of magazine training. birds exposed to Fl and autoshaping schedules pecked at higher rates than did the birds exTable 1 posed to the FT schedule. These differences Types of Behavior Recorded were particularly clear for the terminal pecking. These impressions were confirmed by a 1. Pecks magazine wall. 2. Pecks any other wall. 3 x 2 analysis of variance, with repeated mea3. Pecks flpor. sures of the session pecking versus terminal 4. Body faces magazine wall. pecking variable. There was reason to ques5. Body faces window wall. tion the assumption of homogeneity of variother faces wall. 6. Body any 7. Makes full circle turn. ance, so a Geisser-Greenhouse conservative F 8. Head in magazine. test was used (Kirk, 1968). There was a signifi9. One step taken with either foot: foot lifted and placed on cant effect of schedule [F(2,9) = 25.9, p < .01], floor. 10. Wing-flapping; aggressive behavior such as bow-coo or a significant effect of session versus terminal wing whack; comfort movements such as stretches, head pecking [F(l,9) = 27.5, p < .01], and a signifishakes, and tail wags. cant interaction [F(2,9) = 10.3, p < .01]. Analy-
DOUGLAS FENNER
4
Table 2 Rate of pecking by White Carneaux pigeons exposed to FI 12-sec, autoshaping, and FT 12-sec schedules. 'Session pecking' is the average rate of pecking throughout the session (reinforcement time subtracted); 'terminal pecking" is the average rate of pecking in the 11th and 12th sec following grain presentations. Rates for FI 12-sec and autoshaping are for key pecks only; rates for FT 12-sec are for all observer-recorded pecks.
FI 12-sec Session Terminal
Autoshaping Session Terminal
FT 12-sec
Session
Bird
pecking
pecking
Bird
pecking
pecking
Bird
pecking
I1 12 I3 14 mean
32.6 35.3 39.5 44.3 37.9
70.1 80.5 136.2 120.6 101.9
Al A2 A3 A4
1.1 11.4 3.1 15.3 7.7
5.4 62.8 18.4 48.7 33.8
C5 C6 C7 C8
.2 .01 .7 .1 .28
sis of the simple main effects showed that there was a significant effect of schedule for the terminal measure [F(2,18) = 36.0, p < .01]. Tukey's HSD test was used for comparing individual means. The birds exposed to FI had a higher rate of terminal pecking than birds exposed to autoshaping (q' = 7.9, p < .01), which in turn had a higher rate of terminal pecking than the birds exposed to FT (q' = 3.9, p < .05). The birds exposed to FI also pecked at a higher rate throughout the session than FT birds (q' = 4.4, p < .05), though the
remaining pairwise comparisons of session pecking were not significant. Thus, higher rates of pecking were produced by the response-contingent (FI 12-sec) and stimulus-contingent (autoshaping) schedules than by the noncontingent (FT 12-sec) schedule, particularly in the last 2 sec before reinforcement. Further, the results obtained may have underestimated the differences, since only key pecks were recorded during contingent reinforcement, while all pecks were recorded during noncontingent reinforcement. It is quite likely that some of the pecks emitted by the birds exposed to contingent reinforcement did not operate the key, so that the rate of key pecks recorded underestimated the total rate of pecking. DISCUSSION The results of the present experiment fail to replicate Staddon and Simmelhag's (1971) finding that response-contingent and noncontingent grain presentations produce equal frequencies of pecking by pigeons. In the present experiment pigeons exposed to response-contingent reinforcement pecked at much higher rates than pigeons exposed to noncontingent
Terrminal
pecking .4 .09 2.0 .09 .65
reinforcement. Likewise, the pigeons exposed to stimulus-contingent reinforcement pecked at higher rates than did the pigeons exposed to noncontingent reinforcement. Thus, this experiment indicates that contingencies can increase the frequency of pecking as well as influence their location. Possible reasons for the failure to replicate Staddon and Simmelhag's (1971) findings will be deferred to the general discussion which follows the second experiment. The pigeons in Experiment 1 that were exposed to response-contingent reinforcement pecked at higher rates than the pigeons that were exposed to stimulus-contingent reinforcement. However, there are a number of reasons why this should not be taken to indicate that response contingencies have stronger effects upon pecking than stimulus contingencies. First, the stimulus contingency is not positive during the intertrial interval, and thus pecking is not expected to occur until the last 2 sec before food delivery, when the keylight is on. Second, the rate of pecking during the CS can be manipulated by the duration of the CS (Perkins, Beavers, Hancock, Hemmendinger, Hemmendinger, & Ricci, 1975), which was arbitrarily set at 2 sec in this experiment. A different choice of CS duration probably would have altered the results. And third, the pigeons exposed to autoshaping may have required the first second or so of the keylight presentation to reach the key and begin pecking. The pigeons exposed to response-contingent reinforcement may have been able to peck the key more times in the last 2 sec because they were already engaged in pecking the key when the last 2 sec arrived. Thus, the results of this experiment cannot be taken as a clear indica-
CONTINGENCIES AND PRINCIPLES OF VARIATION tion that response contingencies are more effective in controlling pecking than stimulus contingencies. EXPERIMENT 2 Staddon and Simmelhag (1971) proposed that behavior is not produced by contingencies of reinforcement, but instead is produced according to several "principles of behavioral variation." Behavior that occurs late in the interreinforcement interval (and thus shows what they called a terminal pattern) occurs only when reinforcement is probable, and is governed by the "stimulus substitution" principle. Pecking was found to be such an activity in their study. Behavior that occurs early in the interreinforcement interval (and thus shows what they called an interim pattern) occurs only when there is a low probability of reinforcement. Such behavior is governed primarily by the reciprocal interaction of motivational systems (states). "Turning circles" was one such behavior in their study. Thus, Staddon and Simmelhag (1971) proposed that the behavior observed with noncontingent reinforcement is primarily of two types, distinguishable by their patterns in the interreinforcement interval (interim and terminal). Staddon and Simmelhag (1971) proposed that terminal and interim behavior occurs when reinforcement is probable or improbable, respectively. More recently, Staddon and Ayres (1975) proposed that the temporal distribution of behavior is determined by postfood time. In the experiments reported in both of these studies, the probability of reinforcement was a function of postfood time. That is, the probability of reinforcement was zero immediately following a reinforcer, and increased over the interreinforcement interval. This was true even in Staddon and Simmelhag's (1971) VT 8-sec schedule, since it had a minimum interreinforcement time of 3 sec. Thus, the interim and terminal patterns observed in these studies could have been a function of either the momentary probability of reinforcement or postfood time. The contribution of these two factors can be assessed by observing the temporal patterning produced by a random-time schedule of food deliveries. This is possible because when a probability generator is used to produce a random-time
5
schedule, the probability of food does not vary with postfood time, but is constant. If a response is controlled only by the probability of food delivery, it should show a constant frequency or probability over postfood time on a random-time schedule. However, if a response is controlled only by postfood time, it should show an interim or terminal pattern on the random-time schedule. In fact, such behavior should show the same temporal pattern on a random-time schedule as on a fixed-time schedule, since the differences in reinforcement probability between these two schedules is not a controlling factor for such behavior. Thus, recording behavioral patterns over random-time and fixed-time schedules allows assessment of the contribution of the momentary probability of food and postfood time to the patterning observed. In addition to assessing the roles of reinforcement probability and postfood time in the production of behavioral patterning, Experiment 2 tested the generality of the finding of Experiment 1 that noncontingent reinforcement produces low rates of pecking. The generality of that finding was tested across schedules of noncontingent reinforcement and across strains of pigeons. Experiment 2 utilized both the FT 12-sec schedule which was used in Experiment 1 and a random-time 12.5 sec (RT 12.5-sec) schedule which was used to test the roles of reinforcement probability and postfood time in the production of patterning. In addition three strains of pigeons were used. The biological emphasis of some recent views of behavior such as Staddon and Simmelhag's (1971) suggests that behavior may not only be species-specific, but that strain differences may also occur. Strain differences in pecking have been shown by Blanchard and Honig (1976), who found that King pigeons pecked more than Carneaux during autoshaping. The generality across strains of the low rate of pecking found in Experiment 1 was tested in Experiment 2 by using White King and Silver King pigeons in addition to White Carneaux pigeons. METHOD
Subjects Eight White King, eight Silver King, and four White Carneaux pigeons, all experimentally naive, served. All were obtained from Palmetto Pigeon Plant of Sumter, South Caro-
6
DOUGLAS FENNER
time blocks following time 0 is reported. In the present study the point representing the 0- to 2-sec time block is plotted in the middle Apparatus of that time block. It seems quite likely that The same chamber and recording apparatus in Staddon and Simmelhag's (1971) study, bewas used in Experiment 1, with the keys and havior such as facing the magazine wall or houselight arranged for noncontingent rein- head in magazine occurred frequently when forcement as in that experiment. Random in- the magazine was lowered (time 0). The prestervals for the RT 12.5-sec schedule were gen- ent method of plotting avoids making the imerated by having a clock deliver a pulse every pression that a response shows a terminal pat.5 sec to a Scientific Prototype model 4020J tern when in fact it may have been at a high probability generator set a P = .04. The out- probability at all times. put of the probability generator operated the Only the responses which occurred suffifeeder timer directly. ciently often to analyze their temporal pattern are shown in Figure 1. Some behavior showed Pr-ocedure little or no patterning over postfood time. FacMagazine training was carried out as in ing the magazine wall (R4) showed a very Experiment 1. The pigeons were divided into constant, high probability over postfood time groups according to a 3 x 2 factorial design. for birds C3, C4, S3, S4, WI, W2, W3, and W4. The factorial design consisted of three strains Pecking the magazine wall (RI) showed a relaof pigeons (White King, Silver King, and tively constant probability over postfood time White Carneaux) and two schedules of non- for bird S3, S4, and WI, as did stepping (R9) contingent reinforcement (FT 12-sec and RT for bird W2. In only a few cases did an activity 12.5-sec, the RT schedule being 12.5 instead show clear changes in probability over most of 12 due to the probability generator). There of the postfood time in Figure 1: facing the were four birds per cell. The data for the cell window wall (R5) and stepping (R9) for the containing White Carneaux exposed to the bird Cl, and facing any other wall (R6) and FT 12-sec schedule came from the data ob- turning a circle (R7) for bird S4. Most activities tained from the four White Carneaux exposed showed clear changes in probability over the to FT 12-sec in Experiment 1. All of the birds first 2 or 4 sec of postfood time, and then a were given 50 5-sec grain presentations per relatively constant probability after that. Facsession for 35 sessions. An observer recorded ing the window wall (R5) showed this pattern behavior about every fifth session as in Ex- for birds C2, SI, S2, S4, and W4. Facing any periment 1. Response rates were calculated other wall (R6) showed this pattern for bird from the total number of responses and time S1, and stepping (R9) showed it for birds C2, (minus reinforcer duration), and probabilities SI, S2, S3, S4, and W4. Of the activities showwere arrived at by tabulating whether each ing changes in probability over postfood time 2-sec interval contained any responses, or not. most showed terminal patterns, though a few The same was true in Experiment 1. (R4 and R9 for bird S2; R6 and R7 for bird S4) showed interim patterns. RESULTS A comparison of the patterns produced by Figure 1 shows the probability of types of RT and FT schedules can be made by referbehavior over postfood time for the 12 pigeons ence to the data in Figure 2. Figure 2 shows exposed to the RT schedule. The data pre- the mean probability of types of behavior over sented are the means of the last two recorded postfood time. The left-hand panel presents sessions. The method of plotting differs some- the means for the birds exposed to the FT what from that used by Staddon and Simmel- schedule and the right-hand panel presents the hag (1971). Their figures show the probability means for the birds exposed to the RT schedof all responses to be 0 at 0-sec postfood time ule. The data presented are the means of the (when the magazine was lowered). In the pres- last two recorded sessions. The responses which ent study, as in those of Staddon and Ayres are not presented occurred too infrequently (1975) and Anderson and Shettleworth (1977), for analysis. Response 1 showed a terminal the probability of response at time 0 is not pattern on the FT schedule, as did Responses reported; only the probability of response in 5, 6, and 9 on the RT schedule. Responses lina, and were held at 80% of their free-feeding weights.
CONTINGENCIES AND PRINCIPLES OF VARIATION
WHITE CARNEAUX C2 C3
C1
1.0-
oR9
oOoR4
V0o0 5 9
T6 SILVER KINGS
Cd.' m
I
C4
o-o-o-o-oR4
I
'...
S3
Lai'
S4 4 9
=
9
5
5 4 6
C=
-a
6 1 ,7 WHITE KINGS
.8.6.4.2-
4
4
9 1
1
9 4
8 12
7
4
I
W3
o-"-o-o-o-o
4V 8 12 4 8 POST-FOOD SECONDS
12
4
I
W4 C
g
8 4 5
4 8 12
Fig. 1. The momentary probability of response over postfood time for the 12 pigeons exposed to the RT schedule. The data presented are the means of the last two recorded sessions. Each point presents the probability (frequency/opportunities) of a response occurring within a 2-sec block.
5, 6, and 9 showed interim patterns on the FT schedule, and Response 1 showed a constant-probability pattern on the RT schedule. Response 4 showed an interim pattern on the RT schedule, and a pattern on the FT schedule whiclh does not readily fall into either interim or terminal categories. Thus, Response 1 was the only behavior showing a constantprobability pattern on the RT schedule as
had been predicted from Staddon and Simmelhag's (1971) analysis. The temporal patterning of the behavior seen in Figure 2 was further analyzed by a 2 x 3 x 6 (schedules by strains by time blocks) analysis of variance. There were repeated measures of the 6 2-sec time blocks of postreinforcement time. There was reason to question the assumption of homogeneity of variance for
DOUGLAS FENNER
8 IT
\~~~-~~ 14 19
me RS
a-
R1~~~~~R R 6C
4
12 S 4 12 SECONDS Fig. 2. The momentary probability of five different responses over postfood time. The left-hand panel shows the average probability for the 12 pigeons exposed to the FT schedule, and the right-hand panel shows the average probability for the 12 pigeons exposed to the RT schedule. Means are for the last two recorded sessions. 8
Table 3 Rate of observer-recorded pecking during the 11th and 12th sec following each reinforcer, averaged over all recorded sessions, in Experiment 2.
White Cameaux Pecks per Bird minute
Silver Kings Pecks
White Kings Pecks
per Bird minute
Bird minute
per
C1 C2 C3 C4
0 1.0 RT 0 0 mean .25
Si S2 S3 S4
.3 1.1 .9 1.9 1.1
WI W2 W3 W4
12.1 31.3 10.0 0 13.4
C5 .3 C6 0 FT C7 1.6 C8 .08 mean .5
S5 S6 S7 S8
7.6 1.7 8.7 2.2 5.1
W5 W6 W7 W8
38.8 26.6 .2 4.9 17.6
for the 24 pigeons exposed to noncontingent reinforcers. The data in Table 3 are arranged according to the factorial design, with three responses 1, 4, and 6, so Geiser-Greenhouse strains of pigeons (White Carneaux, Silver conservative F tests were used. The results Kings, and White Kings) and two schedules for all 5 responses were quite similar, and so (FT 12-sec and RT 12.5-sec). A few of the will be presented together. There was a sig- White Kings pecked at moderate rates, but nificant effect of strain only for Response 1, all other birds pecked at low rates. An analypecking the magazine wall [F(2,18) = 8.3, p < sis of variance showed that the effect of strain .01]. The effect of time blocks was significant was significant [F(2,18) = 6.03, p < .01], but for each of the five responses [F(1,18) = 7.49, the effect of schedule [F(1,18) = .56, p < 1] 6.06, 4.87, 5.05, and 9.48 for Responses 1, 4, 5, and the interaction [F(2,18) = .12, p < 1] were 6, and 9, respectively, and all p's < .05]. The not. Tukey's test showed that the White Kings schedule by time block interaction was sig- pecked at a higher rate than both the White nificant for each activity except Response 4 Carneaux [q(3,18) = 4.6, p < .05] and the Sil[F(l,18) = 7.79, 2.37, 11.1, 8.81, 11.58, p's < .05, ver Kings [q(3,18) = 3.8, p < .05]. However, .25, .01, and .01, respectively]. None of the the Silver Kings did not peck significantly other main effects or interactions were signifi- more than the White Carneaux (q(3,18) = .82, cant. The finding that the probability of behav- p < 1]. The same pattern of results was obior was constant over time blocks only for Re- tained by using the average rate of pecking sponse 1 (pecking magazine wall) was confirmed throughout sessions, except that the difference by an anaylsis of the simple main effects of time between White Kings and Silver Kings did not blocks for each schedule. For Response 1 on quite reach significance. These results show the RT schedule, the effect of time blocks that the very low rates of pecking by White was not significant [F(1,18) = .58, p < 1]. How- Carneaux on the FT 12-sec schedule found in ever, for Response 1 on the FT schedule and Experiment 1 are generalizable to the RT 12.5for each of the other responses on both FT and sec schedule and to the Silver King pigeons, RT schedules, there was a significant effect but not to the White King pigeons. of time blocks [F(1,18) = 6.8, p < .05, at least]. The question of whether asymptotic rates of The generality of the low rates of pecking pecking were achieved in the 35 sessions of produced by the FT schedule in Experiment this experiment can be addressed by refer1 to other strains and schedules can be as- ence to Figure 3. Figure 3 plots the mean rate sessed by reference to the data presented in of pecking (regardless of the pecks' location) Table 3. Table 3 presents the rate of pecking during each session for each bird in this exduring the 11th and 12th sec following each periment. It can be seen that while a few reinforcer, averaged over all recorded sessions pigeons (e.g., W5, W8, WI, and W3) increased
CONTINGENCIES AND PRINCIPLES OF VARIATION FT
21
CS.
Cl*
CS'
Cs-Co*
IT Cl.
56
WuNI
CA.ux
CS'
Si.
Si. lo
C3.
£2
S
£3'. S
I'SILVER
S-
21
S.4
WS*
WI'
wi.
W3'
W6-
WS -
W2'
WV'
SESSI@"K
2
is
25
is SESSIINS
Is
2S
is
Fig. 3. The rate of observer-recorded pecking plotted sessions. Curves for birds exposed to FT are in the left-hand panels, and curves for birds exposed to RT are in the right-hand panels. Curves for White Carneaux are in the top panels, Silver Kings in the middle panels, and White Kings in the bottom panels. over
pecking across sections, most did not. A few pigeons reached their maximum rate of pecking in early sessions, and showed decreasing rates of pecking subsequently (e.g., S5, S8, and W2). Thus, the trends observed indicate that running further sessions would not have led to increased rates of pecking. One observation concerning pecking by the birds exposed to noncontingent reinforcement deserves mention. It was observed that only three birds (S4, S3, and W3) directed their pecks within the magazine. They held their heads outside the magazine, and pecked toward the back wall of the magazine. This pattern was easily discriminable from the pattern of pecking during a reinforcer, when the head was held inside the magazine, and pecking directed downward toward the grain. DISCUSSION The results of these two experiments support the position that response-reinforcer and stimulus-reinforcer contingencies can produce higher rates of pecking by pigeons than are produced by noncontingent reinforcers presented at the same frequency. The results do not support Staddon and Simmelhag's (1971) suggestion that response-reinforcer contingencies do not affect the frequency of a pigeon's pecking, but only determine the location of those pecks. Thus, in Experiment 1 the four
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naive White Carneaux which were exposed to the Fl 12-sec schedule of response-contingent reinforcement pecked at a reliably higher rate than the four naive White Carneaux exposed to the FT 12-sec schedule of noncontingent reinforcers. In fact, there was no overlap between the rate of terminal pecking by White Carneaux exposed to FI 12-sec in Experiment 1 (Table 2) and the rate of pecking by all of the birds exposed to noncontingent reinforcers in Experiment 2 (Table 3). The same was true of session pecking. That is, even though there were differences between strains in the rate of pecking produced by noncontingent reinforcement, none of those birds pecked as rapidly as the White Carneaux which were exposed to response-contingent reinforcement. Further, since only key pecks were recorded for the birds given response- or stimulus-contingent reinforcers, the reported rates of pecking probably underestimate the total rate of pecking by those birds. Thus, the reported difference in the rate of pecking produced by contingent and noncontingent reinforcement may underestimate the difference actually present. The acquisition data presented in Experiment 2 indicates that the different rates of pecking produced by contingent and noncontingent food in Experiment 1 were not a result of insufficient sessions for acquisition of pecking by pigeons exposed to noncontingent reinforcement. Many pigeons in Experiment 2 showed clear signs of having reached asymptotic rates of pecking before the last session, and those asymptotic rates were always less than the rates found with response-contingent reinforcement in the first experiment. In Experiment 1 it was found that birds exposed to stimulus-contingent reinforcement (autoshaping) pecked at a higher rate than birds exposed to noncontingent reinforcement. Thus, autoshaping can increase the frequency of pecking as well as direct pecking. The finding that autoshaping can increase the frequency of pecking is consistent with the view that autoshaping represents a form of classical conditioning. There are at least two possible reasons why the present attempt failed to replicate Staddon and Simmelhag's (1971) findings. One possibility arises from the fact that two of the four birds which Staddon and Simmelhag (1971) exposed to noncontingent reinforcement had
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DOUGLAS FENNER
previously had experimental experience. Pre- forcers act to selectively eliminate behaviors sumably that experimental experience in- instead of to increase the frequency of behavcluded key-peck training with response-con- iors. It might be noted that one need not tingent reinforcement. Several studies have base behavior theories on the view that evolushown that key pecking which is produced tion is produced by the selective elimination with contingent reinforcement may be main- of individuals; differential reproduction rates tained to some degree by noncontingent rein- could also produce evolution in the absence of forcement (e.g., Fenner, 1969; Herrnstein, selective elimination of individuals. 1966; Lowe & Harzem, 1977; Neuringer, 1970; The factorial design in Experiment 2 asShoenfeld, Cole, Lang, & Mankoff, 1973; Zeiler, sessed the generality across strains of pigeons 1968). Thus, for two of Staddon and Simmel- and schedules of reinforcement of the low hag's (1971) birds, noncontingent reinforce- rates of pecking found with White Carneaux ment may have maintained pecking which was on the FT schedule. The difference between originally produced by response-contingent re- the rate of pecking on the FT and RT schedinforcement. However, the behavior of the ules was small and not significant. The fact naive birds was not noticeably different from that birds pecked on the RT schedule indithe experienced birds. cates that pecking was not produced by a A second possible reason for the failure to correlation or dependency (nonrandom relareplicate is the difference between the depen- tion) between pecking and the reinforcer, since dent variables used, probability and rate of such a correlation is impossible on an RT response. Staddon and Simmelhag's (1971) schedule. It is also impossible for Pavlovian measure, probability per second, reaches a temporal conditioning to affect pecking on maximum of 1.0 at as little as 60 responses per the RT schedule, since food is delivered ranminute. Response rate is unbounded, and re- domly over time. The finding that there were mains a sensitive measure at higher rates. differences between the strains in the rate of Thus, since Staddon and Simmelhag's pigeons pecking indicates that caution should be exerpecked at probabilities approaching 1.0, dif- cised in generalizing the present results to ferences in response rate between those exposed other strains or species. Blanchard and Honig to contingent and noncontingent reinforce- (1976) found evidence which suggests that ment might have gone undetected. However, White King pigeons may peck at higher rates they still appear to have recorded more peck- during autoshaping than White Carneaux do. ing under noncontingent schedules than the This in turn suggests that White Kings may present study, since the pecking of only 2 out peck at higher rates than White Carneaux on of 24 pigeons (W5 and W6) approached a contingent schedules as well as on noncontinprobability of 1.0 per 2 sec and many were gent schedules. Thus, the finding that remuch less (Fig. 1). sponse- and stimulus-reinforcer contingencies Although the present results do not repli- led to higher rates of pecking by White Carcate Staddon and Simmelhag's (1971) finding neaux than did noncontingent reinforcement of high frequencies of pecking on noncontin- may also be found to hold for other strains in gent schedules, the results are more similar future research. to the report of Reberg, Innis, Mann, and Experiment 2 assessed the contribution of Eizenga (1978). In their first experiment they the momentary probability of reinforcement reported that only three of five birds exposed and postfood time to the production of interim to an FT 15-sec schedule pecked the walls, and terminal patterns. This was done by floor, or magazine as a terminal behavior. recording the temporal patterning of behaviors Thus, the more general finding would seem to on a schedule in which the probability of rebe that although some pigeons peck at high inforcement does not vary with postfood time, rates on noncontingent schedules, many do a random-time schedule. Any patterning which not, and the addition of contingencies can occurred on such a schedule would have to further increase those pecking rates. be due to postfood time, not the momentary It should be noted that while the present probability of reinforcement. Examination of results indicate that contingencies affect the the temporal patterning of behaviors produced rate of pecking, they do not speak to Staddon by individual pigeons on the random-time and Simmelhag's (1971) proposal that rein- schedule revealed that some behaviors showed
CONTINGENCIES AND PRINCIPLES OF VARIATION patterning, with both interim and terminal patterns represented. This indicates that postfood time does indeed affect the patterning of behaviors as Staddon and Ayres (1975) suggested. It was clear both from the individual patterns and the average pattern for birds exposed to this schedule that the strongest effects of postfood time occurred just following food, and diminished with additional postfood time. The explanation of the strong effects of postfood time over the first few seconds following food may lie in the types of behaviors which occur during food presentations. That is, during the food presentation, pigeons typically are facing the magazine wall with their heads in the magazine, pecking at the grain located there. When the magazine is lowered, the pecking stops and the head is quickly removed from the magazine. At this point the pigeon stands facing the magazine wall. Figures 2 and 3 show that the probability of facing the magazine wall (R4) is very high and the probability of facing the window wall (R5) or any other wall (R6) is very low immediately following grain presentations. The fact that the probability of facing the magazine wall typically went down over the first few seconds following grain presentations and the probability of facing the window wall or other walls went up reflects the fact that it takes a few seconds for a bird to move from the magazine to any other direction. Thus, the patterning of the three wall-facing behaviors is directly attributable to the behaviors required to consume the re-
inforcer. If postfood time were the only factor producing temporal patterning, then the patterns found with a fixed-time schedule should be the same as those found with a random-time schedule. That is, the changes in momentary probability of reinforcement over postfood time on the fixed-time schedule should have no effect. However, the patterns produced by the fixed-time schedule differed greatly from the patterns on the random-time schedule. This indicates that the momentary probability of reinforcement may well contribute to the production of patterning in the fashion proposed by Staddon and Simmelhag (1971). This is also supported by the average pattern which pecking the magazine wall (RI) showed on the random-time schedule. That is, RI showed a constant-probability pattern on the RT schedule, indicating that it was not controlled by
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postfood time, but instead by the momentary probability of reinforcement. The results of the present study indicate that the temporal patterning of behaviors on noncontingent schedules is multiply determined. Patterning in the first few seconds following food presentations may be controlled by postfood time. Thus, several behaviors showed increasing probabilities of occurrence over the first few seconds following food on both random- and fixed-time schedules. Patterning later in the interreinforcement interval may be controlled by the momentary probability of reinforcement. The average probability of all behaviors was constant after the first couple of sec following food on the random-time schedule. But on the fixed-time schedule, the probability of each behavior steadily increased or decreased across the whole interreinforcement interval. Thus, the factors which Staddon and Simmelhag (1971) and Staddon and Ayres (1975) each proposed to account for temporal patterning do indeed affect patterning, but neither is complete by itself. Millenson, Allen, and Pinker (1977) reached a similar conclusion from their work on adjunctive drinking in rats. The effects of postfood time and probability of reinforcement can also be seen by following the analysis proposed by Killeen (1975). Killeen proposes that the temporal patterning of behavior between reinforcement presentations can be described by R = A(e-t/c - e-t/I). I is a measure of the postfood inhibition of responding, which Killeen suggests may be due to a low probability of food following a food presentation. C is a measure of responding at the end of the interval, perhaps controlled by competing responses. By comparing the I and C parameters needed to fit the present data for FT and RT schedules, one can further assess the effects of reinforcement probability on responding. For all types of behavior except RI, the value of I needed to fit the curves on FT and RT schedules (Fig. 2) was the same. (R4: .25; R5: .15; R6: .19; R9: .08). The value of C needed to fit curves for FT and RT differed greatly (R4: .4, 2; R5: .33, 50; R6: .2, 50; R7: 1.4, 50 for FT and RT, respectively). The constancy of I indicates that responding early in the interval is a function of postfood time, not the probability of food. The
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variability of C indicates that responding late in the interval is a function of the probability of reinforcement. For RI, however, different values of both I and C were needed to fit the FT and RT curves (FT: l= 5, C = 6; RT: I= 0, C = 10). One interpretation of this is that RI may be affected by reinforcement probability at all postfood times. This analysis thus confirms the more informal analysis above in indicating that responding just after food is usually controlled by postfood time, and responding later in the interval is controlled by the probability of food. Thus, the present experiments are consistent with Staddon and Simmelhag's proposal that the momentary probability of reinforcement affects the temporal patterning of behavior. However, it was also found that postfood time affects the temporal patterning of behavior. Additionally, response-reinforcer and stimulusreinforcer contingencies affect the frequency of responses, including the pecking of pigeons. Although the present findings are at variance with Staddon and Simmelhag's suggestion that reinforcement contingencies may not affect the frequency of a pigeon's pecking, it is consistent with their more general view that principles of variation may account for the production of behavior, and a selective effect of reinforcement may affect the frequency of behavior. REFERENCES Anderson, M. C., & Shettleworth, S. J. Behavioral adaptation to fixed-interval and fixed-time food delivery in golden hamsters. Journal of the Experimental Analysis of Behavior, 1977, 27, 33-49. Blanchard, R., & Honig, W. K. Surprise value of food detennines its effectiveness as a reinforcer. Journal of Experimental Psychology: Animal Behavior Processes, 1976, 2, 67-74. Brown, P. L., & Jenkins, H. M. Auto-shaping of the pigeon's key-peck. Journal of the Experimental Analysis of Behavior, 1968, 11, 1-8. Fenner, D. H. Key pecking in pigeons maintained by short-interval adventitious schedules of reinforcement. Proceedings of the 77th Annual Convention of the American Psychological Association, 1969, 4, 831832.
Gamzu, E., & Williams, D. R. Classical conditioning of a complex skeletal response. Science, 1971, 171, 923-
925. Herrnstein, R. J. Superstition: A corollary of the principals of operant behavior. In W. K. Honig (Ed.) Operant behavior: Areas of research and application. New York: Appleton-Century-Crofts, 1966. Killeen, P. On the temporal control of behavior. Psychological Review, 1975, 82, 89-115. Kirk, R. Experimental design: Procedures for the behavioral sciences. Belmont, Calif.: Wadsworth, 1968. Lowe, C. F., & Harzem, P. Species differences in temporal control of behavior. Journal of the Experimental Analysis of Behavior, 1977, 28, 189-201. Miller, J. W., & Miller, L. S. Synopsis of the behavior traits of the ring dove. Animal Behavior, 1958, 5, 3-8. Millenson, J. R., Allen, R. B., & Pinker, S. Adjunctive drinking during variable and random-interval food reinforcement schedules. Animal Learning and Behavior, 1977, 5, 285-290. Neuringer, A. J. Superstitious key pecking after three peck-produced reinforcements. Journal of the Experimental Analysis of Behavior, 1970, 13, 127-134. Perkins, C. C., Beavers, W. C., Hancock, R. A., Hemmendinger, P. C., Hemmindinger, D., & Ricci, J. A. Some variables affecting rate of key pecking during response-independent procedures (autoshaping). Journal of the Experimental Analysis of Behavior, 1975, 24, 59-72. Reberg, D., Innis, N. K., Mann, B., & Eizenga, C. 'Superstitious' behaviour resulting from periodic response-independent presentations of food or water. Animal Behavior, 1978, 26, 507-519. Schoenfeld, W. N., Cole, B. K., Lang, J., & Mankoff, B. "Contingency" in behavior theory. In F. J. McGuigan & D. B. Lumsden (Eds.), Contemporary approaches to conditioning and learning. Washington, D.C.: W. H. Winston and Sons, 1973. Staddon, J. E. R., & Ayres, S. L. Sequential and temporal properties of behavior induced by a schedule of periodic food delivery. Behaviour, 1975, 54, 26-49Staddon, J. E. R., & Simmelhag, V. L. The "superstition" experiment: A reexamination of its implications for the principles of adaptive behavior. Psychological Review, 1971, 78, 3-43. Williams, D. R., & Williams, H. Auto-maintenance in the pigeon: Sustained pecking despite contingent non-reinforcement. Journal of the Experimental Analysis of Behavior, 1969, 12, 511-520. Zeiler, M. D. Fixed and variable schedules of responseindependent reinforcement. Journal of the Experimental Analysis of Behavior, 1968, 11, 405-414.
Received September 6, 1979 Final acceptance January 21, 1980
