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Within-Session Changes in Adjunctive and Instrumental Responding
LEARNING AND MOTIVATION ARTICLE NO.
27, 408–427 (1996)
0024
Within-Session Changes in Adjunctive and Instrumental Responding FRANCES K. MCSWEENEY, SAMANTHA SWINDELL, JEFFREY N. WEATHERLY
AND
Washington State University, Pullman Rats pressed levers for food delivered by several fixed interval schedules. A drinking spout or running wheel was also available during some conditions, but not during others. The rate of lever pressing, drinking and running often changed within experimental sessions. The within-session patterns of lever pressing did not differ when drinking or running was available and when it was not. The correlation between the amount of lever pressing and the amount of drinking or running at a particular time in the session was inconsistently positive or negative. Finding within-session changes in responding for adjunctive behaviors implies that the factors that produce these changes are present for both adjunctive and instrumental behavior. Finding inconsistent correlations between instrumental responding and adjunctive behaviors questions arousal and interference from adjunctive behaviors as explanations for within-session changes in instrumental responding. q 1996 Academic Press, Inc.
Responding often increases to a peak and then decreases within sessions when subjects respond on standard operant conditioning procedures (e.g., McSweeney & Hinson, 1992). In the past, within-session changes in responding have been treated as problems to be controlled by procedures such as giving ‘‘warm-up’’ trials (e.g., Hodos & Bonbright, 1972) or time to adapt to the apparatus (e.g., Papini & Overmier, 1985). However, further consideration suggests that these changes may be worthy of study in their own right. Within-session changes may be large and orderly, appearing for individual subjects responding during individual sessions (e.g., McSweeney & Hinson, 1992). They occur for a wide variety of species, procedures, responses, and reinforcers (e.g., McSweeney & Roll, 1993). Finally, they may have a number of important theoretical and methodological implications (e.g., McSweeney & Roll, 1993). For example, within-session changes challenge
This material is based on work supported by the National Science Foundation under Grant IBN-9207346. Some of these results were presented at the 1995 meeting of the Association for Behavior Analysis in Washington, DC. Address reprint requests to Frances K. McSweeney, Department of Psychology, Washington State University, Pullman, WA 99164-4820. 408 0023-9690/96 $18.00 Copyright q 1996 by Academic Press, Inc. All rights of reproduction in any form reserved.
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both molar (e.g., Herrnstein, 1970) and molecular (e.g., Hinson & Staddon, 1983) theories. Molar theories are challenged because within-session changes imply that the primary dependent variable used by these theories, rate of responding averaged over the session, masks strong regularities in behavior at a more molecular level. Molecular theories are challenged because these theories must account for within-session changes if they are to reach their goal of describing behavior on a moment-by-moment basis. The present experiments examined within-session changes in two adjunctive behaviors (e.g., Falk, 1971), polydipsia (Experiment 1) and wheel running (Experiment 2). Adjunctive behaviors were studied for two reasons. First, observing within-session changes in adjunctive behaviors would extend the generality of those changes to behaviors that are not strictly operant. Extending the generality of within-session changes is important. If these changes occur only under limited conditions, then they would reflect processes peculiar to those conditions. If within-session changes occur more generally, then they may reflect processes that are more generally important. Extending the generality to non-operant behaviors is particularly important because it might suggest that the factors that produce within-session changes are sufficiently general that they affect many types of behavior, not just operant responding. Second, examining adjunctive behaviors may help to test two potential explanations for within-session changes in instrumental responding. First, within-session changes have been attributed to changes in arousal within the session (e.g., Killeen, 1994). Although arousal may be defined in many ways, it is often considered to be a state of the animal that determines the ‘‘energy’’ level of its behavior (e.g., Duffy, 1962). If within-session changes in both instrumental and adjunctive behaviors are produced by changes in the same state of arousal, then the rates of operant and adjunctive responding should be positively correlated over the course of the session. In contrast, if interfering responses produce within-session changes in instrumental responding (e.g., Bindra, 1959), within-session changes in adjunctive and instrumental responding might be negatively correlated. Interfering response theories attribute the within-session changes in instrumental responding to changes in unobserved behaviors that interfere with instrumental responding. For example, subjects might explore the chamber early in the session (e.g., Bindra, 1959) and fall asleep later (e.g., Pavlov, 1928). Adjunctive behaviors provide one possible type of interfering response. If withinsession changes in instrumental responding are produced by changes in interfering adjunctive behaviors, then the rates of instrumental and adjunctive responding should be negatively correlated within the session. Within-session changes in instrumental responding should also be larger during schedules that produce more adjunctive behavior. More interference should occur when adjunctive behaviors are more frequent. Therefore, the within-session changes in responding should be larger when more adjunctive behaviors are present than when fewer are present.
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In the present Experiments, rats pressed a lever for food delivered by a fixed interval (FI) 15-, 30-, 60-, 120-, or 240-s schedule in different conditions. Several different FI values were used to generate different amounts of adjunctive behaviors (e.g., Falk, 1971). In Experiment 1, responding on these schedules was studied when a drinking spout was available throughout the session and when it was not. In Experiment 2, responding was studied when access to a running wheel was available throughout the session and when it was not. The experiments studied both licking and wheel running because Staddon (1977) argued that these behaviors may have different properties. In particular, drinking may be an interim behavior while wheel running is a facultative behavior. Interim behaviors occur at a higher rate during a schedule of reinforcement than during appropriate baselines and they usually occur immediately after reinforcement. Facultative behaviors do not occur at a higher rate during a schedule of reinforcement than during appropriate baselines and they occur later in the interreinforcer interval than interim behaviors. In each experiment, the apparatus was arranged so that drinking or running would interfere with instrumental responding. Because of the physical distance between the lever and the drinking spout or running wheel, the subjects could not perform the adjunctive behavior and the instrumental response at the same time. EXPERIMENT 1
Method Subjects. The subjects were 10 experimentally naive male rats bred from Sprague–Dawley stock. They were approximately 120 days old at the start of the experiment. They were housed individually and had free access to water in their home cages. Subjects were maintained at approximately 85% of their free-feeding body weights by postsession feedings delivered when all subjects had completed their session for the day. Subjects were exposed to a 12 h/12 h light/dark cycle. Apparatus. The apparatus measured 20.5 1 19.5 1 23.5 cm. Two 5- 1 1cm levers extended 1.5 cm into the chamber. They were located 10 cm from the ceiling and 1.5 cm from each side of the apparatus. The levers were connected to microswitches which required a force of approximately 45 g to operate. Two 1-cm diameter lights were located above each lever, 3.5 cm below the ceiling. One light was 1.5 cm from the side wall; the other was 3 cm medial to the first. The lights over the left lever were white; those over the right lever were red. The houselight consisted of two 1-cm diameter clear lights located in the ceiling near the back wall. Access to food was through a 4.5-cm square hole, centered between the sides and 1 cm from the floor. The licking spout, which was connected to a lickometer, was available through a 1.8-cm opening on the wall opposite the logic panel. The hole was located 2.5 cm above the floor, 10.2 cm and 9.5 cm from the left and right walls, respectively. The spout was positioned so that it was flush with the wall.
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The experimental enclosure was housed in a sound-attenuating chamber. A ventilating fan masked noises from outside the chamber. Experimental events were programmed, and data were recorded by an IBM-compatible 486 computer running MED-State software. Procedure. Subjects were trained to press the left lever by a shaping by successive approximations procedure. The rate of reinforcement was gradually reduced until subjects responded on a FI 30-s schedule. Then, subjects responded on the following schedules, presented in the following order: FI 30s, FI 120-s, FI 240-s, FI 15-s, and FI 60-s. In all cases, pressing the left lever produced reinforcers (one 45-mg Noyes pellet) and the light over the left lever and the houselight were illuminated throughout the session. For five of the subjects, water was freely available from the drinking spout. For the other five subjects, no water was available. One of the subjects in the water-available condition (subject 111) died before completion of the experiment. Its data were omitted from all analysis. Subject 104 in the water-unavailable condition also died after the 22nd session of the last schedule. The data for that subject have been averaged over five preceding sessions for that, FI 60-s, schedule. Sessions lasted for 60 min and were conducted daily, five to six times per week. Each schedule was presented for 30 sessions. Results and Discussion Table 1 presents the mean rates of responding (responses per minute) for lever pressing and licking averaged over the session. Results are presented for individual subjects and for the mean of all subjects. Rates were calculated by dividing the number of presses or licks during the session by the 60-min session duration. These results, and all of those presented in this paper, were averaged over the last five sessions for which each schedule was available. The rates of both lever pressing and licking were usually higher for schedules that provided higher rates of reinforcement than for those that provided lower rates. One-way (schedule) repeated-measures analyses of variance (ANOVAs) showed that pressing changed significantly with changes in the schedule of reinforcement for both the water-available (F(4,12) Å 10.087, p õ .001) and the water-unavailable (F(4,16) Å 8.632, p õ .001) conditions. The changes in licking approached, but did not reach, significance (F(4,12) Å 2.870, p õ .070). Decreases in rates of lever pressing with increases in FI value are consistent with results reported in many past studies (e.g., Lowe, Harzem, & Spencer, 1979). Figure 1 presents the percentage of total-session lever presses during successive 5-min intervals in the session for the water-available (solid line) and water-unavailable (dashed line) conditions. Percentages were calculated by dividing the number of presses during each 5-min interval by the total number of presses during the session and multiplying by 100. Each graph presents the results for the mean of all subjects responding on a single schedule. Percentages have been presented instead of absolute response rates so that differences in the absolute rates of responding would not obscure similarities
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TABLE 1 Rates of Lever Pressing and Licking (Responses per Minute) for Each Subject Responding during the Last Five Sessions of Each FI Schedule in Experiment 1 Schedule Subject
15-s
30-s
60-s
120-s
240-s
3.8 47.9 2.4 4.8 4.2 11.8 5.2 13.5 3.9 19.5
2.2 15.3 1.0 4.2 1.7 7.7 2.0 8.5 1.7 8.9
1.6 5.0 4.1 0.7 2.3 2.7
1.1 1.0 1.4 0.5 1.5 1.1
Water-available condition 112 113 114 115 Mean
Lever Lick Lever Lick Lever Lick Lever Lick Lever Lick
19.3 57.1 12.3 15.6 7.1 12.1 16.0 11.8 13.7 24.2
15.0 70.2 4.9 15.2 12.3 6.6 14.6 35.1 11.7 31.8
20.0 68.3 12.5 10.1 4.3 13.2 17.8 22.3 13.6 28.5
Water-unavailable conditon 101 102 103 104 105 Mean
Lever Lever Lever Lever Lever Lever
7.7 21.3 20.9 1.8 8.9 12.1
8.1 11.0 12.6 1.9 5.8 7.9
3.6 3.6 6.9 1.0 2.9 3.6
in the within-session changes in responding. All percentages can be converted to absolute response rates by using the absolute rates of responding averaged over the session that are presented in Tables 1 or 3. Figure 1 shows that the rate of lever pressing changed within sessions. Responding primarily decreased within the session for the FI 15-s schedule. Responding increased early in the session and then remained relatively constant or decreased during the other schedules. Although responding was more variable when water was absent than when it was present, the basic form of the within-session changes in responding were similar during these two conditions. Table 2 supports these conclusions. It contains the results of two-way (condition by 5-min interval) mixed-model ANOVAs applied to the rates of pressing during each schedule of reinforcement. ANOVAs were applied to absolute response rates, rather than to the percentages plotted in Fig. 1, because percentages are bounded and cannot be assumed to be normally distributed. The main effect of time was significant for each schedule, indicating that rate of pressing changed significantly within sessions for each schedule. The interaction between time and condition was not significant for any sched-
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FIG. 1. Percentage of total-session lever presses during successive 5-min intervals in the wateravailable (solid line) and water-unavailable (dashed line) conditions in Experiment 1. Each graph presents the results for a single fixed interval schedule. Results are those for the mean of all subjects, averaged over the last five sessions for which the schedule was available.
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TABLE 2 Results of Two-Way (Condition by 5-Min Interval) Mixed-Model Analyses of Variance Applied to the Rates of Lever Pressing during the Water-Available and Water-Unavailable Conditions in Experiment 1 Source
df
F
põ
0.096 4.059 0.341
0.765 0.001 0.974
1.654 2.352 0.741
0.239 0.015 0.696
9.507 3.607 1.577
0.018 0.001 0.123
1.279 3.841 1.028
0.295 0.001 0.431
3.617 3.362 1.741
0.099 0.001 0.080
FI 15-s Condition (C) Time (T) C1T
1, 7 11, 77 11, 77 FI 30-s
Condition (C) Time (T) C1T
1, 7 11, 77 11, 77 FI 60-s
Condition (C) Time (T) C1T
1, 7 11, 77 11, 77 FI 120-s
Condition (C) Time (T) C1T
1, 7 11, 77 11, 77 FI 240-s
Condition (C) Time (T) C1T
1, 7 11, 77 11, 77
ule, indicating that the within-session patterns of pressing did not differ when water was available and when it was not. The within-session changes in lever pressing were not larger for schedules that supported higher rates of licking than for those that supported lower rates. Table 1 shows that the rates of licking were higher during the FI 15-, 30-, and 60-s schedules than during the FI 120- and 240-s schedules. When the highest percentage of total-session lever presses in a water-available schedule (solid line in Fig. 1) was divided by the lowest percentage reported for that schedule, the ratio was 1.47, 1.26, 1.45, 1.66, and 2.89 for the FI 15s, FI 30-s, FI 60-s, FI 120-s and FI 240-s schedules, respectively. Therefore, if anything, the within-session changes in lever pressing were larger for the schedules that produced less (FI 120- or FI 240-s), rather than more (FI 15-, FI 30-, or FI 60-s), licking.
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Figure 2 presents the percentage of total-session responses for pressing (solid line) and licking (dashed line) during successive 5-min intervals in the session for the mean of all subjects responding in the water-available conditions. Each graph presents the results for an FI schedule. Percentages were calculated as in Fig. 1. Figure 2 shows that the rate of licking sometimes changed within sessions. One-way (5-min interval) within-subject ANOVAs applied to the rates of licking confirmed this impression. Licking changed significantly within the session for the FI 30-s (F(11,33) Å 2.113, p õ .048) and FI 240-s (F(11,33) Å 2.806, p õ .011) schedules, but not for the FI 15-s (F(11,33) Å 1.155, p õ .354) or FI 60-s (F(11,33) Å 0.301, p õ .981) schedules. The changes approached significance for the FI 120-s schedule (F(11,33) Å 1.997, p õ .062). Licking increased and then decreased within the session for the FI 30s schedule. It primarily decreased within the session during the FI 240-s schedule. Although Fig. 2 shows that the within-session changes in licking and lever pressing were similar for some schedules (e.g., the FI 15- and FI 60-s), the forms of these changes differed substantially when licking changed significantly within the session. For example, the rate of licking primarily decreased for the FI 240-s schedule. The rate of lever pressing increased and then decreased. These apparent differences were supported by Pearson correlation coefficients, calculated for the rates of pressing and licking during successive 5-min intervals in the session for the water-available conditions. These coefficients are reported in Table 3 for individual subjects and for the mean of all subjects responding on each schedule. Table 3 shows that the correlation between licking and pressing was sometimes positive and sometimes negative. For the two schedules for which licking and pressing both changed significantly (FI 30-s and FI 240-s), one coefficient for the mean was positive and the other was negative. Seven of the eight coefficients for individual subjects were negative, but several of these coefficients were close to 0, indicating that there was little relation between the rate of licking and the rate of pressing. EXPERIMENT 2
Method Subjects. The subjects were 10 experimentally naive male rats bred from Sprague – Dawley stock. They were housed and maintained as in Experiment 1. Apparatus and procedure. The apparatus was a two-lever operant conditioning unit for rats, measuring 21.5 1 20.5 by 28 cm. A 5.5-cm diameter hole that allowed access to Noyes pellets was centered in the logic panel, 1.5 cm above the floor. The two levers were 5 cm wide and extended 2.5 cm into the chamber. Each of them was located 1.5 cm from one side of the apparatus and 7.5 cm above the floor. A 2-cm diameter white light was centered 5 cm above each of the levers. A 2-cm diameter green light that
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FIG. 2. Percentage of total-session responses for pressing (solid line) and licking (dashed line) during successive 5-min intervals in the session during the water-available conditions in Experiment 1. Each graph presents the results for a single fixed interval schedule. Results are those for the mean of all subjects, averaged over the last five sessions for which the schedule was available.
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TABLE 3 Pearson Correlation Coefficients Calculated over the Rate of Lever Pressing and Licking during Successive 5-Min Intervals in the Session during the Water-Available Conditions in Experiment 1 Schedule Subject
15-s
30-s
60-s
120-s
240-s
112 113 114 115 Mean
0.369 00.079 00.682 0.648 0.366
00.110 0.375 00.092 00.165 0.199
00.400 0.262 00.539 0.574 0.482
00.612 0.326 0.374 0.049 0.074
00.542 00.128 00.078 00.073 00.276
served as a houselight was centered in the logic panel 2.5 cm below the ceiling. A 12.7 1 8.3 cm door that allowed access to a Lafayette running wheel appeared on the left wall of the chamber, 10 cm from the logic panel. The wheel was 10.2 cm wide and approximately 35.6 cm in diameter. A 5.7cm ramp provided access to the wheel. A response was counted whenever a spoke of the wheel passed a contact point. Because the wheel had 14 spokes, each response represented turning the wheel by approximately 26 degrees. The experimental enclosure was housed in a sound-attenuating chamber. A ventilating fan masked noises from outside the chamber. Experimental events were programmed, and data were recorded by an IBM-compatible 486 computer running MED-State software. The procedure was identical to that used in Experiment 1 except that five of the subjects had free access to the running wheel, instead of to the drinking spout, throughout the session. One of the rats in the wheel-available condition (Subject 72) died before it completed the experiment. Results are reported for only four subjects for this condition. Results and Discussion Table 4 presents the rates of lever pressing and wheel turning (responses per minute) averaged over the session for each subject responding on each FI schedule when the wheel was available and when it was not. Rates were calculated as in Table 1. Table 4 shows that the rates of lever pressing and wheel turning were usually higher for schedules that provided higher rates of reinforcement than for those that provided lower rates. One-way (schedule) within-subject ANOVAs confirmed that the rates of lever pressing (F(4,12) Å 19.206, p õ .001, wheel-available; F(4,16) Å 3.807, p õ .023, wheelunavailable) and wheel turning (F(4,12) Å 4.265, p õ .022) both changed significantly with changes in the schedule. Figure 3 presents the percentage of the total-session lever presses during the wheel-available (solid line) and the wheel-unavailable conditions (dashed line) during successive 5-min intervals in the session. Each graph presents
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TABLE 4 Rates of Lever Pressing and Wheel Turning (Responses per Minute) for Each Subject Responding during the Last Five Sessions of Each FI Schedule in Experiment 2 Schedule Subject
15-s
30-s
60-s
120-s
240-s
4.5 13.5 6.6 16.4 7.2 13.8 4.9 7.6 5.8 12.8
2.1 4.8 4.6 6.7 2.5 10.6 3.9 1.1 3.3 5.8
1.0 1.3 1.1 11.8 1.2 13.2 2.3 3.4 1.4 7.4
3.9 2.6 3.8 2.4 3.6 3.3
1.8 2.9 2.4 1.5 2.2 2.2
Wheel-available condition 71 73 74 75 Mean
Lever Wheel Lever Wheel Lever Wheel Lever Wheel Lever Wheel
5.3 3.8 5.5 13.1 7.3 16.5 7.6 4.7 6.4 9.5
4.6 6.3 6.9 21.9 4.8 26.4 6.3 5.0 5.7 14.9
Wheel-unavailable condition 171 172 173 174 175 Mean
Lever Lever Lever Lever Lever Lever
8.3 6.5 6.6 6.1 7.9 7.1
13.9 7.7 7.4 7.7 8.8 9.1
5.1 4.0 5.3 19.6 4.6 7.7
the results for the mean of all subjects responding on a different schedule. Percentages were calculated as in Fig. 1. Figure 3 shows that the rate of lever pressing sometimes changed within sessions. Except for the FI 15-s schedule, the within-session changes in pressing were also usually similar regardless of whether the wheel was available or not. These conclusions were confirmed by two-way (condition by 5-min interval) mixed-model ANOVAs applied to the rates of lever pressing. The results of these ANOVAs are presented in Table 5. The interaction between condition and time was not significant for any schedule except the FI 15-s, indicating that the within-session patterns of responding did not differ reliably regardless of whether the wheel was present or absent for most schedules. The main effect of time was significant for the FI 15-s and the FI 120-s schedules, indicating that the rate of lever-pressing changed significantly within sessions for those schedules. Responding primarily increased and then decreased within the session during the FI 120-s schedule and during the FI 15-s schedule when the wheel was present. It decreased within the session during the FI 15-s schedule when the wheel was absent. The within-session changes in responding also approached significance for the FI 30-s schedule (p õ .062). One-way (5-min interval) within-subject ANOVAs applied to the
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FIG. 3. Percentage of the total-session lever presses during successive 5-min intervals in the session in the wheel-available (solid line) and the wheel-unavailable (dashed line) conditions in Experiment 2. Each graph presents the results for a single fixed interval schedule. Results are those for the mean of all subjects, averaged over the last five sessions for which the schedule was available.
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TABLE 5 Results of Two-Way (Condition by 5-Min Interval) Mixed-Model Analyses of Variance Applied to the Rates of Lever Pressing during the Wheel-Available and Wheel-Unavailable Conditions in Experiment 2 Source
df
F
põ
0.824 3.702 4.109
0.394 0.001 0.001
5.441 1.833 1.148
0.052 0.062 0.337
0.319 1.603 0.854
0.590 0.115 0.588
0.000 2.400 1.073
0.984 0.013 0.394
4.020 1.331 0.603
0.085 0.224 0.820
FI 15-s Condition (C) Time (T) C1T
1, 7 11, 77 11, 77 FI 30-s
Condition (C) Time (T) C1T
1, 7 11, 77 11, 77 FI 60-s
Condition (C) Time (T) C1T
1, 7 11, 77 11, 77 FI 120-s
Condition (C) Time (T) C1T
1, 7 11, 77 11, 77 FI 240-s
Condition (C) Time (T) C1T
1, 7 11, 77 11, 77
rates of pressing showed that pressing changed significantly within the session during FI 30-s schedule in the wheel-available (F(11,33) Å 2.205, p õ .039), but not during the wheel-unavailable condition (F(11,44) Å 0.575, p õ .838). Responding increased and then decreased within the session during the wheelavailable condition. The within-session changes in lever pressing during the wheel-available conditions were not larger during the FI schedules that produced more wheel turning than during the schedules that produced less wheel turning. Table 4 shows that the mean rate of wheel-turning was higher during the FI 15-s, FI 30-s and FI 60-s schedules than during the FI 120-s and FI 240-s schedules. When the largest percentage of total-session lever presses in a 5-min interval was divided by the smallest percentage for a wheel-available schedule, the ratio was 1.43, 1.69, 1.19, 2.65 and 2.10 for the FI 15-s, FI 30-s, FI 60-s, FI
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120-s, and FI 240-s schedules, respectively. If anything, within-session changes in operant responding were, on the average, larger for schedules that supported less adjunctive wheel turning (FI 120- or FI 240-s) than for those that supported more adjunctive wheel turning (FI 15-, FI 30-, or FI 60-s). Figure 4 presents the percentage of total-session lever presses (solid line) and wheel turns (dashed line) during successive 5-min intervals for the mean of all subjects responding on each FI schedule during the wheel-available conditions. Results have been calculated and presented as for Fig. 1. Figure 4 shows that the rate of wheel turning usually changed within sessions. Oneway (5-min interval) within-subject ANOVAs applied to the rates of wheel turning were significant for the FI 15-s (F(11,33) Å 5.400, p õ .001), FI 30s (F(11,33) Å 5.694, p õ .001), FI 60-s (F(11,33) Å 2.195, p õ .040) and FI 120-s (F(11,33) Å 2.207, p õ .039) schedules, but not for the FI 240-s (F(11,33) Å 0.775, p õ .662) schedule. Wheel turning increased and then decreased during the session for most schedules. Responding primarily decreased within the session during the FI 60-s schedule. Figure 4 shows that responding usually changed differently within the session for lever pressing and wheel turning, particularly for the schedules for which the changes in both behaviors were statistically significant (FI 15-, FI 30-, and FI 120-s). Table 6 presents Pearson correlation coefficients calculated on the rates of lever pressing and wheel turning during successive 5min intervals in the session for individual subjects and for the mean of all subjects. Table 6 shows that the correlation between the rate of pressing and turning was positive for the mean of all subjects during the FI 15-, FI 30-, and FI 120-s schedules. However, the correlation was close to zero for the FI 15-s schedule. Five of the 12 coefficients were negative and 7 were positive, when the results for individual subjects were examined. GENERAL DISCUSSION
The present experiments showed that the rate of adjunctive licking and wheel turning often changed significantly within experimental sessions. Rate of wheel turning changed significantly for all schedules except the FI 240-s. Rate of licking changed significantly for the FI 30-s and FI 240-s schedules. The changes were marginally significant for the FI 120-s schedule (p õ .062). Extending the generality of within-session changes to non-operant behaviors is important because it suggests that the factors that produce those changes are also present for behaviors that are not strictly operant. In support of this idea, within-session changes have also been observed for classically conditioned responding (e.g., Siegel & Domjan, 1971), consummatory responding (e.g., Rachlin & Krasnoff, 1983), responses that are evoked by stimuli (e.g., habituation, Thompson & Spencer, 1966), ‘‘spontaneously’’ occuring behaviors (e.g., activity, locomotion, exploration, e.g., Montgomery, 1953), and lever pressing before conditioning begins (e.g., Schoenfeld, Antonitis & Bersh, 1950). Therefore, within-session changes in responding may be
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FIG. 4. Percentage of the total-session responses for pressing (circles) and wheel running (triangles) during successive 5-min intervals in the session during the wheel-available conditions in Experiment 2. Each graph presents the results for a single fixed interval schedule. Results are those for the mean of all subjects, averaged over the last five sessions for which the schedule was available.
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TABLE 6 Pearson Correlation Coefficients Calculated over the Rate of Lever Pressing and Wheel Turning during Successive 5-Min Intervals in the Session in the Wheel-Available Conditions in Experiment 2 Schedule Subject
15-s
30-s
60-s
120-s
240-s
71 73 74 75 Mean
0.585 00.621 00.032 00.277 0.079
0.703 0.162 00.364 0.660 0.495
00.495 0.243 0.093 0.389 0.138
0.841 0.408 00.048 0.906 0.668
0.304 0.100 0.311 0.274 0.500
produced by variables that are general enough to occur during all of these different procedures. The present experiments indicate that within-session changes in instrumental responding are probably not produced by one interpretation of withinsession changes in arousal. As argued earlier, arousal is often considered to be a state of the animal that determines the energy level of its behavior (e.g., Duffy, 1962). If within-session changes in adjunctive and instrumental responding are both produced by changes in this single state, then the correlation between these two behaviors should be strongly positive. Tables 3 and 6 indicate that this was not the case. The within-session correlations between the two types of behaviors were sometimes small or negative. They were not always large and positive as would be expected if the changes were produced by changes in arousal. The present results could be reconciled with the concept of arousal by assuming that there is more than one type of arousal. Then, within-session changes in adjunctive behaviors could be attributed to changes in one type and within-session changes in instrumental responding could be attributed to changes in another type. Unfortunately, postulating more than one state of arousal makes the concept less testable. A large number of experimental outcomes could be reconciled with changes in several states of arousal. Therefore, arousal is either an incorrect or a relatively untestable explanation for the present results. The present results question one interpretation of an interfering response explanation for within-session changes in instrumental responding. The present experiments produced two types of behavior, licking and wheel running, that should have interfered with instrumental responding. They also showed that the rate of these potentially interfering responses often changed within experimental sessions. However, several aspects of the data failed to support the idea that changes in these potentially interfering responses contributed to the within-session changes in instrumental responding. First, the correlations between the amounts of adjunctive and instrumental responding were not
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always large and negative as predicted by interfering response theory. Instead, Tables 3 and 6 showed that the correlations were sometimes weak and the sign of the correlations was inconsistently positive or negative. Second, the within-session changes in instrumental responding were not larger when more adjunctive behaviors were present than when fewer or none of those behaviors were present. The interaction terms in Tables 2 and 5 indicated that the forms of the within-session patterns of instrumental responding rarely differed when adjunctive behaviors were present and when they were not. Figures 1 and 3 also showed that the within-session changes in instrumental responding were not larger for schedules that supported more adjunctive behaviors than for those that supported fewer. Instead, the within-session changes in lever pressing were somewhat smaller during schedules that supported higher rates of adjunctive behaviors, than they were during schedules that supported lower rates. It might be argued that the present FI schedules do not provide a good test of competing-response explanations. Little instrumental responding occurs immediately after reinforcement during these schedules (e.g., Schneider, 1969). Therefore, adjunctive behaviors that occurred at that time would interfere little with instrumental responding. This is a reasonable argument and it implies that an effect of competing responses might be found under other circumstances (e.g., a different choice of schedules). However, the argument does not change the basic conclusion that competition from adjunctive behaviors is not necessary to produce within-session changes in instrumental responding. Within-session changes in instrumental responding were observed during many of the present FI schedules even though competition between instrumental and adjunctive behaviors did not occur. The present results differ somewhat from those reported by Premack and Putney (1962). In that experiment, rats pressed levers for light reinforcers and they were also allowed to drink. Lever pressing increased and then decreased within the session while drinking decreased and then increased. Premack and Putney also compared their results to the results obtained by Premack and Collier (1962) for light-reinforced lever pressing when subjects were not allowed to drink. In that case, lever pressing only decreased within the session. Conclusions based on a comparison of the results presented by Premack and Putney to those presented by Premack and Collier are somewhat suspect. These conclusions rest on a comparison of results across studies and differences in the forms of the within-session changes in responding across studies may be attributed to other procedural differences between the studies, rather than to the presence or absence of drinking. The negative correlation between pressing and drinking reported by Premack and Putney cannot be dismissed so easily. It is not known why a negative correlation was reported in that study, but not in this one. One possible explanation is that the studies used different reinforcers (light vs food). Premack and Putney also employed an unusual procedure in which
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the light remained illuminated as long as the lever was depressed. These explanations for the differences in results across studies require testing, but the results reported by Premack and Putney do not change the conclusion that within-session changes in instrumental responding may occur even when adjunctive and instrumental responding are not negatively correlated. Therefore, changes in interfering adjunctive behaviors cannot provide a complete explanation for within-session changes in operant responding. Interference from two types of adjunctive behaviors did not produce the within-session changes in instrumental responding in the present experiment. However, other interfering responses might contribute to the changes. For example, within-session changes in instrumental responding might be attributed to changes in exploration of the chamber. Future experiments should test these other potential interfering response explanations. The present results do not compel a particular theoretical explanation for within-session changes in responding, but they are consistent with several theories. For example, within-session changes in responding might be attributed to sensitization followed by habituation (e.g., Groves & Thompson, 1970) to aspects of the experimental situation that are presented repeatedly (e.g., reinforcers) or for prolonged periods (e.g., the experimental enclosure). Habituation is assumed to be a primitive form of learning (e.g., Thorpe, 1966) that might occur under a wide variety of circumstances including operant conditioning and adjunctive behaviors. The exact form taken by sensitizationhabituation also changes from preparation to preparation (e.g., Hinde, 1970). Therefore, the form of sensitization-habituation might differ for operant and adjunctive behaviors. Future experiments should more directly test the implications of this and other alternative explanations for within-session changes in responding. Although within-session changes in operant lever pressing were observed in both Experiments 1 and 2, these changes differed in some ways from the within-session changes in operant responding reported in the past. First, the present changes were relatively small. As argued earlier, the ratio of the highest to the lowest percentage of responding was 1.47, 1.26, 1.45, 1.66, and 2.89 for the FI 15-s, FI 30-s, FI 60-s, FI 120-s, and FI 240-s schedules during the water-available conditions in Experiment 1. The same ratios for the wheel-available conditions in Experiment 2 were 1.43, 1.69, 1.19, 2.65 and 2.10. In contrast, ratios, calculated and reported in the same way, were approximately 7, 5, 1, 1, and 2 for pigeons pecking keys for mixed grain (McSweeney, Roll & Weatherly, 1994). Second, within-session changes in responding are often (e.g., McSweeney, 1992), but not always (e.g., McSweeney, Roll & Cannon, 1994), larger and peak earlier for schedules that provide higher, than for those that provide lower, rates of reinforcement. As just indicated, if anything, the present within-session changes were larger for schedules providing lower rates of reinforcement. The location of the peak response rate also changed erratically with changes in the rate of reinforcement. The peak rate of responding was reached during the second, fifth,
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sixth, fifth, and third 5-min intervals for the FI 15-s, FI 30-s, FI 60-s, FI 120s, and FI 240-s schedules, respectively, during the water-available conditions. The peak rate was reached in the fourth, fourth, third or fifth, second and fourth 5-min interval during the same schedules in the wheel-available conditions. A large number of procedural differences between the studies might account for these differences. Future experiments should directly examine some of these procedural explanations. REFERENCES Bindra, D. (1959). Stimulus change, reactions to novelty and response decrement. Psychological Review, 66, 96–103. Duffy, E. (1962). Activation and behavior. New York: Wiley. Falk, J. L. (1971). The nature and determinants of adjunctive behavior. Physiology & Behavior, 6, 577–588. Groves, P. M., & Thompson, R. F. (1970). Habituation: A dual process theory. Psychological Review, 77, 419–450. Herrnstein, R. J. (1970). On the law of effect. Journal of the Experimental Analysis of Behavior, 13, 243–266. Hinde, R. A. (1970). Behavioral habituation. In G. Horn & R. A. Hinde (Eds.) Short-term changes in neural activity and behavior (pp. 3–40). Cambridge, England: Cambridge Univ. Press. Hinson, J. M., & Staddon, J. E. R. (1983). Hill-climbing by pigeons. Journal of the Experimental Analysis of Behavior, 39, 25–47. Hodos, W., & Bonbright, J. C., Jr. (1972). The detection of visual intensity differences by pigeons. Journal of the Experimental Analysis of Behavior, 18, 471–479. Killeen, P. R. (1994). Mathematical principles of reinforcement. Behavioral and Brain Sciences, 17, 105–172. Lowe, C. F., Harzem, P., & Spencer, P. T. (1979). Temporal control of behavior and the power law. Journal of the Experimental Analysis of Behavior, 31, 333–343. McSweeney, F. K. (1992). Rate of reinforcement and session duration as determinants of withinsession patterns of responding. Animal Learning & Behavior, 20, 160–169. McSweeney, F. K., & Hinson, J. M. (1992). Patterns of responding within sessions. Journal of the Experimental Analysis of Behavior, 58, 19–36. McSweeney, F. K., & Roll, J. M. (1993). Responding changes systematically within sessions during conditioning procedures. Journal of the Experimental Analysis of Behavior, 60, 621– 640. McSweeney, F. K., Roll, J. M., & Cannon, C. B. (1994). The generality of within-session patterns of responding: Rate of reinforcement and session length. Animal Learning & Behavior, 22, 252–266. McSweeney, F. K., Roll, J. M., & Weatherly, J. N. (1994). Within-session changes in responding during several simple schedules. Journal of the Experimental Analysis of Behavior, 62, 109–132. Montgomery, K. C. (1953). The effect of activity deprivation upon exploratory behavior. Journal of Comparative and Physiological Psychology, 46, 438–441. Papini, M. R., & Overmier, J. B. (1985). Partial reinforcement and autoshaping of the pigeon’s key-peck behavior. Learning and Motivation, 16, 109–123. Pavlov, I. P. (1928). Lectures on conditioned reflexes (p. 307). New York: International. Premack, D., & Collier, G. (1962). Analysis of non-reinforcement variables affecting response probability. Psychological Monographs: General and Applied, 76, (5, whole number 524). Premack, D., & Putney, R. T. (1962). Relation between intersession interval, frequency of competing responses and rate of learning. Journal of Experimental Psychology, 63, 269– 274.
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Rachlin, H., & Krasnoff, J. (1983). Eating and drinking: An economic analysis. Journal of the Experimental Analysis of Behavior, 39, 385–404. Schneider, B. A. (1969). A two-state analysis of fixed-interval responding in the pigeon. Journal of the Experimental Analysis of Behavior, 12, 677–687. Schoenfeld, W. N., Antonitis, J. J., & Bersh, P. J. (1950). Unconditioned response rate of the white rat in a barpressing apparatus. Journal of Comparative and Physiological Psychology, 43, 41–48. Siegel, S., & Domjan, M. (1971). Backward conditioning as an inhibitory procedure. Learning and Motivation, 2, 1–11. Staddon, J. E. R. (1977). Schedule-induced behavior. In W. K. Honig & J. E. R. Staddon (Eds.), Handbook of operant behavior (pp. 125–152). Englewood Cliffs, NJ: Prentice Hall. Thompson, R. F., & Spencer, W. A. (1966). Habituation: A model phenomenon for the study of neuronal substrates of behavior. Psychological Review, 73, 16–43. Thorpe, W. H. (1966). Learning and instinct in animals (pp. 55–75). Cambridge, MA: Harvard Univ. Press. Received September 20, 1995 Revised November 8, 1995
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0024
Within-Session Changes in Adjunctive and Instrumental Responding FRANCES K. MCSWEENEY, SAMANTHA SWINDELL, JEFFREY N. WEATHERLY
AND
Washington State University, Pullman Rats pressed levers for food delivered by several fixed interval schedules. A drinking spout or running wheel was also available during some conditions, but not during others. The rate of lever pressing, drinking and running often changed within experimental sessions. The within-session patterns of lever pressing did not differ when drinking or running was available and when it was not. The correlation between the amount of lever pressing and the amount of drinking or running at a particular time in the session was inconsistently positive or negative. Finding within-session changes in responding for adjunctive behaviors implies that the factors that produce these changes are present for both adjunctive and instrumental behavior. Finding inconsistent correlations between instrumental responding and adjunctive behaviors questions arousal and interference from adjunctive behaviors as explanations for within-session changes in instrumental responding. q 1996 Academic Press, Inc.
Responding often increases to a peak and then decreases within sessions when subjects respond on standard operant conditioning procedures (e.g., McSweeney & Hinson, 1992). In the past, within-session changes in responding have been treated as problems to be controlled by procedures such as giving ‘‘warm-up’’ trials (e.g., Hodos & Bonbright, 1972) or time to adapt to the apparatus (e.g., Papini & Overmier, 1985). However, further consideration suggests that these changes may be worthy of study in their own right. Within-session changes may be large and orderly, appearing for individual subjects responding during individual sessions (e.g., McSweeney & Hinson, 1992). They occur for a wide variety of species, procedures, responses, and reinforcers (e.g., McSweeney & Roll, 1993). Finally, they may have a number of important theoretical and methodological implications (e.g., McSweeney & Roll, 1993). For example, within-session changes challenge
This material is based on work supported by the National Science Foundation under Grant IBN-9207346. Some of these results were presented at the 1995 meeting of the Association for Behavior Analysis in Washington, DC. Address reprint requests to Frances K. McSweeney, Department of Psychology, Washington State University, Pullman, WA 99164-4820. 408 0023-9690/96 $18.00 Copyright q 1996 by Academic Press, Inc. All rights of reproduction in any form reserved.
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both molar (e.g., Herrnstein, 1970) and molecular (e.g., Hinson & Staddon, 1983) theories. Molar theories are challenged because within-session changes imply that the primary dependent variable used by these theories, rate of responding averaged over the session, masks strong regularities in behavior at a more molecular level. Molecular theories are challenged because these theories must account for within-session changes if they are to reach their goal of describing behavior on a moment-by-moment basis. The present experiments examined within-session changes in two adjunctive behaviors (e.g., Falk, 1971), polydipsia (Experiment 1) and wheel running (Experiment 2). Adjunctive behaviors were studied for two reasons. First, observing within-session changes in adjunctive behaviors would extend the generality of those changes to behaviors that are not strictly operant. Extending the generality of within-session changes is important. If these changes occur only under limited conditions, then they would reflect processes peculiar to those conditions. If within-session changes occur more generally, then they may reflect processes that are more generally important. Extending the generality to non-operant behaviors is particularly important because it might suggest that the factors that produce within-session changes are sufficiently general that they affect many types of behavior, not just operant responding. Second, examining adjunctive behaviors may help to test two potential explanations for within-session changes in instrumental responding. First, within-session changes have been attributed to changes in arousal within the session (e.g., Killeen, 1994). Although arousal may be defined in many ways, it is often considered to be a state of the animal that determines the ‘‘energy’’ level of its behavior (e.g., Duffy, 1962). If within-session changes in both instrumental and adjunctive behaviors are produced by changes in the same state of arousal, then the rates of operant and adjunctive responding should be positively correlated over the course of the session. In contrast, if interfering responses produce within-session changes in instrumental responding (e.g., Bindra, 1959), within-session changes in adjunctive and instrumental responding might be negatively correlated. Interfering response theories attribute the within-session changes in instrumental responding to changes in unobserved behaviors that interfere with instrumental responding. For example, subjects might explore the chamber early in the session (e.g., Bindra, 1959) and fall asleep later (e.g., Pavlov, 1928). Adjunctive behaviors provide one possible type of interfering response. If withinsession changes in instrumental responding are produced by changes in interfering adjunctive behaviors, then the rates of instrumental and adjunctive responding should be negatively correlated within the session. Within-session changes in instrumental responding should also be larger during schedules that produce more adjunctive behavior. More interference should occur when adjunctive behaviors are more frequent. Therefore, the within-session changes in responding should be larger when more adjunctive behaviors are present than when fewer are present.
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In the present Experiments, rats pressed a lever for food delivered by a fixed interval (FI) 15-, 30-, 60-, 120-, or 240-s schedule in different conditions. Several different FI values were used to generate different amounts of adjunctive behaviors (e.g., Falk, 1971). In Experiment 1, responding on these schedules was studied when a drinking spout was available throughout the session and when it was not. In Experiment 2, responding was studied when access to a running wheel was available throughout the session and when it was not. The experiments studied both licking and wheel running because Staddon (1977) argued that these behaviors may have different properties. In particular, drinking may be an interim behavior while wheel running is a facultative behavior. Interim behaviors occur at a higher rate during a schedule of reinforcement than during appropriate baselines and they usually occur immediately after reinforcement. Facultative behaviors do not occur at a higher rate during a schedule of reinforcement than during appropriate baselines and they occur later in the interreinforcer interval than interim behaviors. In each experiment, the apparatus was arranged so that drinking or running would interfere with instrumental responding. Because of the physical distance between the lever and the drinking spout or running wheel, the subjects could not perform the adjunctive behavior and the instrumental response at the same time. EXPERIMENT 1
Method Subjects. The subjects were 10 experimentally naive male rats bred from Sprague–Dawley stock. They were approximately 120 days old at the start of the experiment. They were housed individually and had free access to water in their home cages. Subjects were maintained at approximately 85% of their free-feeding body weights by postsession feedings delivered when all subjects had completed their session for the day. Subjects were exposed to a 12 h/12 h light/dark cycle. Apparatus. The apparatus measured 20.5 1 19.5 1 23.5 cm. Two 5- 1 1cm levers extended 1.5 cm into the chamber. They were located 10 cm from the ceiling and 1.5 cm from each side of the apparatus. The levers were connected to microswitches which required a force of approximately 45 g to operate. Two 1-cm diameter lights were located above each lever, 3.5 cm below the ceiling. One light was 1.5 cm from the side wall; the other was 3 cm medial to the first. The lights over the left lever were white; those over the right lever were red. The houselight consisted of two 1-cm diameter clear lights located in the ceiling near the back wall. Access to food was through a 4.5-cm square hole, centered between the sides and 1 cm from the floor. The licking spout, which was connected to a lickometer, was available through a 1.8-cm opening on the wall opposite the logic panel. The hole was located 2.5 cm above the floor, 10.2 cm and 9.5 cm from the left and right walls, respectively. The spout was positioned so that it was flush with the wall.
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The experimental enclosure was housed in a sound-attenuating chamber. A ventilating fan masked noises from outside the chamber. Experimental events were programmed, and data were recorded by an IBM-compatible 486 computer running MED-State software. Procedure. Subjects were trained to press the left lever by a shaping by successive approximations procedure. The rate of reinforcement was gradually reduced until subjects responded on a FI 30-s schedule. Then, subjects responded on the following schedules, presented in the following order: FI 30s, FI 120-s, FI 240-s, FI 15-s, and FI 60-s. In all cases, pressing the left lever produced reinforcers (one 45-mg Noyes pellet) and the light over the left lever and the houselight were illuminated throughout the session. For five of the subjects, water was freely available from the drinking spout. For the other five subjects, no water was available. One of the subjects in the water-available condition (subject 111) died before completion of the experiment. Its data were omitted from all analysis. Subject 104 in the water-unavailable condition also died after the 22nd session of the last schedule. The data for that subject have been averaged over five preceding sessions for that, FI 60-s, schedule. Sessions lasted for 60 min and were conducted daily, five to six times per week. Each schedule was presented for 30 sessions. Results and Discussion Table 1 presents the mean rates of responding (responses per minute) for lever pressing and licking averaged over the session. Results are presented for individual subjects and for the mean of all subjects. Rates were calculated by dividing the number of presses or licks during the session by the 60-min session duration. These results, and all of those presented in this paper, were averaged over the last five sessions for which each schedule was available. The rates of both lever pressing and licking were usually higher for schedules that provided higher rates of reinforcement than for those that provided lower rates. One-way (schedule) repeated-measures analyses of variance (ANOVAs) showed that pressing changed significantly with changes in the schedule of reinforcement for both the water-available (F(4,12) Å 10.087, p õ .001) and the water-unavailable (F(4,16) Å 8.632, p õ .001) conditions. The changes in licking approached, but did not reach, significance (F(4,12) Å 2.870, p õ .070). Decreases in rates of lever pressing with increases in FI value are consistent with results reported in many past studies (e.g., Lowe, Harzem, & Spencer, 1979). Figure 1 presents the percentage of total-session lever presses during successive 5-min intervals in the session for the water-available (solid line) and water-unavailable (dashed line) conditions. Percentages were calculated by dividing the number of presses during each 5-min interval by the total number of presses during the session and multiplying by 100. Each graph presents the results for the mean of all subjects responding on a single schedule. Percentages have been presented instead of absolute response rates so that differences in the absolute rates of responding would not obscure similarities
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TABLE 1 Rates of Lever Pressing and Licking (Responses per Minute) for Each Subject Responding during the Last Five Sessions of Each FI Schedule in Experiment 1 Schedule Subject
15-s
30-s
60-s
120-s
240-s
3.8 47.9 2.4 4.8 4.2 11.8 5.2 13.5 3.9 19.5
2.2 15.3 1.0 4.2 1.7 7.7 2.0 8.5 1.7 8.9
1.6 5.0 4.1 0.7 2.3 2.7
1.1 1.0 1.4 0.5 1.5 1.1
Water-available condition 112 113 114 115 Mean
Lever Lick Lever Lick Lever Lick Lever Lick Lever Lick
19.3 57.1 12.3 15.6 7.1 12.1 16.0 11.8 13.7 24.2
15.0 70.2 4.9 15.2 12.3 6.6 14.6 35.1 11.7 31.8
20.0 68.3 12.5 10.1 4.3 13.2 17.8 22.3 13.6 28.5
Water-unavailable conditon 101 102 103 104 105 Mean
Lever Lever Lever Lever Lever Lever
7.7 21.3 20.9 1.8 8.9 12.1
8.1 11.0 12.6 1.9 5.8 7.9
3.6 3.6 6.9 1.0 2.9 3.6
in the within-session changes in responding. All percentages can be converted to absolute response rates by using the absolute rates of responding averaged over the session that are presented in Tables 1 or 3. Figure 1 shows that the rate of lever pressing changed within sessions. Responding primarily decreased within the session for the FI 15-s schedule. Responding increased early in the session and then remained relatively constant or decreased during the other schedules. Although responding was more variable when water was absent than when it was present, the basic form of the within-session changes in responding were similar during these two conditions. Table 2 supports these conclusions. It contains the results of two-way (condition by 5-min interval) mixed-model ANOVAs applied to the rates of pressing during each schedule of reinforcement. ANOVAs were applied to absolute response rates, rather than to the percentages plotted in Fig. 1, because percentages are bounded and cannot be assumed to be normally distributed. The main effect of time was significant for each schedule, indicating that rate of pressing changed significantly within sessions for each schedule. The interaction between time and condition was not significant for any sched-
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FIG. 1. Percentage of total-session lever presses during successive 5-min intervals in the wateravailable (solid line) and water-unavailable (dashed line) conditions in Experiment 1. Each graph presents the results for a single fixed interval schedule. Results are those for the mean of all subjects, averaged over the last five sessions for which the schedule was available.
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TABLE 2 Results of Two-Way (Condition by 5-Min Interval) Mixed-Model Analyses of Variance Applied to the Rates of Lever Pressing during the Water-Available and Water-Unavailable Conditions in Experiment 1 Source
df
F
põ
0.096 4.059 0.341
0.765 0.001 0.974
1.654 2.352 0.741
0.239 0.015 0.696
9.507 3.607 1.577
0.018 0.001 0.123
1.279 3.841 1.028
0.295 0.001 0.431
3.617 3.362 1.741
0.099 0.001 0.080
FI 15-s Condition (C) Time (T) C1T
1, 7 11, 77 11, 77 FI 30-s
Condition (C) Time (T) C1T
1, 7 11, 77 11, 77 FI 60-s
Condition (C) Time (T) C1T
1, 7 11, 77 11, 77 FI 120-s
Condition (C) Time (T) C1T
1, 7 11, 77 11, 77 FI 240-s
Condition (C) Time (T) C1T
1, 7 11, 77 11, 77
ule, indicating that the within-session patterns of pressing did not differ when water was available and when it was not. The within-session changes in lever pressing were not larger for schedules that supported higher rates of licking than for those that supported lower rates. Table 1 shows that the rates of licking were higher during the FI 15-, 30-, and 60-s schedules than during the FI 120- and 240-s schedules. When the highest percentage of total-session lever presses in a water-available schedule (solid line in Fig. 1) was divided by the lowest percentage reported for that schedule, the ratio was 1.47, 1.26, 1.45, 1.66, and 2.89 for the FI 15s, FI 30-s, FI 60-s, FI 120-s and FI 240-s schedules, respectively. Therefore, if anything, the within-session changes in lever pressing were larger for the schedules that produced less (FI 120- or FI 240-s), rather than more (FI 15-, FI 30-, or FI 60-s), licking.
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Figure 2 presents the percentage of total-session responses for pressing (solid line) and licking (dashed line) during successive 5-min intervals in the session for the mean of all subjects responding in the water-available conditions. Each graph presents the results for an FI schedule. Percentages were calculated as in Fig. 1. Figure 2 shows that the rate of licking sometimes changed within sessions. One-way (5-min interval) within-subject ANOVAs applied to the rates of licking confirmed this impression. Licking changed significantly within the session for the FI 30-s (F(11,33) Å 2.113, p õ .048) and FI 240-s (F(11,33) Å 2.806, p õ .011) schedules, but not for the FI 15-s (F(11,33) Å 1.155, p õ .354) or FI 60-s (F(11,33) Å 0.301, p õ .981) schedules. The changes approached significance for the FI 120-s schedule (F(11,33) Å 1.997, p õ .062). Licking increased and then decreased within the session for the FI 30s schedule. It primarily decreased within the session during the FI 240-s schedule. Although Fig. 2 shows that the within-session changes in licking and lever pressing were similar for some schedules (e.g., the FI 15- and FI 60-s), the forms of these changes differed substantially when licking changed significantly within the session. For example, the rate of licking primarily decreased for the FI 240-s schedule. The rate of lever pressing increased and then decreased. These apparent differences were supported by Pearson correlation coefficients, calculated for the rates of pressing and licking during successive 5-min intervals in the session for the water-available conditions. These coefficients are reported in Table 3 for individual subjects and for the mean of all subjects responding on each schedule. Table 3 shows that the correlation between licking and pressing was sometimes positive and sometimes negative. For the two schedules for which licking and pressing both changed significantly (FI 30-s and FI 240-s), one coefficient for the mean was positive and the other was negative. Seven of the eight coefficients for individual subjects were negative, but several of these coefficients were close to 0, indicating that there was little relation between the rate of licking and the rate of pressing. EXPERIMENT 2
Method Subjects. The subjects were 10 experimentally naive male rats bred from Sprague – Dawley stock. They were housed and maintained as in Experiment 1. Apparatus and procedure. The apparatus was a two-lever operant conditioning unit for rats, measuring 21.5 1 20.5 by 28 cm. A 5.5-cm diameter hole that allowed access to Noyes pellets was centered in the logic panel, 1.5 cm above the floor. The two levers were 5 cm wide and extended 2.5 cm into the chamber. Each of them was located 1.5 cm from one side of the apparatus and 7.5 cm above the floor. A 2-cm diameter white light was centered 5 cm above each of the levers. A 2-cm diameter green light that
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FIG. 2. Percentage of total-session responses for pressing (solid line) and licking (dashed line) during successive 5-min intervals in the session during the water-available conditions in Experiment 1. Each graph presents the results for a single fixed interval schedule. Results are those for the mean of all subjects, averaged over the last five sessions for which the schedule was available.
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TABLE 3 Pearson Correlation Coefficients Calculated over the Rate of Lever Pressing and Licking during Successive 5-Min Intervals in the Session during the Water-Available Conditions in Experiment 1 Schedule Subject
15-s
30-s
60-s
120-s
240-s
112 113 114 115 Mean
0.369 00.079 00.682 0.648 0.366
00.110 0.375 00.092 00.165 0.199
00.400 0.262 00.539 0.574 0.482
00.612 0.326 0.374 0.049 0.074
00.542 00.128 00.078 00.073 00.276
served as a houselight was centered in the logic panel 2.5 cm below the ceiling. A 12.7 1 8.3 cm door that allowed access to a Lafayette running wheel appeared on the left wall of the chamber, 10 cm from the logic panel. The wheel was 10.2 cm wide and approximately 35.6 cm in diameter. A 5.7cm ramp provided access to the wheel. A response was counted whenever a spoke of the wheel passed a contact point. Because the wheel had 14 spokes, each response represented turning the wheel by approximately 26 degrees. The experimental enclosure was housed in a sound-attenuating chamber. A ventilating fan masked noises from outside the chamber. Experimental events were programmed, and data were recorded by an IBM-compatible 486 computer running MED-State software. The procedure was identical to that used in Experiment 1 except that five of the subjects had free access to the running wheel, instead of to the drinking spout, throughout the session. One of the rats in the wheel-available condition (Subject 72) died before it completed the experiment. Results are reported for only four subjects for this condition. Results and Discussion Table 4 presents the rates of lever pressing and wheel turning (responses per minute) averaged over the session for each subject responding on each FI schedule when the wheel was available and when it was not. Rates were calculated as in Table 1. Table 4 shows that the rates of lever pressing and wheel turning were usually higher for schedules that provided higher rates of reinforcement than for those that provided lower rates. One-way (schedule) within-subject ANOVAs confirmed that the rates of lever pressing (F(4,12) Å 19.206, p õ .001, wheel-available; F(4,16) Å 3.807, p õ .023, wheelunavailable) and wheel turning (F(4,12) Å 4.265, p õ .022) both changed significantly with changes in the schedule. Figure 3 presents the percentage of the total-session lever presses during the wheel-available (solid line) and the wheel-unavailable conditions (dashed line) during successive 5-min intervals in the session. Each graph presents
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TABLE 4 Rates of Lever Pressing and Wheel Turning (Responses per Minute) for Each Subject Responding during the Last Five Sessions of Each FI Schedule in Experiment 2 Schedule Subject
15-s
30-s
60-s
120-s
240-s
4.5 13.5 6.6 16.4 7.2 13.8 4.9 7.6 5.8 12.8
2.1 4.8 4.6 6.7 2.5 10.6 3.9 1.1 3.3 5.8
1.0 1.3 1.1 11.8 1.2 13.2 2.3 3.4 1.4 7.4
3.9 2.6 3.8 2.4 3.6 3.3
1.8 2.9 2.4 1.5 2.2 2.2
Wheel-available condition 71 73 74 75 Mean
Lever Wheel Lever Wheel Lever Wheel Lever Wheel Lever Wheel
5.3 3.8 5.5 13.1 7.3 16.5 7.6 4.7 6.4 9.5
4.6 6.3 6.9 21.9 4.8 26.4 6.3 5.0 5.7 14.9
Wheel-unavailable condition 171 172 173 174 175 Mean
Lever Lever Lever Lever Lever Lever
8.3 6.5 6.6 6.1 7.9 7.1
13.9 7.7 7.4 7.7 8.8 9.1
5.1 4.0 5.3 19.6 4.6 7.7
the results for the mean of all subjects responding on a different schedule. Percentages were calculated as in Fig. 1. Figure 3 shows that the rate of lever pressing sometimes changed within sessions. Except for the FI 15-s schedule, the within-session changes in pressing were also usually similar regardless of whether the wheel was available or not. These conclusions were confirmed by two-way (condition by 5-min interval) mixed-model ANOVAs applied to the rates of lever pressing. The results of these ANOVAs are presented in Table 5. The interaction between condition and time was not significant for any schedule except the FI 15-s, indicating that the within-session patterns of responding did not differ reliably regardless of whether the wheel was present or absent for most schedules. The main effect of time was significant for the FI 15-s and the FI 120-s schedules, indicating that the rate of lever-pressing changed significantly within sessions for those schedules. Responding primarily increased and then decreased within the session during the FI 120-s schedule and during the FI 15-s schedule when the wheel was present. It decreased within the session during the FI 15-s schedule when the wheel was absent. The within-session changes in responding also approached significance for the FI 30-s schedule (p õ .062). One-way (5-min interval) within-subject ANOVAs applied to the
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FIG. 3. Percentage of the total-session lever presses during successive 5-min intervals in the session in the wheel-available (solid line) and the wheel-unavailable (dashed line) conditions in Experiment 2. Each graph presents the results for a single fixed interval schedule. Results are those for the mean of all subjects, averaged over the last five sessions for which the schedule was available.
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TABLE 5 Results of Two-Way (Condition by 5-Min Interval) Mixed-Model Analyses of Variance Applied to the Rates of Lever Pressing during the Wheel-Available and Wheel-Unavailable Conditions in Experiment 2 Source
df
F
põ
0.824 3.702 4.109
0.394 0.001 0.001
5.441 1.833 1.148
0.052 0.062 0.337
0.319 1.603 0.854
0.590 0.115 0.588
0.000 2.400 1.073
0.984 0.013 0.394
4.020 1.331 0.603
0.085 0.224 0.820
FI 15-s Condition (C) Time (T) C1T
1, 7 11, 77 11, 77 FI 30-s
Condition (C) Time (T) C1T
1, 7 11, 77 11, 77 FI 60-s
Condition (C) Time (T) C1T
1, 7 11, 77 11, 77 FI 120-s
Condition (C) Time (T) C1T
1, 7 11, 77 11, 77 FI 240-s
Condition (C) Time (T) C1T
1, 7 11, 77 11, 77
rates of pressing showed that pressing changed significantly within the session during FI 30-s schedule in the wheel-available (F(11,33) Å 2.205, p õ .039), but not during the wheel-unavailable condition (F(11,44) Å 0.575, p õ .838). Responding increased and then decreased within the session during the wheelavailable condition. The within-session changes in lever pressing during the wheel-available conditions were not larger during the FI schedules that produced more wheel turning than during the schedules that produced less wheel turning. Table 4 shows that the mean rate of wheel-turning was higher during the FI 15-s, FI 30-s and FI 60-s schedules than during the FI 120-s and FI 240-s schedules. When the largest percentage of total-session lever presses in a 5-min interval was divided by the smallest percentage for a wheel-available schedule, the ratio was 1.43, 1.69, 1.19, 2.65 and 2.10 for the FI 15-s, FI 30-s, FI 60-s, FI
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120-s, and FI 240-s schedules, respectively. If anything, within-session changes in operant responding were, on the average, larger for schedules that supported less adjunctive wheel turning (FI 120- or FI 240-s) than for those that supported more adjunctive wheel turning (FI 15-, FI 30-, or FI 60-s). Figure 4 presents the percentage of total-session lever presses (solid line) and wheel turns (dashed line) during successive 5-min intervals for the mean of all subjects responding on each FI schedule during the wheel-available conditions. Results have been calculated and presented as for Fig. 1. Figure 4 shows that the rate of wheel turning usually changed within sessions. Oneway (5-min interval) within-subject ANOVAs applied to the rates of wheel turning were significant for the FI 15-s (F(11,33) Å 5.400, p õ .001), FI 30s (F(11,33) Å 5.694, p õ .001), FI 60-s (F(11,33) Å 2.195, p õ .040) and FI 120-s (F(11,33) Å 2.207, p õ .039) schedules, but not for the FI 240-s (F(11,33) Å 0.775, p õ .662) schedule. Wheel turning increased and then decreased during the session for most schedules. Responding primarily decreased within the session during the FI 60-s schedule. Figure 4 shows that responding usually changed differently within the session for lever pressing and wheel turning, particularly for the schedules for which the changes in both behaviors were statistically significant (FI 15-, FI 30-, and FI 120-s). Table 6 presents Pearson correlation coefficients calculated on the rates of lever pressing and wheel turning during successive 5min intervals in the session for individual subjects and for the mean of all subjects. Table 6 shows that the correlation between the rate of pressing and turning was positive for the mean of all subjects during the FI 15-, FI 30-, and FI 120-s schedules. However, the correlation was close to zero for the FI 15-s schedule. Five of the 12 coefficients were negative and 7 were positive, when the results for individual subjects were examined. GENERAL DISCUSSION
The present experiments showed that the rate of adjunctive licking and wheel turning often changed significantly within experimental sessions. Rate of wheel turning changed significantly for all schedules except the FI 240-s. Rate of licking changed significantly for the FI 30-s and FI 240-s schedules. The changes were marginally significant for the FI 120-s schedule (p õ .062). Extending the generality of within-session changes to non-operant behaviors is important because it suggests that the factors that produce those changes are also present for behaviors that are not strictly operant. In support of this idea, within-session changes have also been observed for classically conditioned responding (e.g., Siegel & Domjan, 1971), consummatory responding (e.g., Rachlin & Krasnoff, 1983), responses that are evoked by stimuli (e.g., habituation, Thompson & Spencer, 1966), ‘‘spontaneously’’ occuring behaviors (e.g., activity, locomotion, exploration, e.g., Montgomery, 1953), and lever pressing before conditioning begins (e.g., Schoenfeld, Antonitis & Bersh, 1950). Therefore, within-session changes in responding may be
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FIG. 4. Percentage of the total-session responses for pressing (circles) and wheel running (triangles) during successive 5-min intervals in the session during the wheel-available conditions in Experiment 2. Each graph presents the results for a single fixed interval schedule. Results are those for the mean of all subjects, averaged over the last five sessions for which the schedule was available.
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TABLE 6 Pearson Correlation Coefficients Calculated over the Rate of Lever Pressing and Wheel Turning during Successive 5-Min Intervals in the Session in the Wheel-Available Conditions in Experiment 2 Schedule Subject
15-s
30-s
60-s
120-s
240-s
71 73 74 75 Mean
0.585 00.621 00.032 00.277 0.079
0.703 0.162 00.364 0.660 0.495
00.495 0.243 0.093 0.389 0.138
0.841 0.408 00.048 0.906 0.668
0.304 0.100 0.311 0.274 0.500
produced by variables that are general enough to occur during all of these different procedures. The present experiments indicate that within-session changes in instrumental responding are probably not produced by one interpretation of withinsession changes in arousal. As argued earlier, arousal is often considered to be a state of the animal that determines the energy level of its behavior (e.g., Duffy, 1962). If within-session changes in adjunctive and instrumental responding are both produced by changes in this single state, then the correlation between these two behaviors should be strongly positive. Tables 3 and 6 indicate that this was not the case. The within-session correlations between the two types of behaviors were sometimes small or negative. They were not always large and positive as would be expected if the changes were produced by changes in arousal. The present results could be reconciled with the concept of arousal by assuming that there is more than one type of arousal. Then, within-session changes in adjunctive behaviors could be attributed to changes in one type and within-session changes in instrumental responding could be attributed to changes in another type. Unfortunately, postulating more than one state of arousal makes the concept less testable. A large number of experimental outcomes could be reconciled with changes in several states of arousal. Therefore, arousal is either an incorrect or a relatively untestable explanation for the present results. The present results question one interpretation of an interfering response explanation for within-session changes in instrumental responding. The present experiments produced two types of behavior, licking and wheel running, that should have interfered with instrumental responding. They also showed that the rate of these potentially interfering responses often changed within experimental sessions. However, several aspects of the data failed to support the idea that changes in these potentially interfering responses contributed to the within-session changes in instrumental responding. First, the correlations between the amounts of adjunctive and instrumental responding were not
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always large and negative as predicted by interfering response theory. Instead, Tables 3 and 6 showed that the correlations were sometimes weak and the sign of the correlations was inconsistently positive or negative. Second, the within-session changes in instrumental responding were not larger when more adjunctive behaviors were present than when fewer or none of those behaviors were present. The interaction terms in Tables 2 and 5 indicated that the forms of the within-session patterns of instrumental responding rarely differed when adjunctive behaviors were present and when they were not. Figures 1 and 3 also showed that the within-session changes in instrumental responding were not larger for schedules that supported more adjunctive behaviors than for those that supported fewer. Instead, the within-session changes in lever pressing were somewhat smaller during schedules that supported higher rates of adjunctive behaviors, than they were during schedules that supported lower rates. It might be argued that the present FI schedules do not provide a good test of competing-response explanations. Little instrumental responding occurs immediately after reinforcement during these schedules (e.g., Schneider, 1969). Therefore, adjunctive behaviors that occurred at that time would interfere little with instrumental responding. This is a reasonable argument and it implies that an effect of competing responses might be found under other circumstances (e.g., a different choice of schedules). However, the argument does not change the basic conclusion that competition from adjunctive behaviors is not necessary to produce within-session changes in instrumental responding. Within-session changes in instrumental responding were observed during many of the present FI schedules even though competition between instrumental and adjunctive behaviors did not occur. The present results differ somewhat from those reported by Premack and Putney (1962). In that experiment, rats pressed levers for light reinforcers and they were also allowed to drink. Lever pressing increased and then decreased within the session while drinking decreased and then increased. Premack and Putney also compared their results to the results obtained by Premack and Collier (1962) for light-reinforced lever pressing when subjects were not allowed to drink. In that case, lever pressing only decreased within the session. Conclusions based on a comparison of the results presented by Premack and Putney to those presented by Premack and Collier are somewhat suspect. These conclusions rest on a comparison of results across studies and differences in the forms of the within-session changes in responding across studies may be attributed to other procedural differences between the studies, rather than to the presence or absence of drinking. The negative correlation between pressing and drinking reported by Premack and Putney cannot be dismissed so easily. It is not known why a negative correlation was reported in that study, but not in this one. One possible explanation is that the studies used different reinforcers (light vs food). Premack and Putney also employed an unusual procedure in which
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the light remained illuminated as long as the lever was depressed. These explanations for the differences in results across studies require testing, but the results reported by Premack and Putney do not change the conclusion that within-session changes in instrumental responding may occur even when adjunctive and instrumental responding are not negatively correlated. Therefore, changes in interfering adjunctive behaviors cannot provide a complete explanation for within-session changes in operant responding. Interference from two types of adjunctive behaviors did not produce the within-session changes in instrumental responding in the present experiment. However, other interfering responses might contribute to the changes. For example, within-session changes in instrumental responding might be attributed to changes in exploration of the chamber. Future experiments should test these other potential interfering response explanations. The present results do not compel a particular theoretical explanation for within-session changes in responding, but they are consistent with several theories. For example, within-session changes in responding might be attributed to sensitization followed by habituation (e.g., Groves & Thompson, 1970) to aspects of the experimental situation that are presented repeatedly (e.g., reinforcers) or for prolonged periods (e.g., the experimental enclosure). Habituation is assumed to be a primitive form of learning (e.g., Thorpe, 1966) that might occur under a wide variety of circumstances including operant conditioning and adjunctive behaviors. The exact form taken by sensitizationhabituation also changes from preparation to preparation (e.g., Hinde, 1970). Therefore, the form of sensitization-habituation might differ for operant and adjunctive behaviors. Future experiments should more directly test the implications of this and other alternative explanations for within-session changes in responding. Although within-session changes in operant lever pressing were observed in both Experiments 1 and 2, these changes differed in some ways from the within-session changes in operant responding reported in the past. First, the present changes were relatively small. As argued earlier, the ratio of the highest to the lowest percentage of responding was 1.47, 1.26, 1.45, 1.66, and 2.89 for the FI 15-s, FI 30-s, FI 60-s, FI 120-s, and FI 240-s schedules during the water-available conditions in Experiment 1. The same ratios for the wheel-available conditions in Experiment 2 were 1.43, 1.69, 1.19, 2.65 and 2.10. In contrast, ratios, calculated and reported in the same way, were approximately 7, 5, 1, 1, and 2 for pigeons pecking keys for mixed grain (McSweeney, Roll & Weatherly, 1994). Second, within-session changes in responding are often (e.g., McSweeney, 1992), but not always (e.g., McSweeney, Roll & Cannon, 1994), larger and peak earlier for schedules that provide higher, than for those that provide lower, rates of reinforcement. As just indicated, if anything, the present within-session changes were larger for schedules providing lower rates of reinforcement. The location of the peak response rate also changed erratically with changes in the rate of reinforcement. The peak rate of responding was reached during the second, fifth,
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sixth, fifth, and third 5-min intervals for the FI 15-s, FI 30-s, FI 60-s, FI 120s, and FI 240-s schedules, respectively, during the water-available conditions. The peak rate was reached in the fourth, fourth, third or fifth, second and fourth 5-min interval during the same schedules in the wheel-available conditions. A large number of procedural differences between the studies might account for these differences. Future experiments should directly examine some of these procedural explanations. REFERENCES Bindra, D. (1959). Stimulus change, reactions to novelty and response decrement. Psychological Review, 66, 96–103. Duffy, E. (1962). Activation and behavior. New York: Wiley. Falk, J. L. (1971). The nature and determinants of adjunctive behavior. Physiology & Behavior, 6, 577–588. Groves, P. M., & Thompson, R. F. (1970). Habituation: A dual process theory. Psychological Review, 77, 419–450. Herrnstein, R. J. (1970). On the law of effect. Journal of the Experimental Analysis of Behavior, 13, 243–266. Hinde, R. A. (1970). Behavioral habituation. In G. Horn & R. A. Hinde (Eds.) Short-term changes in neural activity and behavior (pp. 3–40). Cambridge, England: Cambridge Univ. Press. Hinson, J. M., & Staddon, J. E. R. (1983). Hill-climbing by pigeons. Journal of the Experimental Analysis of Behavior, 39, 25–47. Hodos, W., & Bonbright, J. C., Jr. (1972). The detection of visual intensity differences by pigeons. Journal of the Experimental Analysis of Behavior, 18, 471–479. Killeen, P. R. (1994). Mathematical principles of reinforcement. Behavioral and Brain Sciences, 17, 105–172. Lowe, C. F., Harzem, P., & Spencer, P. T. (1979). Temporal control of behavior and the power law. Journal of the Experimental Analysis of Behavior, 31, 333–343. McSweeney, F. K. (1992). Rate of reinforcement and session duration as determinants of withinsession patterns of responding. Animal Learning & Behavior, 20, 160–169. McSweeney, F. K., & Hinson, J. M. (1992). Patterns of responding within sessions. Journal of the Experimental Analysis of Behavior, 58, 19–36. McSweeney, F. K., & Roll, J. M. (1993). Responding changes systematically within sessions during conditioning procedures. Journal of the Experimental Analysis of Behavior, 60, 621– 640. McSweeney, F. K., Roll, J. M., & Cannon, C. B. (1994). The generality of within-session patterns of responding: Rate of reinforcement and session length. Animal Learning & Behavior, 22, 252–266. McSweeney, F. K., Roll, J. M., & Weatherly, J. N. (1994). Within-session changes in responding during several simple schedules. Journal of the Experimental Analysis of Behavior, 62, 109–132. Montgomery, K. C. (1953). The effect of activity deprivation upon exploratory behavior. Journal of Comparative and Physiological Psychology, 46, 438–441. Papini, M. R., & Overmier, J. B. (1985). Partial reinforcement and autoshaping of the pigeon’s key-peck behavior. Learning and Motivation, 16, 109–123. Pavlov, I. P. (1928). Lectures on conditioned reflexes (p. 307). New York: International. Premack, D., & Collier, G. (1962). Analysis of non-reinforcement variables affecting response probability. Psychological Monographs: General and Applied, 76, (5, whole number 524). Premack, D., & Putney, R. T. (1962). Relation between intersession interval, frequency of competing responses and rate of learning. Journal of Experimental Psychology, 63, 269– 274.
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Rachlin, H., & Krasnoff, J. (1983). Eating and drinking: An economic analysis. Journal of the Experimental Analysis of Behavior, 39, 385–404. Schneider, B. A. (1969). A two-state analysis of fixed-interval responding in the pigeon. Journal of the Experimental Analysis of Behavior, 12, 677–687. Schoenfeld, W. N., Antonitis, J. J., & Bersh, P. J. (1950). Unconditioned response rate of the white rat in a barpressing apparatus. Journal of Comparative and Physiological Psychology, 43, 41–48. Siegel, S., & Domjan, M. (1971). Backward conditioning as an inhibitory procedure. Learning and Motivation, 2, 1–11. Staddon, J. E. R. (1977). Schedule-induced behavior. In W. K. Honig & J. E. R. Staddon (Eds.), Handbook of operant behavior (pp. 125–152). Englewood Cliffs, NJ: Prentice Hall. Thompson, R. F., & Spencer, W. A. (1966). Habituation: A model phenomenon for the study of neuronal substrates of behavior. Psychological Review, 73, 16–43. Thorpe, W. H. (1966). Learning and instinct in animals (pp. 55–75). Cambridge, MA: Harvard Univ. Press. Received September 20, 1995 Revised November 8, 1995
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