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Running Head: WITHIN-SESSION PATTERNS OF RESPONDING



Rate of a Maintained Operant as a Function of Temporal
Position Within a Session

William L. Palya and Donald E. Walter
Department of Psychology
Jacksonville State University
205-782-5641
palya@sebac.jsu.edu







Cover Page

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Abstract

McSweeney and her colleagues (e.g., McSweeney, Hatfield, & Allen, 1990) have demonstrated reliable, large magnitude rate changes in maintained operants within daily sessions under a wide variety of reinforcement schedules. The present paper examined the role of schedule of reinforcement, reinforcement rate, and total amount of food access in determining those within-session rate changes. If median rates across birds were considered, then all procedures resulted in a brief period of an increasing rate, followed by a modest rate loss across the major portion of the session. However, not all individuals exhibited that pattern. When the amount of food access per session was limited by lower reinforcement rates, shorter sessions, or shorter reinforcement durations, then the magnitude of the within-session rate change was reduced from that occurring without those constraints. Additionally, under the conditions that produced strong within-session rate changes, the magnitude of the within-session rate loss was correlated with the bird’s body weight. These effects are consistent with what is typically labeled satiation.






Abstract

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Rate of a Maintained Operant as a Function of Temporal Position Within a Session

McSweeney and her colleagues (McSweeney, Hatfield & Allen, 1990; McSweeney & Hinson, 1992; McSweeney, Roll & Weatherly, 1994) have documented systematic changes in operant responding as a function of temporal position within each daily exposure to a schedule of reinforcement (i.e., a session). Their extensive functional analyses have typically indicated a relatively short duration period during which the response rate increases followed by a generally decreasing rate throughout the remainder of the session. This bitonic rate change is of importance for three reasons. First, to the degree that it is reliable, it must be studied if a coherent and complete understanding of schedule control, and a general understanding of behavior, is to be accomplished. Second, a changing rate across the session would mean that any single index of behavior collapsed across a session can correctly represent only that, or larger quantal units, rather than behavior in general. Finally, if behavior systematically changes across a session, then any within-session experimental treatment confounds that treatment with the bitonic effect. There would be important ramifications of this confound with respect to our body of accumulated knowledge (McSweeney, 1992).

However, the literature suggests that the bitonic within-session effect may not be ubiquitous. Examination of cumulative records in Ferster and Skinner (1957) do not suggest a rate change on the order of 450% across a session, as was obtained by McSweeney, Hatfield, & Allen (1990). The current practice of collapsing data across a session into a single index indicates that the bitonic effect had either not been noticed, or had not been considered significant by most researchers before McSweeney's 1992 observation. Moreover, studies explicitly depicting behavior as a function of time in the session have not always shown the bitonic effect (McSweeney et al., 1990; Palya, 1992).





Introduction

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Start with something everyone will agree with. Address yourself to psychologists who have a good general knowledge of introductory psychology, but who may not remember all the exact details. Be impersonal in style. Do not use interrogatory sentences or question marks. Use declarative statements and periods instead.

The Introduction section answers the WHY questions surrounding the research. This section gives the reader enough background to understand the relevance, the point, and the meaning of the research question. It also develops a case for the appropriateness and the necessity of the procedures used to answer the research question.

Develop how your research fits into the field of psychology as a Euclidean proof. Initially present the overall subject matter and its relevance. Then develop how your research question evolved historically. Review the issue which originally raised the problem. Present the succession of answers and subsequent questions revolving around the problem. Demonstrate the importance and significance of your research question by pointing out the impact that various possible results would have. Be careful to maintain the continuity of the developing issue, and to provide adequate contact with the literature (i.e., references).

Make a case for why the procedure that you intend to use is the most appropriate method for demonstrating or determining the effect. Also develop a case for why the actual independent variable and dependent variable are acceptable models for the inferred independent and dependent variables if you do not discuss them in their own terms. Note that the procedure must not be unnecessarily complex, and that the ensuing results must not be subject to alternative explanations.



Method

Subjects

Twelve adult, experimentally naive pigeons obtained from a local supplier, were used. They were housed under a 19:5 hr light:dark cycle in individual cages with free access to water. All were maintained with pelletized laying mash. As determined by each bird’s presession body weight, the number of reinforcers in a session was adjusted from its typical value of 50, so that each bird would be at 80% of its free-feeding weight at the beginning of the next session.





Subjects

Include how many, what species, the population from which they were selected, and any other pertinent details concerning the subjects in particular. Provide the information necessary to replicate the study with respect to subjects. The information should enable the reader to realize any confounds or inability to generalize because of special property of the subjects.



Apparatus

Five experimental chambers were used. The interior of each was a 30 cm cube painted white. A stimulus panel served as one wall of the chamber. It had a feeder aperture medially located 8 cm above the grid floor. Three symmetrically positioned response keys, 2 cm in diameter, were located 9 cm apart, 19 cm above the grid floor. They required approximately 0.15 N to operate. The translucent Plexiglas keys could be transilluminated lime green by a stimulus projector containing a Rosco theatrical color filter. Two houselights were located on the stimulus panel 28 cm above the grid floor and 9 cm apart. Ventilation was provided by an exhaust fan mounted on the outside of the chamber. A white-noise source provided ambient masking noise.

Stimulus events were controlled and key pecks were recorded by a computer system (Palya & Walter, 1993). The computer archived the time of each stimulus and response event in 1-ms “ticks.” Subsequent data extraction and analysis routines provided the resulting behavioral indices. Complete raw data event logs of all research are maintained for 10 years and are available via internet upon request (see Authors’ Note).





Apparatus

Describe the apparatus sufficiently enough that some-one could replicate your study with respect to apparatus or setting. When a "standard" apparatus is used, name it and then go on to describe it.

Describe the apparatus only insofar as it interacts with the subject. Describe the properties not what it did or what it was used for. If it was not used, do not describe it unless it was of overshadowing importance. Do not describe the way the apparatus interacts with the experimenter unless it has a direct bearing on the procedure or the results. Provide all the information necessary to allow the reader to realize any confounds or inability to generalize because of some special property of the apparatus or setting. You must use the Standard International System of Units.



Procedure

Each bird was exposed to a series of variable ratio (VR) schedules of differing requirements. These schedules provided a 3-s reinforcer for the first key peck following a variable number of key pecks with the specified mean. A 20-element Fleshler-Hoffman series (Fleshler & Hoffman, 1962) was used to generate the distribution of response requirements for the VR schedule. In separate phases, each bird also received VI schedules and VI+ schedules (McDowell & Kessel, 1979) yoked to the reinforcement rate obtained under its VR procedures. A VI+ schedule is a synthetic schedule that reinforces the first response after a temporal interval which itself is a function of the average interresponse time (IRT) for that interreinforcement interval (IRI). Because of the way it was scheduled, a bird's VI+ schedule necessarily had the same mean reinforcement rate as the VR to which it was yoked. Each bird also received a VI schedule yoked to its reinforcement rate under the VR. Note that for ease of designating the appropriate schedule value for comparison, and for ease of labeling the VI and VI+ values for the 12 birds under the 15 conditions, those schedule values were specified as the VR value to which they were yoked. For example, a VI which was yoked to a VR 100 (i.e., a VI prime schedule or VI' 100) had the same IRI as that bird's VR 100. Across birds, the mean IRI for the VI' 10, 50, 100, 200 and 400 schedules were 5, 24, 50, 103 and 218 s, respectively. This simple labeling convention eliminated the need to specify 60 different VI schedule values and the tables indicating which VI value corresponded to which VR values for each bird.

Each procedure was implemented with each bird (balanced across birds) until responding was judged stable by time-series analysis on eight consecutive mean daily response rates (Tryon, 1982; von Neumann, Kent, Bellinson, & Hart; 1941; Young, 1941) and the judgment of stability was confirmed by visual inspection. The session duration for a bird on a given day was determined by the number of reinforcers necessary to maintain the bird at its 80% body weight or 50 reinforcers (30 when the schedule value was 400), whichever was smaller. The session duration, therefore, varied somewhat from day to day and more substantially from schedule to schedule. For example, at the lowest reinforcement rate, sessions were approximately 100 min long, whereas at the highest reinforcement rate, sessions were approximately 4 min long. The session length and therefore the opportunity to observe long duration within-session effects necessarily varied because schedule value, amount of food presented, and session length could not be simultaneously controlled. Simply put, each bird was exposed to each of the following procedures for between 10 and 30 sessions: VR 10, 50, 100, 200, and 400; VI+10, 50, 100, 200, and 400-s; and VI' 10, 50, 100, 200 and 400-s.





Procedure

The reader must know everything that happened to the subject, all of the information necessary to replicate the study. Procedures are written in terms of a sequence of events. Give an overall view then a detailed description. Include instructions, maintenance schedule, how the independent variable was administered, and how the dependent variable was recorded. If there were instructions given to the subjects you would quote them in this section if necessary, or refer the reader to an appendix. Provide all of the information necessary to realize any confounds or inability to generalize because of some special property of the procedure. If data cannot be replicated through your procedure section your contribution cannot be considered a fact, and is of little use. The actual controlling variable was obviously unspecified.







Method

The Method section consists of the Subjects, Apparatus, and Procedure sections. It tells the reader precisely how the experiment was conducted and all the information necessary to recognize confounds. Include everything necessary to replicate and obtain the same results and nothing that is unnecessary. Include the relevant, exclude the irrelevant. There is no introduction following the word Method. The first line of the section is the title of the Subjects section.



Results

Description of Behavior. Overall, the procedures of Experiment 1 resulted in only a modest decline in rate across the session. None of the reinforcement rates or schedules of reinforcement resulted in large within-session rate changes when total amount of food access was held constant by adjusting the session length. Based on single, straight-line, least squares characterizations, the three schedules and the five reinforcement rates all had similar slopes. An analysis of variance (11 subjects x 3 schedules x 5 reinforcement rates) indicated that the obtained slope differences due to schedules and reinforcement rates were not significant (p<0.99 and 0.94, respectively). The median slope varied from -0.07 to -0.19 for schedules (collapsed across reinforcement rates and birds) and from -0.01 to -0.48 for reinforcement rates (collapsed across schedules and birds). Collapsed across schedules, reinforcement rates and birds, the median slope was -0.06. Lastly, while many functions (as characterized by 20-s bins) showed atypical responding immediately following the beginning of the session, many other functions appeared, for the most part, relatively linear throughout the session.

The first and second segment slopes were subjected to an analysis of variance (11 subjects x 3 schedules x 5 reinforcement rates). The first segment slopes did not differ as a function of schedule or reinforcement rate (p<0.66 and 0.18, respectively). The second segment slopes did differ as a function of schedule (p < 0.04), but not as a function of reinforcement rate (p<0.84). The interaction was also significant (p<0.01). In order to better understand the source of that interaction and the marginal significance of the schedule effect, an additional ANOVA of the second segment slopes which excluded the highest reinforcement rate was carried out. It was not significant (p<0.18 and 0.92 for schedules and reinforcement rates, respectively). Table 1 presents the median within-session rate change indices and variance accounted for by body weight for the procedures of Experiment 2.

The 12 initial slopes (one for each bird) under each of the 15 procedures were displayed in a single frame. The upper left frame of Figure 1 provides the lines fit to the initial segments of the within-session rate change normalized to the last data point preceding the breakpoint (a “backward” plot). The center left frame provides a similar but “forward” depiction for the second segment fits. To the right of each of these frames is a histogram of the respective slopes for all 12 birds across all 15 procedures.





Results

First briefly present the main trend of the findings with respect to the main procedural manipulation. Then logically present the relevant results of the procedure. Order your presentation with respect to categories of results. Summarize your data, avoid presenting raw data. Present or show data to justify your assessment of the major trends. You MUST prove your points and not just state them. Provide quantitative measures. Present evidence supporting the reliability of the data, and the amount of variance your descriptions will account for. Additionally provide information which will allow the reader to realize the magnitude of the effect which would be necessary before it was reported as reliable. Do not introduce theory or interpretations in this section. This is a data section. Keep in mind that your topic is Psychology and that the behavior of the organism (not the organism) is the dependent measure. Describe the behavior, not the organism. A handy rule of thumb is "you should avoid altogether any reference to the subject (the organism) in the results and discussion sections. For example, "the response rate increased ...." rather than "the pigeon pecked faster".







Figures and Tables

Present figures and tables if appropriate. You may never include figures or tables without referring to them in the manuscript text. The most important points brought out in the table or figure must also be stated in the results section. Put the actual figures or tables at the end of the paper.



Discussion

The experiments of the present study demonstrated that: (1) none of the 15 combinations of schedules and reinforcement rates produced a large within-session response rate change when the number of reinforcers given in a session was restricted, (2) a high reinforcement rate with a long session length did result in a tendency toward a strongly bitonic rate change over a session, but that rate change was correlated with the bird’s body weight, and finally, (3) the same long exposures to a reinforcement rate which had produced strongly bitonic rate changes with normal reinforcement durations did not result in large within-session rate changes if the bird’s access to food was limited to one bite per reinforcer.

Taken together these findings suggest that the degree of within-session rate change is a function of some factor correlated with the amount of food access in a session per unit of body weight. Such a process is consistent with what most researchers refer to when they use the term satiation. However, as McSweeney and her colleagues (McSweeney, Hinson, & Cannon, 1996; Roll, McSweeney, Johnson & Weatherly, 1995) have aptly pointed out, this is only a label for what is actually a poorly understood mechanism. For example, while the current usage of satiation comfortably fits the tendency for most birds to exhibit a rate loss across the session; the traditional meaning poorly fits the instances showing rate gains across the initial portion or even across the entire session.

McSweeney has argued that her theoretical approach is superior to the simple notion of satiation. Her position is that the initial rising portion of the within-session rate change is the result of sensitization and is best described by a positive hyperbola. The sustained rate loss across the major portion of a session is seen as habituation and best described by a negative exponential. Overall, the within-session rate change is therefore described by the algebraic difference of those two processes. McSweeney has demonstrated the systematic character of her position by showing that the same model could describe both the change in a maintained operant across a session, as well as data from the sensitization and habituation literature (McSweeney, Hinson, & Cannon, 1996).

There are three conceptual alternatives to the issue raised by McSweeney; they are: (1) retain the term satiation but clarify its specific definition and elaborate its specific functional properties, (2) show that both satiation and a wide variety of other phenomena can best be seen as instances of the more fundamental processes of sensitization and habituation. Paradigmatic development within this second framework would entail adjusting definitions to fit the emerging empirical framework. And finally, (3) reify the traditional definition of satiation and therefore reject its appropriateness as an explanation for the within-session effect. Theoretical development within this third approach would be the elaboration of the referents for the terms sensitization and habituation and the systematization of their functional properties. McSweeney (McSweeney, Hinson, & Cannon, 1996) has taken this third alternative. She has asserted that the within-session rate change is the result of sensitization and habituation and has rejected satiation as a useful term.

The present study clarified the determinant of the within-session response rate change. That change is at least partly under the control of food access per unit of body weight during the session. This is what is typically implied by the term satiation. The issues pertaining to the effect which remain to be resolved are the development of a quantitative model for satiation or whatever label is given to the process, and the determination of a coherent way of dealing with the variability across individuals.





Discussion

The Discussion section answers the question "SO WHAT?" or "WHAT OF IT?" It discusses what the results of the research mean. Open this section with a clear state- ment of support or lack of support of the original hypothesis presented in the Introduction. Discuss the questions which were asked in the introduction, what the answers were, and in what sense the data answered these questions. Recap data to prove the answer to the question regardless of whether they were affirmative or negative. Recap the reliability and generality of your results. It is necessary to nonstatistically substantiate your results and their reliability and generality by citing other similar or related studies and their findings. Point out similarities and differences between your findings and other findings and relate those differences to the procedural differences. Cite examples of other similar results. Discuss how your findings are similar to other kinds of research. Help substantiate your conclusions by pointing out functional similarities and the relevance to your conclusions.

The data will answer some questions more than others. Talk about the conclusions which can be made from the data, e.g., "it may be concluded that this drug has the effect of increasing the rate of ....." Make partial conclusions. State the limitations, qualifications, and generalizations of your statements. If necessary, describe the limitations in detail. A potential limitation is that the results may be peculiar to the procedure.

Discuss the certainty with which the data answer the various questions. Use "but" and "however" type sentences, e.g., "these data suggest this, however, such and such may not have been controlled. What other alternative interpretations are there? Rule them out with evidence or explore their potential. In the end you may have discovered a better question rather than a better answer. If that is the case discuss exactly that.

This section is your conclusion and not your results. It is what you think about your results and what they mean, not just a repeat of the results section. Remember that your data are real and not hypothetical. It is assumed that you have thought about the ramifications and implications of your research more than anyone else, however never be final or eternal about your conclusions. Never end a discussion with an appeal for more research to be done.






REFERENCES

Collier, G., Hirsch, E., & Kanarek, R (1977). The operant revisited. In W. K. Honig & J. E. R. Staddon (Eds.), Handbook of operant behavior. Englewood Cliffs, NJ: Prentice-Hall.

Ferster, C. B., & Skinner, B. F. (1957). Schedules of reinforcement. Englewood Cliffs, NJ: Prentice Hall.

Fleshler, M., & Hoffman, H. S. (1962). A progression for generating variable-interval schedules. Journal of the Experimental Analysis of Behavior, 5, 529-530.

McDowell, J. J., & Kessel, R. (1979). A multivariate rate equation for variable-interval performance. Journal of the Experimental Analysis of Behavior,31, 267-284.

McSweeney, F. K. (1992). Rate of reinforcement and session duration as determinants of within-session patterns of responding. Animal Learning & Behavior, 20, 160-169.

McSweeney, F. K., Hatfield, J., & Allen, T. M. (1990). Within-session responding as a function of post-session feedings. Behavioural Processes, 22,177-186.

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., Hinson, J. M., & Cannon, C. B. (1996). Sensitization-habituation may occur during operant conditioning. Psychological Bulletin, in press.

McSweeney, F. K., & Johnson, K. S. (1994). The effect of time between sessions on within-session patterns of responding. Behavioural Processes, 31, 207-218.

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, 252-256.

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.





References

Begin this section on a separate page. The above examples cover the common types of entries. Pay very close attention to the format. Note that the titles of the journals are written out in full. Also note what is and what is not capitalized (e.g., in book titles, only the first letter of the first word is capitalized and also the first letter following a colon; in journals the first letter of each major word is capitalized). Book titles, names of journals, and volume numbers of journals are underlined.

The text should make adequate contact with relevant literature through references. You must provide the source of your information that interested readers can go to the original sources themselves to expand or confirm what you said. Science does not believe things just because someone said them, but because the facts have been substantiated by many independent investigators with "different axes to grind." Findings must be understandable and replicable to both people who agree with your interpretation and to those who disagree.



Authors' Note

Portions of this paper were presented at the annual meeting of The Psychonomic Society, 1995. The authors gratefully acknowledge the contributions of Helen Bush and Josey Chu for running the animals; Robert Allan, Edmond Venator, and Robert Kessel for critical discussions; Peter Killeen and Frances McSweeney for comments on an earlier draft of this paper; and Elizabeth Palya for contributions in all phases of this research. Correspondence and requests for reprints should be sent to William L. Palya, Department of Psychology, Jackson- ville State University, Jacksonville, AL 36265 (e-mail: palya@sebac.jsu.edu).





Authors' Note

This section specifies the grant support, as required by most granting agencies. If parts of the research were presented at a meeting, state that information. Any acknowledgments are also indicated in this section. Finally, an address where reprints may be obtained is given.



Table 1

Median Within-Session Rate Change Indices and Variance Accounted for by Body Weight for the Procedures of Experiment 2



One Line
First
Second
McSweeney
Schedule
slope
r2
slope
r2
slope
r2
“a”
r 2
VI 120
-0.10
-0.02
0.59
-0.02
-0.07
-0.01
0.31
-0.02
VI 60
-0.09
0.08
0.35
-0.02
-0.06
0.05
0.30
0.01
VI 30
-0.11
-0.01
0.99
-0.02
-0.10
0.06
0.39
0.14
VI 15
-1.06
0.18
-0.27
-0.01
-1.26
0.11
0.98
0.15
VI 60
-0.06
-0.01
0.99
-0.02
-0.10
-0.01
0.30
-0.01
VI 15(1B)
-0.09
0.00
0.02
-0.02
-0.04
0.07
0.30
0.04






Tables

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Figure Captions

Figure 1. The upper left frame depicts the slopes of the first segment of the best two-line fit for each bird under each procedure. The upper right frame depicts the frequency distribution of those slopes. The center left frame presents the slopes of the second segment of the best two-line fit for each bird under each procedure. The center right frame presents the frequency distribution of second segment slopes. The lower left frame reports the frequency distribution of the difference in each bird’s slopes, while the lower right frame presents the frequency distribution of the breakpoints.

Figure 2. Each frame depicts the rate of the operant as a function of time in the session for each of the 45 birds. The six frames depict the data from the six procedures. The consecutive procedures in the experiment are presented in consecutively lower frames.





Figure Captions

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Figures
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Date Last Reviewed: May 26, 2003