Within-session changes in responding during concurrent variable interval variable ratio schedules.

Rats (Experiment 1) and pigeons (Experiment 2) responded on several concurrent variable interval (VI) variable ratio (VR) schedules. The rate of, but not the time spent, responding in each component usually changed within-sessions. The bias and sensitivity parameters of the generalized matching law (GML) did not change systematically within-sessions. The fit of the GML to the data did not change within-sessions for pigeons, but it was better in the middle than at the beginning or end of the session for some for rats. Both over- and under-matching occurred. These results imply that within-session changes in responding do not usually cause problems for assessing the validity of the GML when subjects respond on concurrent VI VR schedules. The results also suggest that under- and over-matching are not produced by different factors, but rather lie on a continuum.

Habituation contributes to within-session changes in free wheel running.

Three experiments tested the hypothesis that habituation contributes to the regulation of wheel running. Rats ran in a wheel for 30-min sessions. Experiment 1 demonstrated spontaneous recovery. Rats ran more and the within-session decreases in running were smaller after 2 days of wheel deprivation than after 1 day. Experiment 2 demonstrated dishabituation. Running rate increased immediately after the termination of a brief extra event (application of the brake or flashing of the houselight). Experiment 3 demonstrated stimulus specificity. Rats completed the second half of the session in either the same wheel as the first half, or a different wheel. Second-half running was faster in the latter case. Within-session patterns of running were well described by equations that describe data from the habituation, motivation, and operant literatures. These results suggest that habituation contributes to the regulation of running. In fact, habituation provides a better explanation for the termination of wheel running than fatigue, the variable to which this termination is usually attributed. Overall, the present findings are consistent with the proposition that habituation and sensitization contribute to the regulation of several forms of motivated behavior.

The glass ceiling is not fragile: A response to Odum (2000).

Odum (2000) criticized our recent conclusions about the participation of women in the experimental analysis of behavior (McSweeney & Swindell, 1998). We address her criticisms here. We argue against the need for statistical tests. We show that our conclusions still apply to all journals except the Journal of the Experimental Analysis of Behavior even when we include the senior editorial staff along with members of the editorial board. We argue that the data that Odum provides to show gender equity are limited, inconsistent with past findings, and hard to interpret in the absence of other data. Finally, we argue that Odum failed to address our most convincing argument for gender inequity and misinterpreted our suggestions for improvements.

Criticisms of the satiety hypothesis as an explanation for within-session decreases in responding.

The authors of four papers recently reported that satiation provides a better explanation than habituation for within-session decreases in conditioned responding. Several arguments question this conclusion. First, the contribution of habituation to within-session changes in responding seems clearly established. Information that is consistent with habituation, but that is difficult to reconcile with satiation, is not adequately addressed. Second, the limited evidence offered in support of satiation is ambiguous because the results are just as compatible with habituation as with other satiety variables. Finally, the term satiation is used in an intuitive way that is sometimes contradicted by research about the termination of ingestion. Use of the technical term satiation in a way that differs from its conventional usage will only isolate operant psychology from other areas of psychological research.

Women in applied behavior analysis.

The status of women in applied behavior analysis was examined by comparing the participation of women in the Journal of Applied Behavior Analysis (JABA) to their participation in three similar journals. For all journals, the percentage of articles with at least one female author, the percentage of authors who are female, and the percentage of articles with a female first author increased from 1978 to 1997. Participation by women in JABA was equal to or greater than participation by women in the comparison journals. However, women appeared as authors on papers in special sections of Behavior Modification substantially more often when the editor was female than when the editor was male. In addition, female membership on the editorial boards of JABA, Behavior Modification, and Behaviour Research and Therapy failed to increase from 1978 to 1997. We conclude that a "glass ceiling" reduces the participation of women at the highest levels of applied behavior analysis and related fields.

Behavioral economics and within-session changes in responding.

Pigeons and rats responded on fixed-ratio schedules with requirements ranging from 5 to 120 responses. Consistent with past results from several schedules and procedures, responding usually changed systematically within experimental sessions. The within-session changes were usually larger and were less symmetrical around the middle of the session for schedules that provided higher, rather than lower, rates of reinforcement. These results suggest that similar variables contribute to within-session changes in responding under different schedules. When an economic demand function was fit to the data, the intensity and elasticity of demand for food and the percentage of the variance accounted for decreased within sessions, although the trend for elasticity did not reach statistical significance for pigeons. These results suggest that relatively short sessions should be used to study economic demand in open economies and that demand may differ at different times in a session and in sessions of different lengths. Within-session changes in intensity, but not necessarily elasticity, of demand are consistent with behavioral economic theories.

Women in the experimental analysis of behavior.

We examined the status of women in the experimental analysis of behavior by comparing authorship by women in the Journal of the Experimental Analysis of Behavior (JEAB) to authorship by women in three similar journals. For all journals, the percentage of articles with at least one female author, the percentage of authors who are female, and the percentage of articles with a female first author increased from 1978 to 1997. However, the participation by women in JEAB lagged behind participation in the other journals on each measure. Female membership on the editorial board of JEAB also failed to increase from 1978 to 1997. Suggestions are made that may increase the participation of women in the experimental analysis of behavior.

The effects of stopping and restarting a session on within-session patterns of responding.

Rats pressed levers for sweetened condensed milk reinforcers delivered according to a multiple variable-interval 1-min, variable-interval 1-min schedule during 60-min baseline sessions. The obtained pattern of responding was an early-session increase in responding followed by a relatively constant rate of responding during the remainder of the session. In the experimental conditions of experiment 1, sessions were interrupted by a blackout or timeout lasting either 5, 10, or 30 min. Responding following 5- or 10-min interruptions resembled the constant rate of responding late in the baseline sessions. However, responding increased before 30-min interruptions and increased again after the interruption. This change in the pattern of responding was best described as a `restarting' of the within-session pattern of responding. In experiment 2, a 30-min blackout interrupted sessions. However, reinforcers were presented intermittently during the blackout. Responding did not restart following the 30-min blackout-with-reinforcers condition. These results suggest that the mere presentation of reinforcers is sufficient to maintain within-session changes in responding.

Exposure to context may contribute to within-session changes in responding.

Rats and pigeons responded on multiple variable interval 30-s variable interval 30-s and multiple variable interval 60-s variable interval 60-s schedules. The 60-min sessions began 0, 5, 10, 15 or 30 min after the subject was placed in the experimental enclosure, determined randomly. Early-session response rates were usually higher, and the early-session increases in responding were usually smaller, when the beginning of the session was delayed than when it was immediate. These results show that factors related to reinforcement (e.g. satiation, sensitization-habituation to the reinforcers) do not provide a complete explanation for within-session changes in operant responding. Instead, an additional factor, possibly arousal or sensitization to the experimental context, also contributes. The results suggest an explanation for the spontaneous recovery of extinguished behavior.

Within-session patterns of responding with changes in the variability and probability of food delivery.

The present study was an attempt to determine the factors to which subjects sensitize and/or habituate within experimental sessions. Rats pressed a lever and pigeons pecked a key for food reinforcers delivered during a 60 min session. In experiment 1, subjects initially responded on a simple variable-interval 30 s schedule that consisted of 25 intervals. In subsequent conditions, the number of intervals in the series was decreased until subjects responded on a simple fixed-interval 30 s schedule. In experiment 2, subjects always responded on a variable-interval 15 s schedule that resulted in a stimulus change. The probability that a food reinforcer would accompany the stimulus change varied across conditions. Results showed that within-session patterns of responding did not change for either species with changes in the temporal pattern of reinforcer delivery (experiment 1). The within-session response patterns generally became flatter with decreases in the probability of food delivery for both species (experiment 2). The present results indicate that subjects are sensitizing and/or habituating to the reinforcer itself and/or to some aspect of its delivery. They also help to highlight the strength of sensitization-habituation as an explanation for within-session changes in responding.

Within-session changes in responding during concurrent schedules with different reinforcers in the components.

Rats and pigeons responded on several concurrent schedules that provided different reinforcers in the two components (food and water for rats, Experiment 1; wheat and mixed grain for pigeons, Experiment 2). The rate of responding and the time spent responding on each component usually changed within the session. The within-session changes in response rates and time spent responding usually followed different patterns for the two components of a concurrent schedule. For most subjects, the bias and sensitivity to reinforcement parameters of the generalized matching law, as well as the percentage of the variance accounted for, decreased within the session. Negative sensitivity parameters were sometimes found late in the session for the concurrent food-water schedules. These results imply that within-session changes in responding could cause problems for assessing the validity of quantitative theories of concurrent-schedule responding when the components provide different reinforcers. They question changes in a general motivational state, such as arousal, as a complete explanation for within-session changes in responding. The results are compatible with satiation for, or sensitization-habituation to, the reinforcers as explanations.

Reinforcer value may change within experimental sessions.

Large and systematic changes in response rates often occur within sessions during operant conditioning procedures. In the present experiment, we asked whether the value of the reinforcer that supports responding also changes within sessions. Pigeons pecked a key for mixed grain available throughout the session. Occasionally, wheat was also provided for pecking a second key. The ratio of the rates of responding for mixed grain and wheat, a frequently used measure of relative reinforcer value, changed significantly within sessions when mixed grain was provided at high, but not at low, rates. Habituation to the reinforcer provides the most likely explanation for these changes in reinforcer value. Eventually, habituation may provide a unified explanation for the within-session changes in behavior that occur when many species of subjects respond on a wide variety of tasks.

Knowledge of session length is a determinant of within-session response patterns in a human operant paradigm.

Two experiments were conducted during which undergraduates responded during a variable-interval (VI) 60-second operant task. The first experiment consisted of either three 60-minute sessions or three 30-minute sessions. During Experiment 1 subjects were informed as to the length of the session and the number of sessions that would be conducted. During the second experiment subjects were told that they would be participating in three 60-minute sessions but they actually participated in one 30-minute session. During Experiment 1 the rate of responding increased significantly within the sessions for 30-minute sessions but did not change significantly for 60-minute sessions. Response rate did not change during the 30-minute session in Experiment 2. The results of these experiments demonstrate that, under certain circumstances, rate of responding changes within-sessions for humans. The experiments also provide some evidence that a prospective factor influences the rate of responding within an experimental session for human subjects.

Within-session changes in responding during variable interval schedules.

Four rats and four pigeons responded for food delivered by variable interval schedules that provided programmed rates of reinforcement ranging from 15 to 480 reinforcers per hour. Rate of responding increased, decreased, or increased and then decreased within sessions. The within-session pattern of responding changed with changes in the programmed rate of reinforcement and with the species of subject. Finding within-session changes in responding during variable interval schedules extends the generality of these changes to another schedule. It implies that variable interval schedules should be used cautiously as baselines for assessing the effects of other variables, such as drugs. Finally, the results suggest that systematic pauses in responding during the session may contribute to the decreases in the average rates of responding with increases in the rates of reinforcement that are sometimes observed when subjects respond on variable interval schedules that deliver high rates of reinforcement.

A preliminary examination of some effects of cocaine on within-session patterns of responding.

Two experiments examined within-session changes in operant responding when cocaine or cocaine plus food served as the reinforcer. In Experiment 1, male rats self-administered intravenous cocaine according to several fixed interval schedules. The within-session patterns of responding differed for the different schedules early in the session, but they converged by 50 minutes into the session. Because this convergence occurred regardless of the amount of cocaine consumed, it questions the response-stereotypy and dopamine-loading explanations for within-session changes in responding for cocaine reinforcers. In Experiment 2, rats responded for sweetened condensed milk during baseline sessions. During experimental sessions, responding produced cocaine in addition to the condensed milk. The addition of cocaine altered the pattern of responding during the early (first 15 minutes), but not the later (last 45 minutes), parts of the session. These results suggest that different factors produce the early-session increases and late-session decreases in responding. They are also consistent with the idea that the early-session changes in responding represent changes in'arousal'.

Within-session response rates when reinforcement rate is changed within each session.

Three pigeons pecked keys and 5 rats pressed levers for food delivered on variable-interval schedules. During baseline conditions, subjects responded on a variable-interval 40-s schedule throughout the session. During experimental conditions, the programmed rate of reinforcement changed every 10 min in the 50-min sessions. When rats served as subjects, Herrnstein's (1970) hyperbolic equation provided a good description of the relation between rate of responding during a 10-min interval and the rate of reinforcement obtained during that interval. Responding, measured over 10-min blocks, was also approximately equally sensitive to changes in the programmed rate of reinforcement at all times in the session. Herrnstein's equation provided a poorer description of the changes in responding when pigeons served as subjects. Differences in experimental experience or differences in the absolute rates at which subjects responded may have contributed to the differences in results for these different species.

Within-session changes in key and lever pressing for water during several multiple variable-interval schedules.

Rats pressed keys or levers for water reinforcers delivered by several multiple variable-interval schedules. The programmed rate of reinforcement varied from 15 to 240 reinforcers per hour in different conditions. Responding usually increased and then decreased within experimental sessions. As for food reinforcers, the within-session changes in both lever and key pressing were smaller, peaked later, and were more symmetrical around the middle of the session for lower than for higher rates of reinforcement. When schedules provided high rates of reinforcement, some quantitative differences appeared in the within-session changes for lever and key pressing and for food and water. These results imply that basically similar factors produce within-session changes in responding for lever and key pressing and for food and water. The nature of the reinforcer and the choice of response can also influence the quantitative properties of within-session changes at high rates of reinforcement. Finally, the results show that the application of Herrnstein's (1970) equation to rates of responding averaged over the session requires careful consideration.

Prospective factors contribute little to within-session changes in responding.

Five rats pressed levers for food delivered by a multiple variable interval 1-min variable interval 1-min schedule. In theunpredictable conditions, sessions were 20, 40, 60, 80, or 100 min long, determined randomly at the beginning of each session. In thepredictable conditions, each of these session durations was presented for 15 consecutive sessions. Rate of responding changed systematically within the session even when the end of the session was unpredictable. This implies that prospective factors related to anticipation of the end of the session are not necessary for producing withinsession changes in responding. Within-session patterns of responding were also similar for the predictable and unpredictable conditions. This suggests that prospective factors contributed little to the form of the within-session patterns under the present conditions.

Within-session response patterns when rats press levers for water: Effects of component stimuli and experimental environment.

Rats pressed levers for water reinforcers delivered by multiple variable interval one-minute variable interval one-minute schedules. Experiment 1 manipulated the stimuli signalling the components of the multiple schedule. Experiment 2 varied the experimental environment. Responding changed significantly within the session during every condition of both experiments. Manipulating the component stimuli significantly altered the within-session pattern of responding; varying the environment did not. These results show within-session patterns of responding occur when subjects respond for water reinforcers. They also imply that contextually-based explanations for within-sessions patterns of responding are unlikely.

Within-session changes in responding when rate and duration of reinforcement vary.

Three pigeons responded on variable interval 60-second and variable interval 30-second schedules. The duration of access to mixed grain was varied from 2-to 20-seconds per reinforcer in different conditions. Within-session patterns of responding did not differ when subjects received 2- versus 20-seconds access to the reinforcer for the schedule providing the lower rate of reinforcement. However, the within-session decreases in responding were steeper when reinforcers were 20-seconds than when they were 2-seconds for the schedule providing the higher rate of reinforcement. These results indicate that satiation is not necessary to produce within-session changes in responding, but it may contribute to those changes at high rates of reinforcement.