Operant response rate can be viewed as bouts, periods of alternating engagement and disengagement with ongoing schedules of reinforcement. Relatively few studies have examined the role of force and effort on engagement bouts. Moreover, those examining effort have used switch closure devices to define the response. Switch closures tend to overestimate the effect of effort because increasing the force requirement excludes low-force responses that previously activated the switch. In the present study, we examined the effects of effort using a force transducer, which allows us to record criterion responses that meet the force requirement and subcriterion responses that do not. The current study was conducted using four male Sprague Dawley rats. Each rat was run through a series of four conditions, each with a different combination of variable interval schedules (VI 30s, VI 120s) and force requirements (5.6g, 32g). Log survivor analyses of bout structure showed that increased force requirements decreased the rate of bout initiations. Additionally, when log-survivor functions were computed using only criterion responses, shifts in the function were less extreme than when all measured responses were used; the latter finding suggests exclusion of "subcriterion" responses in prior work has overestimated the effects of force on bout structure

Behaving in novel ways is essential to the development of the types of complex performances described by the term creativity, problem solving, and perseverance. Some research suggests that response variability is an operant and a critical component of novel behavior. However, other account of novel behavior may be more parsimonious. Topographical variability has rarely been examined, nor has operant variability with organisms with baselines featuring stereotypic responding. This study examined the effects of a variability-specifying contingency on the cumulative novel responses of undergraduate students. Using the PORTL apparatus, participants interacted with a ball with a single hand. When the variability-specifying contingency was in effect, novel topographies were reinforced. When a reinforce every response condition was implemented, the participants did not emit any novel responses. When variability-specifying contingencies were in effect, novel responses were rarely followed by subsequent novel responses. They were mostly followed by repeated emission of the same topography, or by other previously emitted topographies. Novel responding did not persist long, although the variability-specifying contingency remained in effect and the potential for novel responding was great. The variability-specifying contingency often resulted in stereotypic response chains. Each of these findings call into the question the assertion that variability is an operant and suggests other possible explanations for the observed novelty.

Bipolar disorder is characterized by disruptions in mood and affect that occur not only during mood episodes, but during euthymic periods as well. At the same time, sensitivity of the behavioral activation system (BAS) has been implicated in the disorder and is a risk marker for it. Less clear is the relationship between BAS sensitivity and positive affect, particularly lower level facets of positive affect. The aim of the present study was to examine the relationship between positive affect and vulnerability for mania as assessed using BAS sensitivity. Specifically, the link between daily levels and fluctuations of positive affect and baseline BAS sensitivity was examined. Following the hierarchical model of affect, this study also assessed the relationship between BAS sensitivity and the distinct facets of positive affect. Finally, this study examined whether BAS sensitivity moderates associations between daily rewards and positive affect. Undergraduates (N = 265) from a large university in the South were recruited to complete measures of BAS sensitivity, affect, and mood symptoms at baseline. Using ecological momentary assessment (EMA), participants completed daily surveys assessing affect and engagement with rewarding situations. An exploratory factory analysis revealed a four factor structure of positive affect, consisting of Serenity, Joviality, Attentiveness, and Self-Assurance. Greater daily levels of overall positive affect, as well as the lower order facets of Joviality, Self-Assurance, and Attentiveness, were predicted by heightened BAS sensitivity. In contrast, the facet of Serenity demonstrated minimal associations with BAS sensitivity. The study findings support a multi-faceted structure of positive affect and suggest that certain facets may be more closely related to risk for bipolar disorder. Specifically, Joviality and Self-Assurance may represent maladaptive forms of positive affect, whereas Serenity may function as a protective element against bipolar disorder.

Positive and negative reinforcement contingencies have been compared in terms of preference, but the differential effects of positive and negative reinforcement on reaction time and accuracy with other variables controlled remain unclear. Fifteen undergraduate students participated in a sound discrimination task that involved random mixed-trial presentations of positive and negative reinforcement contingencies. The participants' goal was to correctly identify whether the tone was shorter or longer than 600 milliseconds. On positive reinforcement trials, the participants received feedback and money tallies only if they identified the sound length correctly, with each correct response in the positive reinforcement trials earning the participant 10 cents. On negative reinforcement trials, the participants received feedback and money tallies only if they identified the sound length incorrectly, with incorrect trials subtracting 10 cents from the participants' total money (which began at $4.00 to equalize the weights of the positive and negative reinforcement contingencies). Accuracy analyses showed a relatively curvilinear relationship between the number of errors for each participant and the binned duration of the sound stimulus, with no differences across the positive and negative reinforcement conditions. Results also indicated weak linear negative correlations at the single subject level between comparison stimulus duration and reaction time, with similar slopes between positive and negative reinforcement trials, and strong curvilinear correlations at the group level, indicating differences between grouped and individual analyses. Overall our results appear to support abandoning the distinction between positive and negative reinforcement as two separate behavioral processes.

Sidman's (2000) theory of stimulus equivalence predicts an interaction between the development of analytic units and the development of equivalence relations. Previous research has documented these interactions (stewart, Barnes-Holmes, Roche, & Smeets, 2002; Vaidya & Brackney, 2014), therefore the current study attempted to replicate the effects seen in Vaidya & Brackney, 2014 (Experiment 2). Baseline conditional discriminations were trained for two sets of three, three-member classes, while participants simply observed stimuli in the third set which was arranged identical to those of Sets 1 and 2. Following equivalence tests where performance met the accuracy criterion of 85% for Sets 1 and 2, participants then entered a simple successive discrimination training phase where common responses were then trained with an equivalence class (pressing the Q key in the presence of A1, B1, or C1), cross equivalence classes (pressing the R key in the presence of A4, A5, or A6), or for stimuli where the participants had experience with them, but the contingencies were never arranged to facilitate equivalence class formation. Results showed a facilitative effect for common responses drawn from within equivalence classes (Set 1), and a retardation effect for common responses drawn from across equivalence classes (Set 2), for three of the five participants. Results for Set 3 showed an acquisition that fell intermediate to that of Sets 1 and 2, respectively, suggesting an interaction occurring between existing equivalence relations and the development of analytic units.

Community exercise can offer many benefits for children, including the opportunity to engage in physical activity and interact with peers in a social setting. Children with autism do not engage in as many community activities as their typical peers. This study examines conditions to teach young children to complete yoga poses to mastery. The effects of prompting, programmed reinforcers, and a chaining criteria were evaluated using a comparison design with two baselines and one intervention condition, replicated across two children with autism. Both children mastered performance of all four targeted yoga poses. The findings are discussed in the context of previous research on the benefits of yoga.

Although response effort is considered a dimension of the cost to obtain reinforcement, little research has examined the economic impact of effort on demand for food. The goal of the present study was to explore the relationship between effort and demand. Three Sprague Dawley rats were trained to press a force transducer under a series of fixed-ratio schedules (1, 10, 18, 32, 56, 100, 180, 320, and 560) under different force requirements (5.6 g and 56 g). Thus, nominal unit price (responses / food) remained constant while minimal response force requirements varied. Using a force transducer allowed the measurement of responses failing to meet the minimal force requirement (i.e. “subcriterion responses”), an advantage over prior approaches using weighted levers to manipulate effort. Consistent with prior research, increasing the unit price decreased food consumption, and raising minimum force requirements further reduced demand for food. Additionally, increasing the force requirement produced subcriterion responses. Analysis indicated that subcriterion responses did not create incidental changes in unit price. Obtained force data revealed that including obtained forces in unit price calculations provided better predictions of consumption when compared to using criterion force requirements.

Reinforcement learning occurs when organisms adapt the propensities of given behaviours on the basis of associations with reward and punishment. Currently, reinforcement learning models have been validated in minimalist environments in which only 1-2 environmental stimuli are present as possible predictors of reward. The exception to this is two studies in which the responses of the dopamine system to configurations of multiple stimuli were investigated, however, in both cases the stimuli were presented simultaneously rather than in a sequence. Therefore, we set out to understand how current models of reinforcement learning would respond under more complex conditions in which sequences of events are predictors of reward. In the two experimental chapters of this thesis, we attempted to understand whether midbrain dopaminergic neurons would respond to occasion setters (Chapter 3), and to the overexpectation effect (Chapter 4). In addition, we ran simulations of the behavioural paradigms using temporal difference models of reinforcement learning (Chapter 2) and compared the predictions of the model with the behavioural and neurophysiological data. In Chapter 3, by performing single-neuron recording from VTA and SNpc dopaminergic cells, we demonstrated that our population of neurons were most responsive to the latest predictor of reward, the conditioned stimulus (CS) and not the earliest, the occasion setter (the OS). This is in stark contrast with the predictions of the model (Chapter 2), where the greatest response is seen at the OS onset. We also showed at a neural level that there was only a weak enhancement of the response to the discriminative stimulus (SD) when this was preceded by the OS. On the other hand, at a behavioural level, bar pressing was greatest when the SD was preceded by the OS, demonstrating that rats could use the information provided by the OS, but that dopamine was not controlling the conditioned response. In Chapter 4, our population of dopaminergic neurons showed that they would preferentially respond to only one of the two conditioned stimuli (CSA, CSB) in the overexpectation paradigm. The predictions of the model (Chapter 2) suggested that when the two stimuli would be presented in compound, there would be an inhibitory response if the reward magnitude was kept constant and an excitatory response if the reward magnitude was doubled. The lack of neural firing to one of the two conditioned stimuli, however, does not make for easy interpretation of the data. Perhaps, one of the conditioned stimuli acted as if it were overshadowing the other, resulting in no response to the second CS. Interestingly, at a behavioural level, we did not see increased licking frequency to the compound stimuli presentation, a result that is somewhat at odds with the previous literature. Overall, the results of our experimental chapters suggest that the role that midbrain dopaminergic neurons play in reinforcement learning is more complex than that envisaged by previous investigations.

The present study consists of two experiments that analyze the effects of high and low densities of reinforcemnt on the maladaptive behaviors of a 9 year old girl with autism. The first experiment investigates the isolated effects of density of reinforcement on the frequency of maladaptive behaviors during a motor imitation teaching task. High densities of reinforcement produced fewer occurrences of maladaptive behavior than low densities of reinforcement. Experiment 2 analyzes the effects of density of reinforcement during the same teaching tasks as in experiment 1 on maladaptive behavior, task accuracy, prompt resistance, and language. Maladaptive behavior did not recur during experiment 2. High density of reinforcement conditions during the second experiment showed a positive effect on the accuracy of responding and compliance with prompts.

Methods for the determining the functional properties of problem behaviors are necessary for the design of successful treatments. Many of the currently utilized methodologies are chosen based on their speed, ease of application or for the perceived risk-reduction they afford. However, when thoroughly analyzed many of these methods fall short of their intended purpose. The current study attempted to assess dangerous problem behavior through a functional assessment of functionally related precursor behaviors during analog sessions. Results indicate that for three participants, placing the reinforcing contingencies on these related precursor behaviors produced differentiated outcomes during the assessment. These outcomes matched the outcomes of assessments of the more dangerous problem behaviors.