A Comparison of Resistance to Extinction Following Dynamic and Static Schedules of Reinforcement

Resistance to extinction of single-schedule performance is negatively related to the reinforcer rate that an organism experienced in the pre-extinction context. This finding opposes the predications of behavioral momentum theory, which states that resistance to change, in general, is positively related to reinforcer rates. The quantitative model of extinction provided by behavioral momentum theory can describe resistance to extinction following single schedules in a post-hoc fashion, and only if the parameters of the model are allowed to vary considerably from those typically derived from multiple- schedule preparations. An application of the principles of Bayesian inference offers an alternative account of extinction performance following single schedules. According to the Bayesian change-detection algorithm, the temporal intervals of non-reinforcement that an organism experiences during extinction are compared to the temporal distribution of reinforcers that the organism experienced during baseline. A transition to extinction is more readily detectable when the previously collected distribution of reinforcers in timeis populated with relatively short intervals (i.e., when more frequent reinforcement was experienced during baseline). The Bayesian change-detection algorithm also suggests that changes in reinforcer rates are more detectable when organisms have temporally proximal experience with frequently changing rates. The current experiment investigated this novel prediction. Pigeons pecked keys for food under schedules of reinforcement that arranged either relatively dynamic reinforcer rates or relatively static rates across conditions. Following each period of reinforcement, resistance to extinction was assessed. Persistence was greater following static contingencies than following dynamic contingencies for the majority of subjects. These data provide support for the Bayesian approach to understanding operant extinction and might serve to extend behavioral momentum theory by offering change detection as an additional mechanism through which extinction occurs

Extension of Behavioral Momentum Theory to Conditions with Changing Reinforcer Rates

Behavioral momentum theory states that resistance to change of operant behavior is governed by the Pavlovian stimulus-reinforcer relation in a given discriminative stimulus situation. That is, higher reinforcer rates in the presence of a discriminative stimulus result in a stronger stimulus-reinforcer relation and, thereby, greater resistance to change. Within the momentum-based quantitative framework of resistance to change, the construct relating persistence to pre-disruption reinforcer rates is termed “behavioral mass.” All research on which momentum theory is based has examined resistance to change following prolonged exposure to stable reinforcer rates in multiple schedules of reinforcement. Thus, at present little is known about the time frame over which behavioral mass accumulates or the manner by which newly experienced stimulus reinforcer relations are incorporated into mass when these rates change. The experiments described in this dissertation aimed to clarify these facets of the construct. Chapters 1 and 2 provide a detailed overview behavioral momentum theory and resistance to change. Topics discussed include quantitative models of resistance to change, clinical implications of resistance-to-change research, some notable limitations of behavioral momentum theory, and extensions of the theory to account for diverse behavioral outcomes. A recently published study is presented in Chapter 3 that aimed to determine how resistance to change and behavioral mass of pigeons’ key pecking adapts in the face of stimulus-reinforcer relations that change across time during baseline. Results suggest that resistance to change is a function of recently experienced stimulus-reinforcer relations and that behavioral mass depends most heavily on these recent experiences. The experiment described in Chapter 4 extended the findings reported in Chapter 3 by examining whether behavioral mass changes during operant extinction. Pre-exposure to extinction in an alternative multiple-schedule component decreased resistance to extinction of target-component key pecking relative to conditions without pre-exposure to extinction. Between-condition differences in extinction were well accounted for quantitatively by either variation in behavioral mass or changes in the magnitude of factors that are assumed to disrupt responding during extinction. Chapter 5 offers an integrative discussion of this research and emphasizes theoretical implications, practical applications, and areas for future research

Experience with Dynamic Reinforcement Rates Decreases Resistance to Extinction

The ability of organisms to detect reinforcer-rate changes in choice preparations is positively related to two factors: the magnitude of the change in rate and the frequency with which rates change. Gallistel (2012) suggested similar rate-detection processes are responsible for decreases in responding during operant extinction. Although effects of magnitude of change in reinforcer rate on resistance to extinction are well known (e.g., the partial-reinforcement-extinction effect), effects of frequency of changes in rate prior to extinction are unknown. Thus, the present experiments examined whether frequency of changes in baseline reinforcer rates impacts resistance to extinction. Pigeons pecked keys for variable-interval food under conditions where reinforcer rates were stable and where they changed within and between sessions. Overall reinforcer rates between conditions were controlled. In Experiment 1, resistance to extinction was lower following exposure to dynamic reinforcement schedules than to static schedules. Experiment 2 showed that resistance to presession feeding, a disruptor that should not involve change-detection processes, was unaffected by baseline-schedule dynamics. These findings are consistent with the suggestion that change detection contributes to extinction. We discuss implications of change-detection processes for extinction of simple and discriminated operant behavior and relate these processes to the behavioral-momentum based approach to understanding extinction

The cichlid oral and pharyngeal jaws are evolutionarily and genetically coupled

Evolutionary constraints may significantly bias phenotypic change, while “breaking” from such constraints can lead to expanded ecological opportunity. Ray-finned fishes have broken functional constraints by developing two jaws (oral-pharyngeal), decoupling prey capture (oral jaw) from processing (pharyngeal jaw). It is hypothesized that the oral and pharyngeal jaws represent independent evolutionary modules and this facilitated diversification in feeding architectures. Here we test this hypothesis in African cichlids. Contrary to our expectation, we find integration between jaws at multiple evolutionary levels. Next, we document integration at the genetic level, and identify a candidate gene, smad7, within a pleiotropic locus for oral and pharyngeal jaw shape that exhibits correlated expression between the two tissues. Collectively, our data show that African cichlid evolutionary success has occurred within the context of a coupled jaw system, an attribute that may be driving adaptive evolution in this iconic group by facilitating rapid shifts between foraging habitats, providing an advantage in a stochastic environment such as the East African Rift-Valley

Impact of self-heating on the statistical variability in bulk and SOI FinFETs

In this paper for the first time we study the impact of self-heating on the statistical variability of bulk and SOI FinFETs designed to meet the requirements of the 14/16nm technology node. The simulations are performed using the GSS ‘atomistic’ simulator GARAND using an enhanced electro-thermal model that takes into account the impact of the fin geometry on the thermal conductivity. In the simulations we have compared the statistical variability obtained from full-scale electro-thermal simulations with the variability at uniform room temperature and at the maximum or average temperatures obtained in the electro-thermal simulations. The combined effects of line edge roughness and metal gate granularity are taken into account. The distributions and the correlations between key figures of merit including the threshold voltage, on-current, subthreshold slope and leakage current are presented and analysed

Temporal contingency

Contingency, and more particularly temporal contingency, has often figured in thinking about the nature of learning. However, it has never been formally defined in such a way as to make it a measure that can be applied to most animal learning protocols. We use elementary information theory to define contingency in such a way as to make it a measurable property of almost any conditioning protocol. We discuss how making it a measurable construct enables the exploration of the role of different contingencies in the acquisition and performance of classically and operantly conditioned behavior

Age and size at maturity: sex, environmental variability and developmental thresholds

In most organisms, transitions between different life-history stages occur later and at smaller sizes as growth conditions deteriorate. Day and Rowe recently proposed that this pattern could be explained by the existence of developmental thresholds (minimum sizes or levels of condition below which transitions are unable to proceed). The developmental-threshold model predicts that the reaction norm of age and size at maturity will rotate in an anticlockwise manner from positive to a shallow negative slope if: (i) initial body size or condition is reduced; and/or (ii) some individuals encounter poor growth conditions at increasingly early developmental stages. We tested these predictions by rearing replicated populations of soil mites Sancassania berlesei (Michael) under different growth conditions. High-food environments produced a vertical relationship between age and size at maturity. The slope became increasingly shallow as food was reduced. By contrast, high food in the maternal environment reduced the slope of the reaction norm of age and size at maturity, whereas low food increased it. Overall, the reaction norm of age and size at maturity in S. berlesei was significantly nonlinear and differed for males and females. We describe how growth conditions, mother's environment and sex determine age and size at maturity in S. berlesei