Utah State University
Project Title: Unveiling the Mechanisms of Choice Between Multiple Alternatives
In a broad sense, choice refers to how organisms distribute the limited amount of time they have available among all possible alternatives. Richard Herrnstein famously argued that, under this definition, all behavior constitutes choice. His argument rested on the notion that no matter how impoverished an organism’s environment might be, there will always be more than one alternative to engage in. For instance, a rat pressing a lever for food in an operant chamber might occasionally stop to groom, roam around, or even sleep. The study of choice under this framework led to matching theory, which in turn produced a gargantuan body of research throughout the years. Matching theory, and specifically the matching law, attempts to predict how much time an organism will allocate to one particular behavior as a function of the proportion of all reinforcers that this behavior produces. This is a significant achievement for behavior analysis, but several questions still remain: why do organisms behave according to the matching law? What prompts an animal to disengage from the activity they are currently emitting to do something else? Matias Avellaneda sought to develop a mathematical model that would shed light on these matters. To this end, he built on previous research showing that the distribution of visit durations in concurrent schedules of reinforcement is approximately exponential, which implies that concurrent-schedule performance can be modeled using continuous-time Markov chains. He also refined equations originally proposed by Randy Gallistel and colleagues, which resulted in a successful model of visit duration in two-alternative choice. In the dissertation research proposed for the 2025 Innovative Student Research Grant, Matias showed that different assumptions about which mechanisms underlie the decision to abandon an alternative to engage with another one result in different extensions of his model when more than two alternatives are considered. Using these extensions, he designed a critical experiment whose results will support at most one of the extensions, thus showing which of the posited mechanisms (if any) are plausible. The supported model would provide tentative but feasible answers to the questions raised above, thus greatly improving our understanding of choice.
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