# The active time model of concurrent choice

## TL;DR

This paper introduces a new model called the active time model to explain how animals make choices in concurrent reinforcement schedules.

## Contribution

The active time model offers a novel approach to concurrent choice by focusing on the time since the last response as the controlling stimulus.

## Key findings

- The active time model successfully accounts for multiple data sets in concurrent variable-interval schedules.
- The model outperforms other existing models like melioration and scalar expectancy theory in explaining choice patterns.
- The paper concludes that operant choice is influenced by multiple factors and should be viewed adaptively.

## Abstract

The following paper describes a steady-state model of concurrent choice, termed the active time model (ATM). ATM is derived from maximization principles and is characterized by a semi-Markov process. The model proposes that the controlling stimulus in concurrent variable-interval (VI) VI schedules of reinforcement is the time interval since the most recent response, termed here “the active interresponse time” or simply “active time.” In the model after a response is generated, it is categorized by a function that relates active times to switch/stay probabilities. In the paper the output of ATM is compared with predictions made by three other models of operant conditioning: melioration, a version of scalar expectancy theory (SET), and momentary maximization. Data sets considered include preferences in multiple-concurrent VI VI schedules, molecular choice patterns, correlations between switching and perseveration, and molar choice proportions. It is shown that ATM can account for all of these data sets, while the other models produce more limited fits. However, rather than argue that ATM is the singular model for concurrent VI VI choice, a consideration of its concept space leads to the conclusion that operant choice is multiply-determined, and that an adaptive viewpoint–one that considers experimental procedures both as selecting mechanisms for animal choice as well as tests of the controlling variables of that choice–is warranted.