Plasticity as the Mirror of Empowerment

TL;DR

This paper introduces the concept of plasticity as a measure of how agents are influenced by observations, establishes its connection to empowerment, and discusses their fundamental trade-offs in agent design.

Contribution

It defines plasticity using a new information-theoretic measure called generalized directed information, linking it to empowerment and highlighting their dual relationship.

Findings

Plasticity is formalized as a measure of influence based on generalized directed information.

A fundamental tension between plasticity and empowerment is identified.

Plasticity and empowerment are shown to be mirror concepts with reversed influence directions.

Abstract

Agents are minimally entities that are influenced by their past observations and act to influence future observations. This latter capacity is captured by empowerment, which has served as a vital framing concept across artificial intelligence and cognitive science. This former capacity, however, is equally foundational: In what ways, and to what extent, can an agent be influenced by what it observes? In this paper, we ground this concept in a universal agent-centric measure that we refer to as plasticity, and reveal a fundamental connection to empowerment. Following a set of desiderata on a suitable definition, we define plasticity using a new information-theoretic quantity we call the generalized directed information. We show that this new quantity strictly generalizes the directed information introduced by Massey (1990) while preserving all of its desirable properties. Under this definition, we find that plasticity is well thought of as the mirror of empowerment: The two concepts are defined using the same measure, with only the direction of influence reversed. Our main result establishes a tension between the plasticity and empowerment of an agent, suggesting that agent design needs to be mindful of both characteristics. We explore the implications of these findings, and suggest that plasticity, empowerment, and their relationship are essential to understanding agency