Emotional behavior trees

Abstract

Often the AI techniques for decision making used in commercial games are predictable and unadaptive. Arguably, this causes a lack of realism for the players. We believe that emotions are a vital part in the creation of interesting and believable non-player characters for games. In this paper, we present an extension to behavior trees that incorporates emotions into the decision making. Specifically, we introduce a new type of priority selector whose priorities are dynamically evaluated to allow for emotional influence. This selector takes into account timediscounting, risk perception, and planning as relevant factors of the decision making that emotions greatly influence. The objective of our work is to provide game developers with a technique to model gaming scenarios using emotional behavior trees.

A Survey of Behavior Trees in Robotics and AI

“…BTs for Game AI Type of Game Papers Real time strategy games (RTS) [38], [136], [167], [94], [65], [119], [111], [168], [120], [93] First Person Shooters (FPS) [46], [75], [71], [47], [144], [135], [17] Platform games [7], [177], [109], [129], [37], [178], [32], Dialogue games [102], [36], [133], [42], [158], [79], [34] robot. The parallel node was also discussed and expanded by [35] in combination with event driven nodes, in the context of an architecture for industrial robot control based on BTs.…”

Using String Metrics to Improve the Design of Virtual Conversational Characters: Behavior Simulator Development Study

“…Related works include Rosmalen et al [7], where an existing serious game is extended to include a chatbot, as well as those related to the formalization and use of behavior trees by Johansson and Dell'Acqua [8], Isla [9], or Imbert and de Antonio [10], where COGNITIVA is proposed as an emotional architecture for VCCs. The most closely related works to that reported here are those of Hartholt et al [5] and Morie et al [11], where the virtual human toolkit is described.…”

Towards a unified behavior trees framework for robot control

“…Unlike traditional graph theory trees [14], any node in the BT (except the Root and its only child) can have multiple parents [3]. This allows sub-trees to be reused without having to copy them but decreases readability; for this reason we explicitly advocate for the following workaround: nodes having multiple parents are prohibited, the re-usability of sub-trees is not to be done at the level of control-flow nodes, preferably, it is to be done at the level of execution nodes.…”

“…This section gives a formal description of BTs following the guidelines of [3], [8], [13]. A BT is defined as a directed acyclic graph G(V, E) with |V| nodes and |E| edges.…”