Investigating the impact of platformer game levels on game
character believability
Student: Ms Elizabeth Camilleri,
Supervisor: Prof Alexiei Dingli; Co-supervisor: Prof Georgios N Yannakakis
Introduction
Game character believability is a subjective concept for which no official definition or
method of measurement exists at the time of writing. However, it is commonly viewed as
the ability of a game character to convince human observers that it is being controlled by a
human player. It is often assumed that game character believability is dependent on the
algorithm controlling the character’s behaviour. However, it has been speculated that it may
also be influenced by the game level within which the character acts [1].
Project Objectives
The aim of this study is to determine whether and to what extent game levels indeed
influence the believability of game characters within them. The following objectives were
set: to obtain a number of video clips of levels varying in design played by players varying in
believability, to obtain a believability measure for them via crowdsourcing and to use these
to model the effect of level and gameplay parameters on believability.
Project Methodologies
A number of levels for the test-bed game (largely based on Infinite Mario Bros [2] and
SuperTux [3]) were generated with varied level parameter values. Four players (two humans
and two artificial agents) played through these levels and video clips were recorded for each
playthrough. An online questionnaire was constructed where subjects viewed these clips in
pairs and indicated which character in each video clip pair they perceived as more
believable. These preference pairs were then fed into a Preference Learning algorithm to
infer a hypothetical model of the relationship between the level and gameplay parameters
and the reported believability preferences.
Results and Achievements
Using different algorithms, parameters and preference pair subsets with the Preference
Learning module, the relationship was modelled with an accuracy of 72.83%. Through
several tests and analyses, game level parameters were shown to have a strong yet indirect
effect on the reported believability preferences. In particular, the number of gaps and
enemies in the level seem to have a positive impact. These results shed light on a niche
research area in Game AI and further work on this study opens up the possibility of
optimising game character believability using level parameters.
References
[1] J. Togelius, G. Yannakakis, S. Karakovskiy, and N. Shaker, “Assessing believability," in
Believable Bots, P. Hingston, Ed. Springer Berlin Heidelberg, 2012, pp. 215-230. [Online].
Available: http://dx.doi.org/10.1007/978-3-642-32323-2 9
[2] “Infinite Mario Bros.” [Online]. Available:
http://www.mariogames.be/Infinite_Mario_Bros_Game
[3] “SuperTux.” [Online]. Available: http://www.supertux.lethargik.org/
Figure 1 - A system diagram. Game image assets source: [3]
Figure 2 – A screenshot of the online questionnaire used to obtain the believability preference pairs. Game image assets
source: [3]