## 2 Background
### Speech in AG Design
Players need to interpret the meaning of the spoken words, in order to find the right path and pursue the game's objectives. An interactive audio story with both historical and fantasy elements can thus be shaped via monologues and/or dialogues, which are often binaurally recorded to enhance player's immersion in the audio-represented world [2; 33]. Another means for speech-facilitated mechanics is a spoken quiz, in which players are asked a question and must input the correct answer to enter the next stage [34]. Verbal output from the system to the user seems to be so well accepted that the input of voice commands has been suggested to facilitate two-way verbal interaction [35]. However, the need for sophisticated techniques to facilitate natural speech communication has been stressed [36]. Nowadays, text-to-speech (TTS) technology has been greatly advanced by artificial intelligence that employs natural language processing (NLP) technologies to mimic the human voice and provide meaningful feedback [37]. In consideration of the importance of verbal audio, the authors of this research have investigated an alternative use for speech in the context of AGs, namely its use as a raw material for the design of audio puzzles. They suggest that the implementation of spuzzles can shape new possibilities in AG experiences, since players are required to concentrate on the acoustic properties of speech, rather than only on its meaning. Speech has an intuitive impact on human psychology; it features a universal intimacy. It can thus serve as an efficient medium for training sighted players for complex audio-only interaction and potentially help them overcome their difficulty in completing challenging AG tasks. The potential of spuzzles to exercise players' listening skills is further enhanced by the educational function of games in general and puzzles in particular. The motivational power of gamification practices is widely accepted as their main benefit to the learning process [38]. However, research has recently started to focus on investigating the correlation between specific game mechanisms and learning outcomes [39]. Aligned with learning theories, such as problem solving and flow, findings have shown that challenging puzzles, even without the support of immersive elements (narratives, avatars), have a positive effect on learning both directly and via increasing engagement [40]. As a result, puzzle games have been applied to promote critical and creative thinking on a variety of topics [41; 42; 43]. To the authors' knowledge, there has been only one approach to exploring the potential of the acoustic properties of verbal information rather than its meaning. [PERSON] et al. have suggested \"spearcons\", a technique of speeding up a spoken phrase until it loses its speech recognizability, as a flexible way to sonically express menu items [44]. However, the spuzzles proposed in this paper differentiate themselves in various fundamental ways: (a) they pertain to the creation of audio puzzles rather than audio menus; (b) they can potentially employ all audio processing techniques rather than only variable playback speed; and (c) they do not eliminate the recognizability of speech, but instead retain the semantic connection with the represented information, in order to serve potential informative and narrative purposes in parallel.