The speech-to-song illusion is a robust psychological phenomenon whereby a spoken sentence sounds increasingly more musical as it is repeated. Despite decades of research, a complete formal account of this transformation is still lacking, and some of its nuanced characteristics, namely, that certain phrases appear to transform while others do not, is not well understood. Here we provide a formal account of this phenomenon, by recasting it as a statistical inference whereby a rational agent attempts to decide whether a sequence of utterances is more likely to have been produced in a song or speech. Using this approach and analyzing song and speech corpora, we further introduce a novel prose-to-lyrics illusion that is purely text-based. In this illusion, simply duplicating written sentences makes them appear more like song lyrics. We provide robust evidence for this new illusion in both human participants and large language models.

翻译：言语-歌曲幻觉是一种稳健的心理现象，即重复说出的句子会逐渐听起来更像音乐。尽管已有数十年的研究，对这一转变的完整形式化解释仍然缺失，且其某些细微特征——例如某些短语会转变而其他则不会——尚未得到充分理解。本文通过将该现象重新表述为一种统计推理，即理性主体试图判断一系列话语更可能产生于歌曲还是言语，从而为其提供了形式化解释。采用这一方法并分析歌曲与言语语料库后，我们进一步引入了一种纯文本基础的“散文-歌词幻觉”。在这种幻觉中，仅仅重复书面句子就会使它们看起来更像歌词。我们在人类参与者与大语言模型中均为此新幻觉提供了有力证据。