The preprint of our singing intonation paper is now available! Enjoy!
[Edit: now published here]

Abstract:
This paper presents a study on intonation and intonation drift in unaccompanied singing and proposes a simple model of reference pitch memory that accounts for many of the effects observed. Singing experiments were conducted with 24 singers of varying ability under 3 conditions (Normal, Masked, Imagined). Over the duration of a recording, approximately 50 seconds, a median absolute intonation drift of 11 cents was observed. While smaller than the median note error (19 cents), drift was significant in 22% of recordings. Drift magnitude did not correlate with other measures of singing accuracy, singing experience or with the presence of conditions tested. Furthermore, it is shown that neither a static intonation memory model nor a memoryless interval-based intonation model can account for the accuracy and drift behaviour observed. The proposed causal model provides a better explanation as it treats the reference pitch as a changing latent variable.

Disclaimer:
This article has been accepted by the Journal of the Acoustical Society of America, JASA. After it is published, it will be found at http://scitation.aip.org/JASA.
[Edit: now published here]