The paper “Mathematical Analysis of Light-sensitivity Related Challenges in Assessment of the Intrinsic Period of the Human Circadian Pacemaker“, co-authored by Imran Usmani, Derk-Jan Dijk (Surrey Sleep Research Centre), and Anne Skeldon, has been published in the Journal of Biological Rhythms (open access link at the journal). This paper is based on Imran’s PhD thesis at Surrey. Imran was jointly supervised by Anne and Derk-Jan and successfully defended his thesis in 2022. Mathematically, the paper shows that the gold-standard method for measuring the period of the human biological clock may not be the “true” period. This is quite a controversial idea but could explain observed differences between sighted and blind people. A followup letter to the editor by M.A. St Hilaire, C.A. Czeisler, and E.B. Klerman (link here) raised questions about some of the results in the above paper, and a followup rebuttal by Skeldon et al (link here) has also been published in the same journal. The image below is Figure 1 from the paper.