Verwoerd, H. F. (1928). Effects of fatigue on the distribution of attention. Journal of Applied Psychology, 12(6), 595-601.
http://dx.doi.org/10.1037/h0071683
15 observers were required to react 15 to 25 minutes on a modification of Piorkowski's "Attention- and Fatigue-meter." Three kinds of effects of fatigue on the distribution of attention were obtained: (1) the total distribution of attention becomes less though it may remain as even as before; (2) the distribution becomes less even though the total height of performance may remain the same; (3) the range of distribution becomes narrowed though the height of performance may be maintained. The author does not recommend this method for studies involving sustained distribution of attention. (PsycINFO Database Record (c) 2016 APA, all rights reserved)