Stiles' p mechanisms


Figure 3.11.23 from Stockman, A., & Brainard, D. H. (2009). Color vision mechanisms. In M. Bass, C. DeCusatis, J. Enoch, V. Lakshminarayanan, G. Li, C. Macdonald, V. Mahajan & E. van Stryland (Eds.), The Optical Society of America Handbook of Optics, 3rd edition, Volume III: Vision and Vision Optics. New York: McGraw Hill.


Stiles’ π-mechanisms. Field spectral sensitivities of the seven π mechanisms: π1  (purple triangles),  π2  (dark blue inverted triangles),  π3 (light blue circles),  π4  (green diamonds),  π'4  (green half-filled diamonds),  π5  (red squares),  π'5 (red half-filled squares). The field sensitivities are the reciprocals of the field radiances (in log quanta s-1 deg-2) required to raise the threshold of each "isolated" π-mechanism by one log unit above its absolute threshold. The results were averaged across four subjects: three females aged 20-30 and one male aged 51. Details of the experimental conditions can be found on p.12 of Stiles' book (Stiles, 1978). Data from Table 2(7.4.3) of Wyszecki & Stiles (1982).


Stiles, W. S. (1978). Mechanisms of Colour Vision. London: Academic Press.

Wyszecki, G., & Stiles, W. S. (1982). Color Science: concepts and methods, quantitative data and formulae (2nd ed.). New York: Wiley.