The CIE 1964 standard observer is based on the mean 10-deg color matching functions of Stiles & Burch (1959) and of Speranskaya (1959). In averaging the functions together, the Speranskaya were given a low weight, particularly at the spectral extremes, so that the final functions are dominated by those of Stiles & Burch.
From Table I(3.3.2) of Wyszecki & Stiles (1982).
The 10-deg CMFs reflect a lower macular pigment density than the 2-deg functions, since macular pigmentation declines with eccentricity. They also reflect a narrowing of the underlying cone spectral sensitivities, since cones become shorter and broader with increasing eccentricity, thus reducing the axial optical pigment density in the cone outer segment.
CIE Proceedings (1964) Vienna Session, 1963, Vol. B, pp. 209-220 (Committee Report E-1.4.1), Bureau Central de la CIE, Paris
Speranskaya, N. I. (1959). Determination of spectrum color co-ordinates for twenty-seven normal observers. Optics and Spectroscopy, 7, 424-428.
Stiles, W. S., & Burch, J. M. (1959). NPL colour-matching investigation: Final report. Optica Acta, 6, 1-26.
Wyszecki, G., & Stiles, W. S. (1982). Color Science: concepts and methods, quantitative data and formulae. (2nd ed.). New York: Wiley.