This will be in Hour 2 of the program, in the final ten minutes. Listen on an NPR station, or online.
Here’s Herman Chernoff‘s original study [with a link to a PDF of the entire thing]:
“The Use of Faces to Represent Points in K-Dimensional Space Graphically,” Herman Chernoff, Journal of the American Statistical Association, vol. 68, no. 342, 1973, pp. 361–8.