Did This “Study” Actually Exist?

The noted crackpot Trutherbot recently tweeted:

One study of one-million students showed people who ate a lunch without preservatives or artificial dyes scored 14% higher on IQ tests.

The original source, as far as I could tell, was an article in Psychology Today. I could not find any publication details for the study cited. Maybe it was done in an era when lead was used as a food additive. Maybe the alleged study was imaginary.