Hi again, Gary
The study comparing EEG patterns in yogis and Zen meditators is in Charles Tart’s *Altered States of Consciousness* (NY: John Wiley & Sons, Inc., 1969), pp. 489-506.
I had a hunch and, lo and behold, I found this reference cited in P. Kapleau’s *Zen: Dawn in the West* (Doubleday Anchor, 1980), p. 272.
Hope this helps,
Katherine Masis