My Library

Meanwhile, the experimental workload had quadrupled, largely to my own demands and interests. There were the "ESPateacher" experiments utilizing the equipment designed by Jim Merriweather, and which he kept improving on. There were Dr. Silfen's "flicker fusion" experiments, and an interesting set of her experiments referred to as "brightness comparator" experiments. A great deal was learned from the brightness comparator experiments. Since the yield from these particular experiments was eventually to play a seminal role in the work at SRI, I'll briefly review them. As I remember the brightness comparator equipment, it consisted of a big black box whose open end was some kind of photo-projection screen. Upon the screen various shapes could be projected in a back-lit fashion and the light intensity of the targets could be adjusted so that they could be dim, medium strong, and very strongly lit. The targets themselves were painted with phosphorus, the kind which glows in "dark light" in the ultraviolet band of the spectrum. The intensity of the ultraviolet light could be modulated by a rheostat device. Whether the target was strongly lit or dim, it was indicated by a slightly illuminated circle. The successive experiments were run for twenty or more trials before the subject received any feedback as to "hit" or "miss."