Confusion errors in monkey short-term memory

Gave short-term memory tests to 9 highly trained rhesus monkeys in a pattern reproduction paradigm. A red and a white light in a 4 * 4 matrix were illuminated for .20 sec. After a predetermined delay, ss were required to open the door to the cell which previously had been illuminated with a white light. With a constant 5-sec delay, responses to the incorrect red light decreased steadily with practice but remained substantially above chance after 20 days (960 trials) of practice. The pattern of errors with 0-, 2-, and 5-sec delays supports the hypothesis that ss sometimes fail to perceive or encode the red-lighted cells differently from those lighted white. (PsycINFO Database Record (c) 2006 APA, all rights reserved).