Extrageniculostriate vision in the monkey. II. demonstration of brightness discrimination

Five monkeys (Macaca mulatta) were trained, before and after histologically confirmed complete removal of area 17, most of 18 and part of 19, to choose the brighter of 2 targets in 3 discriminations using a pulling-in technique with movable transilluminated stimuli. A fourth test was given only postoperatively. All problems contained a 66:1 brightness difference. In test Problem I, figures differed in total luminous flux (equal area). The targets in all of the remaining tests were matched for luminous flux. In addition, in Problem III they were equated for overall surface, and in Problem IV, for amount of contour. Preoperatively, all monkeys mastered the 3 problems and showed transfer effects across the tests as revealed by both the performance of the first 10 trials, and the reduction in total error scores on successive tests. Postoperatively, all animals reached criterion level of performance in the 4 problems with significant deficits in only the first one. Marked transfer effects were present across the last 3 tests. Findings indicate that destriated monkeys may master the discrimination of targets which differ in brightness but are equated for total luminous flux and for overall surface or amount of contour. The presence of transfer effects suggests that these animals exhibited some degree of brightness constancy under the present testing conditions.