BRIGHTNESS-DISCRIMINATION ABILITIES OF CALVES RELATIVE TO THOSE OF HUMANS

Six calves and six humans were used to test their abilities to discriminate light intensities in a modified Y maze. Subjects were tested both at high brightness intensities (Experiment H) (120 lx) and low intensities (Experiment L) (3.0 lx), by comparison with a dimmer and brighter light, respectively, that gradually was advanced closer to the test intensity until a threshold was reached where discrimination was not possible. At both high and low intensities calves displayed a consistently lower correct choice rate than humans and had discrimination thresholds at 66 lx in Experiment H and 4.8 in Experiment L. Humans discriminated significantly better than calves at these intensities (P = 0.03 and P = 0.005 for Experiments H and L, respectively) and had discrimination thresholds of 105 and 4.2 lx. There were no clear differences in the relative discriminatory abilities between high or low intensities. In all tests where initial correct choice was less than 95%, calves displayed a significant increase in correct choice percentage with time. This did not occur in any test with humans.