Birds have excellent spatial acuity and colour vision compared to other vertebrates while spatial contrast sensitivity is relatively poor for unknown reasons. Contrast sensitivity describes the detection of gratings of varying spatial frequency. It is unclear whether bird brightness discrimination between large uniform fields is poor as well. Here we show that budgerigars (Melopsittacus undulat...

Underwater, the contrast between object and background is much larger reduced with increasing distance between object and observer than in air. For marine predators, such as pinnipeds, it would therefore be advantageous to possess a high sensitivity for brightness differences, since this would increase the distance at which prey can be detected visually. Few studies have examined the brightness...

background one of the main objects in medical science is diagnosis the diseases and classification the patients to different classes. consequently according to the above the patients that set in one classes should have maximum similarity with each other. discrimination and classification analysis have been frequently used in medical data for diagnosis and prognostic of the disease. the wrong in...