Visual processing and top-down processing: chess pieces. Vision is perceiving electromagnetic energy: numerous possibilities, visible spectrum. Bias: colours around you are just in your head: frogs trying to camouflage into the environment red frog: secretes toxins from skin to scare away predators foraging hypothesis. Organisms that have better visual perception are better able to forage: marmoset colour perception. It has been suggested that the major advantage of trichromatic over dichromatic colour vision in primates is enhanced detection of red/yellow food items such as fruit against the dappled foliage of the forest. This hypothesis was tested by comparing the foraging ability of dichromatic and trichromatic. Geoffroy"s marmosets (callithrix geoffroyi) for orange- and green-coloured cereal balls (kix) in a naturalized captive setting. Under these conditions, trichromats but not dichromats found significantly more orange than green kix, an effect that was also evident when separately examining the data from the end of the trials, when the least conspicuous kix were left.