Broschiertes Buch

HOW DO BEES (AND HUMANS) SEE GREY LEVELS?

Intuitive, logical, and anti-intuitive explanations for some curious observations

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There are several sources of serious confusion in the investigations of how bees and humans see grey and black. First, von Frisch trained bees to go to a coloured paper, and then tested whether they could distinguish that colour from a palette of 15 shades of grey placed together on a test board. Unfortunately, he used papers made from wood pulp, which do not reflect ultraviolet, so the UV receptors were excluded. Secondly,16 years later it was shown that bees require a 25% difference in brightness to discriminate grey levels, so his test was uncertain. Thirdly, bees are dichromats, and detect only green contrast and the fraction of light that stimulates the blue receptors. The most interesting confusion is that grey photons do not exist, but that does not affect bees because they are functional dichromats and treat grey like any other colour. No problem. The UV receptors in the compound eyes of the bee are used to detect the direction of the sky to stabilize flight and escape upwards when disturbed. The bee is a sexless herbivore, which may account for its relatively simple retina. Additional colour types of receptor have been found by recording from eyes of some flies, butterflies and dragonflies, presumably for unique recognition of the other sex or prey. However, this is one-purpose vision which does not require much processing or large brain. Full colour vision requires at least three colour types of receptors and a large visual cortex, as in primates. Human vision is more difficult to understand in this context. Black is entirely a hallucination because there are no black photons. White is detected normally with three receptor types acting together, but the brightest objects in sight also look white even though they are green or red, maybe as a calibration. The edges of shiny objects also look white although clearly they are not. Grey is hallucinated as various levels of black where there is white but insufficient illumination to see it as white.These topics are discussed in historical context. However, some who work on the vision of the bee still believe that bees have full colour vision, and many believe that their dog or cat sees only black and white, so called achromatic vision. However, like the bee, they all evolved in world where green predominated, and many things of interest were less blue (e.g., yellow) or more blue than green (e.g., blue), so most mammals evolved as dichromats, without UV or red receptors.

Weniger Details

Born 1927, after wartime schooling, then 4 years as a scholar at St John's College, Cambridge, Adrian spent 10 years working out details of nervous systems and nervous control of movement in the phylum Coelenterata, including jellyfish, medusae, and corals, and also Ctenophores. There followed a year at the Center for Study of the Behavioral Sciences at Palo Alto, with Ted Bullock, writing a huge two-volume work on Invertebrate Nervous Systems (1965).When Adrian returned to St. Andrews, Scotland, he had decided to concentrate on all aspects of the arthropod compound eye. His first students recorded from the photoreceptors, and described the basic optics of the locust and fly eyes and their capture of single photons at extremely low light levels. He subsequently published about 250 papers on the compound and optic lobes of many kinds of insects. In 1969 he was elected to the Royal Society and in that year became one of four Founder Professors of Biological Sciences in the Australian National University where the work on insect vision continued. In 1990, discoveries of how insects pilot themselves in flight, together with his early experience working at Farnborough, led to applications in drone helicopters and planes, with computer and vision on board, supported by American funds. For more detail, see his web page at Adrian-Horridge.orgAdrian retired in 1992 and turned to the analysis of what bees see, by using a Y-choice maze. This analysis led to the discovery of feature detectors for combinations of edges, circles and spokes in one channel for green contrast at edges, and for content and height of blue in a separate channel. Left/right polarity between an area of blue and of green contrast was also detected, learned, and used as a signpost. The UV receptor in each ommatidia seems to be used only for registering the direction of the sky as an escape route. Hundreds of hours training bees and testing them for what they had learned led to a book "The Discovery of a Visual System: The Honeybee" (2019). Adrian is also known for his books and papers which record the lost maritime ethnology of Indonesia. In the 1970's and 80's he made a unique photographic record of many local types on many distant islands. That World Heritage fleet of thousands of fishing boats and outrigger canoes has now become motorised, designs changed, and rigging gone. There is little improvement in the catch because there was always overfishing and depletion, and now there is carbon dioxide emission from the engines.