![]() ![]() These are the green receptor intensity the blue receptor intensity, called tonic responses and also the respective changes (modulation) of intensity at each of these receptors, called phasic responses. ![]() Therefore, with UV excluded from the experiments, there are four independent inputs at each local region of the eye that could respond to a white, gray, or colored pattern. The bees measured modulations of the blue and green receptors separately 10 and recognized them only in the positions where they had been learned on the retina. 9 They showed no evidence that patterns or shapes were reassembled, and plenty to show that they did not. They detected edge orientation and radial and circular edges as components of patterns. In previous work with black/white patterns, bees discriminated mainly by the modulation of the green receptor pathway. Note: Insets – the targets seen from behind, showing the support legs and the reward box behind one of them. The two targets, together with the reward, change sides every 5 minutes. The criterion for success is when the bee passes over one of the transparent baffles. The bees fly in at the front and make a choice at a fixed distance from the two targets. This Y-choice apparatus was used in all the experiments. Even more curious, a black/white edge was not distinguished from a white/black edge, 8 which suggests that the edge detectors are symmetrical. Earlier tests of trained bees in the apparatus showed that the positions of the black or gray panels were located very well in the vertical direction, but poorly along the horizontal, 7 despite the abundant contrast at the vertical edges. In return for a reward of sugar solution, bees readily learn to come to the “choice” chamber where they can choose between the patterns or colors displayed on two targets ( Figure 1). In brief, the spatial and temporal properties of the peripheral neurons are optimized to detect moving stimuli and edges, 6 not areas of black, white, or color. 5 Bees detect changes of intensity caused by scanning across edges. 5 The responses of the photoreceptors, and particularly of the second-order neurons, are rapidly changing potentials (phasic responses), called modulations. Electrophysiology shows that the responses to steady illumination adapt rapidly. However, the rapid changes of sensitivity over a 1,000-fold range seen with changes of light intensity, 4 make it unlikely that the bee’s discrimination of gray, white, or color is based simply on the ratios of the intensities at the receptors.Ī good deal is already known about the peripheral neural input pathways. All three receptor types respond to white and shades of gray, including UV, and the bee’s preferences for colors are indifferent to sunlight or shade. 2, 3 However, the strength of the stimulus at each receptor type tells nothing about the subsequent neural processing. The three types of photoreceptors of the bee compound eye have spectral sensitivity peaks in the green, blue, and ultraviolet (UV) wavelengths, 1 so it has usually been accepted that color is detected from the interaction of the responses in these three channels. There has been much interest in how bees detect the shapes and colors of flowers and of landmarks by which they recognize places, but the way that they distinguish between black and white appears to have been overlooked. These findings provide a small step toward understanding, modeling, and implementing in silicon the anti-intuitive visual system of the honeybee, in feeding behavior. These two inputs were sufficient to help decide which of two targets held the reward of sugar solution, but the bees cared nothing for the black or white as colors, or the direction of contrast at black/white edges. They also learned the average position and total amount of blue reflected from white areas. The first input was the position and a measure of the green receptor modulation at the vertical edges of a black area, which included a measure of the angular width between the edges of black. As revealed by extensive tests of trained bees, bees learned two strong signals displayed on either target. Bees have quite different and accessible mechanisms. Human vision sidesteps the issue by constructing black and white in the brain. With ultraviolet reflections excluded by the apparatus, bees can learn to distinguish between black, gray, and white, but theories of color vision are clearly of no help in explaining how they succeed. ![]() Bee eyes have photoreceptors for ultraviolet, green, and blue wavelengths that are excited by reflected white but not by black. ![]()
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