A family of reflective surfaces is presented that, when imaged by a camera, can capture a global view of the visual environment. By using these surfaces in conjunction with conventional imaging devices, it is possible to produce fields of view in excess of 180 degrees that are not affected by the distortions and aberrations found in refractive wide-angle imaging devices. By solving a differential equation expressing the camera viewing angle as a function of the angle of incidence on a reflective surface, a family of appropriate surfaces has been derived. The surfaces preserve a linear relationship between the angle of incidence of light onto the surface and the angle of reflection onto the imaging device, as does a normal mirror. However, the gradient of this linear relationship can be varied as desired to produce a larger or smaller field of view. The resulting family of surfaces has a number of applications in surveillance and machine vision.

Summary. 1. Honey bees (Apis mellifera, worker) were trained to discriminate between two random gratings oriented perpendicularly to each other. This task was quickly learned with vertical, horizontal, and oblique gratings. After being trained on perpendicularly-oriented random gratings, bees could discriminate between other perpendicularly-oriented patterns (black bars, white bars, thin lines, edges, spatial sinusoids, broken bars) as well.2. Several tests indicate that the stimuli were not discriminated on the basis of a literal image (eidetic template), but, rather, on the basis of orientation as a single parameter. An attempt to train bees to discriminate between two different random gratings oriented in the same direction was not successful, also indicating that the bees were not able to form a template of random gratings.3. Preliminary experiments with oriented 'Kanizsa rectangles' (analogue of Kanizsa triangle) suggest that edge detection in the bee may involve mechanisms similar to those that lead to the percept of illusory contours in humans.

SUMMARY1. The contrast sensitivity of the optomotor response of the fly Musca domestic was measured using a moving sinusoidal grating as the stimulus. In parallel experiments intracellular recordings were made from photoreceptors and first order visual interneurones to determine their responses to the same threshold stimuli. Measurements of the spatial modulation transfer function for photoreceptors confirm that the optics of the eye were intact during recordings.2. At the lowest intensity at which one can obtain an optomotor response, the photoreceptor signal is a train of discrete depolarizations, or bumps. With constant intensity stimuli, the temporal distribution of bumps follows the Poisson distribution with a mean rate proportional to luminance. The mean bump rate at the threshold intensity for a behavioural response is 1-7 + 0-7 sl (mean+s.D., n = 25).3. Calibrations and the statistical properties of the bump train indicate that a bump represents one effective photon, implying that the bump: photon ratios are quantum capture efficiencies.4. At low intensities the first order interneurones (the large monopolar cells or LMCs) show hyperpolarizing bumps each triggered by a receptor bump. Using a point source stimulus, centred in the field of view, the LMC bump rate is six times that in a single receptor viewing the same stimulus, as expected from the known projection of six receptor axons to each LMC. When using an extended stimulus (the grating), the bump rate is 18-20 times that in receptors. Comparison with earlier work suggests that this increased lateral summation of receptor inputs to LMCs only occurs at very low intensities.5. In both receptors and LMCs the amplitudes and wave forms of bumps depend upon the position of a point source stimulus within the field of view. With the light in the periphery of the field the bumps are smaller and slower than when the light is in the centre. This difference in response suggests that spatial summation is brought about by lateral interactions, possibly between receptors.6. At higher mean intensities the signal-to-noise ratios in receptors responding to the appropriate threshold stimuli increase with intensity. This is suggestive of a decrease in the extent of spatial and/or temporal summation in the optomotor pathway.

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Animal camouflage patterns may exploit, and thus give an insight into, visual processing mechanisms. In one common type of camouflage the borders of the coloured patterns are enhanced by high contrast lines. This type of camouflage is seen on many frogs and we use it as the basis for speculating about vision in a small, frog-eating snake. It is argued that a simple categorization of intensity profiles, such as that invoked by a mechanism that detects phase-congruence, occurs at an early stage of snake vision. We show that edge-detectors using a phase-congruence strategy will be unable to distinguish between 'natural' step-edges and the enhanced border profiles commonly seen on cryptic animals, and that the camouflage will be effective over a wide range of spatial scales.