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T Collett

Publications and source records attributed to T Collett.

14 recordsLinked to original sources
PubMed1996

Insect navigation en route to the goal: multiple strategies for the use of landmarks

There are at least four distinct ways in which familiar landmarks aid an insect on its trips between nest and foraging site. Recognising scenes: when bees are displaced unexpectedly from their hive to one of several familiar locations, they are able to head in the direction of home as though they had previously linked an appropriate directional vector to a view of the scene at the release site. Biased detours: ants recognise familiar landmarks en route and will correct their path by steering consistently to the left or to the right around them. Aiming at beacons: bees and ants also guide their path by approaching familiar landmarks lying on or close to the direct line between start and finish. Simulations suggest that such mechanisms acting together may suffice to account for the routes taken by desert ants through a landmark-strewn environment: the stereotyped trajectories of individual ants can be modelled by a weighted combination of dead reckoning, biased detours and beacon-aiming. These mechanisms guide an insect sufficiently close to an inconspicuous goal for image matching to be successfully employed to locate it. Insects then move until their current retinal image matches a stored view of the surrounding panorama seen from a vantage point close to the goal. Bees and wasps perform learning flights on their first departure from a site to which they will return. These flights seem to be designed to pick up the information needed for several navigational strategies. Thus, a large portion of the learning flight of a bee leaving a feeder tends to be spent close to the feeder so aiding the acquisition of a view from that vantage point, as is needed for image matching. Bees and social wasps also tend to inspect their surroundings while facing along preferred directions and to adopt similar bearings before landing, thereby making it easy to employ retinotopically stored patterns in image matching. Aiming at beacons, in contrast, requires a landmark to be familiar to the frontal retina. Objects tend to be viewed frontally while the insect circles through arcs centred on the goal. This procedure may help insects to pick out those objects close to the goal that are best suited for guiding later returns.

Journal Article↗
PubMed1996

Honeybee navigation en route to the goal: visual flight control and odometry

Recent research has uncovered a number of different ways in which bees use cues derived from optic flow for navigational purposes. The distance flown to a food source is gauged by integrating the apparent motion of the visual world that is experienced en route. In other words, bees possess a visually driven 'odometer' that is robust to variations in wind load and energy expenditure. Bees flying through a tunnel maintain equidistance to the flanking walls by balancing the apparent speeds of the images of the walls. This strategy enables them to negotiate narrow passages or to fly between obstacles. The speed of flight in a tunnel is controlled by holding constant the average image velocity as seen by the two eyes. This avoids potential collisions by ensuring that the bee slows down when flying through narrow passages. Bees landing on a horizontal surface hold constant the image velocity of the surface as they approach it. This automatically ensures that flight speed decreases with altitude and is close to zero at touchdown. The movement-sensitive mechanisms underlying these various behaviours seem to be different, qualitatively as well as quantitatively, from those mediating the well-investigated optomotor response.

Journal Article↗
PubMed1996

Magnetic compass cues and visual pattern learning in honeybees

We show that honeybees can learn to distinguish between two 360 ° panoramic patterns that are identical except for their compass orientation; in this case, the difference was a 90 ° rotation about the vertical axis. To solve this task, bees must learn the patterns with respect to a directional framework. The most powerful cue to direction comes from the sky, but discrimination between patterns is possible in the absence of celestial information. Under some conditions, when other potential directional cues have been disrupted, we show that bees can use a magnetic direction to discriminate between the patterns.

Journal Article↗
PubMed1995

Convergent processing in honeybee vision: multiple channels for the recognition of shape.

Advanced mammalian visual systems can recognize a familiar shape under a variety of viewing conditions. Recognition is possible whether the shape is presented in simple outline, as a random dot stereogram, or by motion contrast. We report here that bees have a similar ability: they can recognize a shape when it is learned through visual signals of one kind and subsequently viewed through another. The results reveal that (i) bees that have learned a shape defined in terms of luminance contrast can recognize the same shape when it is defined in terms of motion contrast, (ii) shapes that are delineated by motion contrast are discriminated through a channel that receives input only from the green photoreceptors, (iii) a shape learned through one class of signal is subsequently recognized via any of these other classes, and (iv) shape is memorized in a generic form regardless of whether it is initially sensed by green-contrast, blue-contrast, luminance-contrast, or motion-contrast signals.

Journal Article↗
PubMed1994

Lower-field myopia and astigmatism in amphibians and chickens.

In some afoveate vertebrates refractive state appears to vary over the eye to match the average viewing distances of different areas of the visual field. However, precise measurements are difficult to obtain even in anesthetized animals, because standard methods of refraction are not designed for off-axis measurements and because the presence of astigmatism may fog the results. Therefore we developed a new automated objective technique, automated infrared photoretinoscopy, and measured off-axis refractions in alert chickens and amphibians. We found, in agreement with previous studies, that chickens (Gallus domesticus) are myopic and also have some astigmatism in the lower visual field. Lower-field myopia was, however, variable. It did not match the distance to the ground precisely, but it declined with age (as increased head height would predict). With-the-rule astigmatism was noticed in early posthatching development; it was striking even along the optic axis. The astigmatism lessened with age, as it does in human infants. Frogs (Rana pipiens and Rana temporaria) displayed pronounced myopic astigmatism that was confined to the lower visual field. Salamanders (Salamandra salamandra) and toads (Bufo bufo) showed less variation in refractive state across the visual field, although toads also were myopic in the lower visual field.

Animals↗
PubMed1992

Vertical disparity and binocular vision in the praying mantis.

We have investigated how the binocular control of prey capture in the praying mantis is affected by abnormally large vertical disparities, which were introduced by prisms placed in front of the eyes. The position of a target on the two retinae determines both the magnitude of head saccades made to fixate a target and its perceived distance. Over the whole range of vertical disparities tested (up to at least 30 deg), the frequency of fixating saccades is normal while the amplitude of their vertical component is a compromise between the saccades specified by each eye individually. Distance measurements are not affected by imposed vertical disparities. But the larger the vertical disparity, the more reluctant the mantid is to strike at the target until disparities exceed 15 deg when no strikes are elicited at all.

Animals↗
PubMed1977

Stereopsis in toads.

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Accommodation, Ocular↗