David Ingle

Two Visual Systems in the Frog

After unilateral removal of the optic tectum in frogs, the cut optic tract regenerates to the remaining ipsilateral tectum. Although the orienting movementselicited by moving objects (food or threats) are now directed mirror-symmetrically to normal responses, these frogs correctly localize stationary objects as barriers. Apparently, thalamic and tectal visual mechanisms can operate independently.

The effect of viewing distance upon size preference of frogs for prey

Abstract The preference of frogs for snapping at prey-like stimuli is related to real object size rather than to its subtended visual angle when objects are less than 15 cm distant. For more distant prey, the visual angle cue seems to determine prey choice. Using a second test, involving a discrimination of aperture width, behavior was guided by visual angle alone regardless of the frog to object distance. The so-called size-constancy effect may be related to feeding motivation processes, and not represent the type of perceptual judgement of real size found with human subjects.

Prey-catching behavior of anurans toward moving and stationary objects

Abstract Studies of prey-catching behavior by frogs and toads indicate that their selection of food objects is not derived directly from the visual discriminations performed by individual retinal ganglion cells. In addition to stimulus size and velocity, the distance of an object and certain “configurational” properties are important determinants of feeding activity level. When excited by odors, toads may even snap at very large objects or at stationary objects. Modifications of prey-catching behavior induced by barriers, or during visual-cliff situations provide further evidence for visuomotor flexibility among anuran amphibians.

Effects of stimulus configuration on elicited prey catching by the marine toad (Bufo marinus)

Abstract Marine toads ( Bufo marinus ) were tested for their preferences between pairs of small stimuli that were presented simultaneously on opposite sides of the body. In agreement with an earlier study of B. bufo , we found that elongation of prey along the axis of movement facilitates prey catching by B. marinus . This effect is significantly stronger for black stimuli than for white objects of the same size. Contrary to results reported for B. bufo , where double stimuli produced only inhibitory interactions, facilitation effects were found with nearby small objects. However, inhibitory effects were observed when larger stimuli were used. As a possible correlate of mutual inhibitory interactions among rival stimuli we also found via film analysis that toads strike mainly at the leading object when stimuli travel orthogonally to the toads optic axis. These various data are considered in the light of neuro-physiological interpretations.

Selective choice between double prey objects by frogs.

Frogs presented with two simultaneous andequipotent wormlike stimuli hesitated when the rival objects moved on opposite sides of the midline within the binocular visual field. Competition did not occu

Solution of a spatial constancy problem by goldfish

Goldfish readily learned to escape from a compartment by turning toward a door in the same real direction, although they approached the choice point from opposite directions on alternate trials. This ability reflects some capacity for discrimination of spatial relationships in the environment independent of a body-centered reference system.

Depth vision in monocular frogs

A test of depth discrimination ability of frogs was based upon the fact that animals will snap at prey-like objects within a sharply delimited zone but will orient to more distant objects. Following monocular blinding, frogs retained preoperative accuracy of discrimination between snapping and orienting distances.

Spontaneous shape discrimination by frogs during unconditioned escape behavior

Frogs were induced by visual threat to jump towards apertures in order to escape from a dark enclosure. These Ss consistently preferred to escape toward horizontal rather than toward vertical holes.

Enhancement by ethanol of visually evoked responses in the goldfish optic tectum

Abstract Flash-evoked potentials and multiple unit discharge were recorded from the superficial layers of the goldfish optic tectum, and post-flash histograms were prepared. When goldfish were intoxicated by a level of ethyl alcohol just sufficient to depress maze-learning ability, the first of three components of these evoked responses was consistently enhanced. These results indicate that ethanol can unbalance neural processes near the periphery as well as central brain mechanisms. Furthermore, the data provide a basis for suggestion that the retina might be useful as a model system for further physiological and pharmacological analysis of the mechanisms by which ethanol disrupts normal brain functions.

Aberrant retinotectal projections in the frog

Abstract We mapped receptive fields of isolated retinal fibers in the superficial tectum of frogs. In animals which had previously undergone partial tectal ablation, we found a normal visual map plus an overlay projection of aberrant optic fibers, instead of the compression usually reported for the gold-fish. In animals with localized mediolateral incisions in the superficial tectum, however, we found an orderly shift of the retinal projection in a lateral direction. These data seem to indicate that interactions among retinal axons can contribute substantially to reorganization of the retinal projections upon the tectum.