M.W. Van Hof

Discrimination between striated patterns of different orientation in the rabbit

Abstract Discrimination between striations of different orientation was studied in the rabbit. Discrimination between striations at 45° and 135° to the horizontal was found to be as readily performed as that between vertical vs. horizontal striations. It was shown that this discrimination is not due to the overall pattern formed by the two patterns together, but a combination of a positive reaction to the rewarded pattern and a negative reaction to the unrewarded pattern. Discrimination was performed equally well after covering one eye.

Visual acuity in the rabbit

Abstract Rabbits were trained to discriminate vertical and horizontal striations. By changing the width of the white and black bars, visual acuity was studied. Four animals were studied. In three of them the finest pattern that could be discriminated was that in which the bars were seen under a 20′ visual angle. The fourth animal was able to discriminate bars of 10′ visual angle.

The angular threshold of discrimination for striated patterns of different orientation in the rabbit

Abstract The angular threshold of discrimination between striated patterns of different orientation was studied in three rabbits. In each animal this threshold was determined for orientations around three different axes: vertical, horizontal and 45°. In all three animals studied the threshold value around the vertical as well as the horizontal axis was between 5° and 10°. In one rabbit the threshold around the 45° axis lay also between these values, but in the other two it was between 10° and 15°. An interpolation procedure indicates that the difference between discrimination angles is maximally 4°.

Visual discrimination after bilateral removal of the visual cortex in the rabbit

Rabbits were trained on a brightness and a vertical vs horizontal discrimination. After bilateral removal of the visual cortex the threshold of brightness discrimination was significantly higher. In addition, there was a severe impairment of striated pattern discrimination.

Motor behaviour and visual discrimination after neonatal and adult hemidecortication in the rabbit

In 5 groups of rabbits (0-1, 2-3, 4-5, 6-7 and 12-13 weeks old) the left frontal, parieto-temporal and occipital cortex were removed. Beginning two weeks after the operations the hopping reaction was tested during 15 weeks. It was found in the groups operated 0-1, 2-3 and 4-5 weeks after birth, that the hopping reaction developed normally. This was not the case in the animals operated 6-7 and 12-13 weeks after birth. Brightness discrimination with the left and right eye was tested in the same animals, beginning 12 weeks after the operation. Contrary to the motor system, no age-dependent recovery was found in the visual system. In all age groups, brightness discrimination with the eye contralateral to the lesion was impaired.

Angular acuity in normal and commissure-sectioned rabbits

Both normal and commissure-sectioned rabbits were examined over a variety of visual discrimination tasks. The visual displays were projected at various distances within the frontal visual field of the rabbit. The learning of either a black-white or a vertical-horizontal problem was found to be normal in commissure-cut animals. Furthermore, no deficit in angular acuity was observed. However, when they were tested with the patterns displayed at 25 cm distance, large impairments were found in the commissure-sectioned animals.

Residual visuomotor behaviour after bilateral removal of the occipital lobe in the rabbit.

Abstract After bilateral removal of the occipital lobe rabbits were studied in an enriched environment. At first their behaviour was severely impaired. After eight weeks the animals had learned to avoid obstacles, climb up ramps and jump from tables. It was shown that this recovery was due to the use of remaining visual structures. For this the pressure of an enriched environment was essential. In spite of this recovery the animals were incapable of striated pattern discrimination. Although black-white discrimination was apparently normal, the brightness threshold was found to be increased.

The contribution of the rewarded and unrewarded stimulus in two-choice pattern discrimination after a unilateral ablation of the occipital lobe in the rabbit

Abstract The contribution of the rewarded and unrewarded stimulus in two-choice pattern discrimination after a unilateral ablation of the occipital lobe was studied in 14 rabbits. With the eye contralateral to the intact hemisphere the correct decision is mainly based on avoidance of the unrewarded stimulus. The results with the eye contralateral to the lesion suggest that both the unrewarded and rewarded stimulus play a role in the decision.

The contribution of the rewarded and unrewarded stimulus in two-choice pattern discrimination in the rabbit

Abstract Rabbits were trained to discriminate vertical vs horizontal striations. After reaching criterion one of the patterns was randomly replaced by striations oriented at 135°. Other rabbits were trained to discriminate 45° vs 135° striations. After reaching criterion, one of the patterns was randomly replaced by vertical or horizontal striations. It was found that performance remained at the 90% correct level when the unrewarded pattern was present. When this was not the case performance dropped to 60–70% correct. It was concluded that in the discrimination apparatus used in this study, the rabbits choice is mainly controlled by the unrewarded stimulus.

Visual discrimination after early and late unilateral enucleation of the rabbit

Brightness and tilt discrimination were studied in rabbits in which one eye had been enucleated either 1 day or 3 months after birth. When tested at the age of 5 months no differences in performance were found between both groups of animals.