Selective attention and Pavlovian conditioning.

The present results show that the common practice of using self-indexing conditioned stimuli (CSs) in research on Pavlovian conditioning is a major source of experimental bias. The typical stimulus used is either a light flash or a sound pulse in a light/sound-shielded chamber. Under these conditions the onset characteristics of the CS signal totally predominate over the durational characteristic, i.e. the pattern information. Thus a visual pattern presented as a CS in a dark chamber is confounded with a brightness change from darkness to light. In the first experiment, animals were conditioned with a brightness CS using a self-indexing signal paradigm. When tested for specificity of the conditioning, they showed complete transfer of learning to either a visual pattern or even an auditory CS. These findings indicated that the traditional conditioning paradigm is biased towards non-specific sensory learning. The second experiment showed that specific sensory conditioning is critically dependent on selective attention mechanisms. When the onset characteristics of the CS signal were de-emphasized by the use of equal energy background illumination in the intertribal interval (ITI) during conditioning, the animals were not able to feature extract either the onset or the durational component of the CS signal from the ITI background despite prolonged training. It was only by starting with conditioning that was initially anchored to the CS onset characteristics that a perceptual fade-in procedure would bias attention to feature extract the durational characteristics of the CS. Thus conditioning occurred only when the rabbit's attention was directed to detection of the gratings display without any associated changes in visual albedo. Perhaps the most important finding of the present experiments is that the use of self-indexing CS signals in Pavlovian conditioning inevitably introduces non-specific sensory processing involving multiple sensory input pathways in the conditioning. This inherent uncertainty of the sensory input pathways presents a problem for clarifying the role of sensory pathways in the neural mechanisms of NM conditioning. In addition, the use of self-indexing CSs inevitably leads to an underestimation of the role of forebrain mechanisms in Pavlovian conditioning.

The oblique effect in the human somatic sensory system.

Blindfolded, sitting subjects were asked to feel whether two bars were parallel or not. In 50% of the presentations the bars were parallel to each other. In all presentations either one or two bars were oriented vertically, horizontally, 45 degrees or 135 degrees. In this situation the best accuracy was found when the bars were vertically and horizontally oriented in space. The experiments were repeated with the subjects tilted laterally by 45 degrees. Now the best accuracy was found when the bars were at an angle of 45 degrees or 135 degrees to the length-axis of the body. This means that the oblique effect in the somatic sensory system is of vestibular origin.

Descending pathways and the hopping response in the rabbit.

Descending pathways were studied in 5 adult rabbits by means of HRP, injected in the cervical spinal cord (in C2 and C3) at the right side. Results indicate the existence of pathways from the contralateral motor cortex, bilateral projections from the red nuclei, from the vestibular nuclei and from several nuclei in the reticular formation.

Regional cues and visual discrimination in the rabbit.

Rabbits were trained to discriminate patterns consisting of straight bars and rows of dots of different orientation. It was found that using proximal pattern presentation, at a distance of 5 cm in front of the animal, dot rows of different orientation are not discriminated on the basis of tilt extrapolation, but by the use of regional cues.

Three-dimensional retinal image stability during visual tilt discrimination in the rabbit.

Rabbits trained to discriminate vertical vs. oblique striations are unable to discriminate angular differences of 5 degrees. In the present study the instabilities around the roll axis of the eyes were measured during visual discrimination. The results indicate that these instabilities are one of the causes of the rabbit's inability to discriminate angular differences of 5 degrees.

The effects of brain lesions on the "hopping reaction" in newborn and adult rabbits: a model for studying age dependent recovery.

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 descrimination 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-development recovery was found in the visual system. In all age groups, brightness discrimination with the eye contralateral to the lesion was impaired.

Visual discrimination of discontinuous figures in the rabbit.

Rabbits were trained to discriminate between vertical and horizontal striations. After the 90% correct level had been reached transfer to vertical and horizontal rows of dots was studied. It was found that performance depended on the distance between adjacent dots. With angular dot separations (measured from the centers) larger than 4.9 degrees, performance was below the 75% correct level. This result is discussed in relation to the size of the receptive fields of orientation-selective neurons in the binocular visual cortex.

Brightness discrimination and reward strategy in the rabbit.

Two groups of rabbits were trained on a brightness discrimination task. A two-choice discrimination apparatus was used. By means of food reward one group of rabbits was trained to open the darkest gate, the other was trained to open the brightest gate. The second group learned significantly faster than the first one.

The hopping response after two-stage cortical ablation in young and adult rabbits.

In a group of 14 rabbits aged between 14 and 21 days a hemidecortication was performed in the left hemisphere. A normal monopedal lateral hopping response developed in both forelegs. At adult age, 13 weeks after the first lesion, the remaining cortex on the right side was ablated. Three days afterwards the hopping response was tested again. In all animals, the hopping response remained positive in the right foreleg, contralateral to the lesioning at early age. However, in 10 out of 14 animals the response was absent on the left side, contralateral to the recent lesion. These results show that the hopping response is not mediated by corticofugal connections of the remaining hemisphere of the foreleg contralateral to the early lesion.

The temporal retina and visual discrimination in the rabbit.

Two types of visual discrimination apparatus for rabbits can be distinguished: one in which the animal is free to move close to the targets and another in which the choice has to be made at a distance. Previously, it had been found that rabbits have a tendency to fixate the patterns with the temporal retina for visual discrimination in the first type of apparatus. The present experiments show that this is also the case in an apparatus where the rabbit discriminates at a distance.

Attenuation of neophobia and conditioned taste aversion in the rabbit.

The phenomenon of taste neophobia to apple juice does exist in the rabbit. It was found that malic acid was the main stimulus source. Attenuation of taste neophobia was due to neuronal processes which took place between rather than during drinking sessions. Conditioned taste aversion learning took place if apomorphine was injected after apple juice intake.

Binocular and monocular tiltdiscrimination in the rabbit: evidence for hemispheric dominance?

Twenty eight rabbits were trained to discriminate striated patterns of different orientation, first binocularly, than with each eye separately. There was no evidence of systematic dominance of either the left or the right hemisphere.

Interocular transfer and overtraining in the rabbit.

The possible effect of overtraining on interocular transfer of striated pattern discrimination was studied in Chinchilla rabbits. Over-training did not improve the low level of interocular transfer generally found in rabbits.

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.

Eye-closure procedure and the visual deficit after unilateral ablation of the occipital lobe in the rabbit.

In the rabbit, unilateral ablation of the occipital lobe leads to a severe impairment of striated pattern discrimination with the eye contralateral to the lesion. In the present report it is studied whether the acute reduction of the overall visual field, due to closure of the eye contralateral to the intact hemisphere shortly before each testing session, leads to results which underestimate the animal's capability to discriminate striated patterns via the ipsilateral fibres. The experiment described in the present report suggests that this is not the case and that there is a genuine visual discrimination deficit after unilateral ablation of the visual cortex.

Visual and oculomotor function in optic chiasma-sectioned rabbits.

Anatomical and physiological findings indicate that the crossed optic fibres of the rabbit have a crucial role in binocular vision. In order to directly examine the visual functions of the uncrossed fibre system, a technique of sectioning the optic chiasma midsagitally was developed. Both normal and chiasma-sectioned rabbits were tested on a variety of visual discrimination tasks as well as such oculomotor control functions as the optokinetic and vestibulo-ocular reflexes. Following transection of all contralateral retinal projections, rabbits were found to retain the same visual capacity for detection of intensity and orientation differences as before the operation. There was, however, a complete loss of optokinetic reflexes and a 50% reduction of the vestibulo-ocular reflex both in the light and in the dark.

The hopping reaction in the rabbit after early and late removal of the motor cortex.

Unilateral lesions of the sensorimotor cortex were made in rabbits either 24 h or 6 months after birth. Four months after the operation the hopping reaction in the leg contralateral to the lesion was still absent in the animals operated in adulthood. In the animals operated one day after birth a normal hopping reaction was found when tested 1.5 and 4 months after the operation.

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

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.

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

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.