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E Vandenbussche

Publications and source records attributed to E Vandenbussche.

16 recordsLinked to original sources
PubMed1992

Texture segregation in the cat: a parametric study.

We have investigated how different texture parameters affect texture segregation in the cat, and which strategies cats use to solve the segregation task. Five cats were presented with stimuli consisting of two adjacent panels. One side contained a square area of a particular texture embedded in a different background texture; the other side was filled with only the background texture. The animal's task was to detect at which side the texture difference was presented. Sensitivity for the texture difference was assessed by making one aspect of the texture (in most instances the size of the texture elements) dependent upon performance by means of a staircase procedure. Among the most prominent parametric effects are those of density and element position randomization. In general, segregation was optimal at intermediate densities and deteriorated at larger and smaller densities. Element position randomization caused a slight but systematic decrease in segregation performance. Furthermore, we found texture elements at the border between different textures to be of primary importance for segregation. Which strategy the animals used for solving the segregation task depended upon the presence of random figure/background reversals in subsequent stimulus presentations during training. The animals learned to detect texture differences if these reversals were present, and without reversals, they learned to identify the particular texture in the target square. Interestingly, parameter dependencies of segregation did not depend upon the detection strategy used. We have speculated that the two different strategies used by the cats to solve the segregation tasks are related to different hierarchical levels of texture segregation which can be traced back to different stages of texture processing in human models of segregation performance.

Animals↗
PubMed1991

Orientation discrimination in the cat: its cortical locus. I. Areas 17 and 18.

An elementary unit of visual pattern and form perception is thought to be the orientation of edges; this element has been studied extensively by neurophysiologists using oriented line segments or bars. These same stimuli have been used in the present study to measure threshold discriminations in cats before and after cortical lesions of areas 17 and/or 18. Control experiments showed that the discriminations were made by using a single cue, orientation, and that other stimulus parameters, width, length and contrast of the bar, were optimized. The extent of the lesions was evaluated anatomically from cell and fiber stained sections through cortex and thalamus, matched to retinotopic maps of Tusa et al. (Cortical Sensory Organization, Vol. 2, Humana Press, pp. 1-31, '81) and Sanderson (Journal of Comparative Neurology 143:101-118, '71), and physiologically from visual field position of receptive fields of cells recorded in areas neighboring the lesions. Lesions involving area 17 and large parts of area 18 produced a marked deficit in orientation discrimination which included a loss in retention, and after retraining a substantial increase in thresholds for up to 3 years when tested with long bars. There was no recovery of discrimination when the animals were tested with short bars. Lesions which involved area 17 plus small parts of 18, or lesions of areas 18 and 19, produced no retention deficit and resulted in an increase in thresholds only at low contrast and narrow width. These experiments revealed an excellent correlation between lesion locus and size and behavioral deficit. They indicate that the cortical representation of bar orientation used for discrimination is distributed within and across areas 17 and 18. The spread of the distribution depends on other stimulus parameters such as bar width and length. Furthermore the experiments show that neither the most narrowly tuned cells nor the X-cell system is required for fine orientation discrimination of a long bar.

Animals↗
PubMed1990

Staircase procedure and constant stimuli method in cat psychophysics.

We measured 73.5% correct just noticeable differences (JNDs) in bar orientation with the method of constant stimuli and with a Wetherill and Levitt staircase procedure, using a total of 25 cats. For the same number of trials per threshold assessment, the variability of the threshold remained independent of the testing method used. However, the JNDs measured using the method of constant stimuli were significantly influenced by the range of the orientation differences (ODs) utilized for measuring the JND. This effect was particularly large in incompletely trained cats, but it also was significant in extensively trained subjects. On the other hand, staircase threshold measurements were not affected by the starting OD, independently of how well the animals had been trained. This shows that the staircase procedure is a more efficient instrument with which to measure JNDs in orientation than is the method of constant stimuli. With the staircase procedure, we found that the JNDs measured at oblique reference orientations did not exceed those measured at principal reference orientations (no oblique effect). Two earlier studies from this laboratory using the method of constant stimuli did report an oblique effect. Our data suggest that this oblique effect might stem from a less efficient training at the right oblique reference orientation in these studies, combined with a relatively inefficient testing procedure such as the constant stimuli method.

Animals↗
PubMed1990

Illusory contour orientation discrimination in the cat.

We present the first evidence that a non-human species (the cat) is able to discriminate the orientation of illusory contours. Following Vogels and Orban45, we used two types of illusory contours. In one type, the illusory contour was defined by a number of contour-inducing semicircles, of which the endpoints were separated by a gap. In the other pattern, the inducing semicircles were shifted in phase along their diameter and their endpoints were aligned along the contour. Just noticeable differences in orientation were measured (at the 73.5% correct level), using a Wetherill and Levitt49 staircase procedure. Values in the order of 11 degrees were obtained when using the first type of illusory contour. Just noticeable differences with the second type were in the order of 17 degrees. Reducing the salience of the illusory contour, whether by scrambling the contour, or by decreasing the number or the contrast of inducing semicircles, systematically increased discrimination thresholds.

Animals↗
PubMed1990

Influence of retinal lesions on grating acuity of the cat.

Grating acuity was investigated behaviorally in the cat. Retinal lesions of increasing diameter centered on the area centralis were made by photocoagulations in one eye, while the intact eye was used as control. Lesion size evaluated from fundus photographs was precisely correlated with the anatomical lesion size measured in retinal whole mounts. Grating acuity improved with increasing grating area in cats with intact retinae and after small (less than 3 degrees diameter) retinal lesions but not after large lesions (greater than 4 degrees diameter). Overall, grating acuity clearly decreased when lesions became larger than 4 degrees in diameter. The acuity-eccentricity relationship closely fits the cutoff frequency of brisk sustained cells at the corresponding eccentricities.

Animals↗
PubMed1990

Speeding up visual discrimination learning in cats by differential exposure of positive and negative stimuli.

We have developed an adaptive training method which considerably reduces the total time required to train cats to threshold in an orientation discrimination task. During training, the animals are given greater exposure in time to the positive stimulus compared to the negative one. Therefore, this method has been coined the differential exposure method (DEM). The greater exposure to the positive stimulus reduces the number of errors an animal commits during training and thereby enhances speed of learning. Indeed, with the DEM, 34 daily sessions sufficed to train cats to threshold for 2 different reference orientations. Furthermore, the DEM was effective not only for simple stimuli such as real bars but also for complex stimuli such as illusory contours. Finally, the DEM was equally effective for training naive cats which had undergone large visual cortical lesions as it was for normal animals.

Animals↗
PubMed1990

Bar orientation discrimination in the cat.

We have measured orientation-discrimination thresholds of 4 deg in the cat, confirming an earlier study of Vandenbussche and Orban (1983). Unlike Vandenbussche and Orban (1983), we found that orientation-discrimination performance is not better at principal, as compared to oblique, reference orientations (no oblique effect). Despite the absence of the oblique effect, and despite the discrimination thresholds which were elevated by a factor of 4 compared to humans, orientation-discrimination performance of cats and humans is qualitatively similar in a number of aspects. First, orientation-discrimination performance as a function of length and contrast is qualitatively similar to human performance. Second, as in humans, detection and discrimination of the stimuli are closely related. Finally, randomizing the contrast between the stimuli does not affect orientation-discrimination performance. This suggests that similar computations underlay orientation-discrimination performance in both species. In summary, our results confirm that the cat is a useful model for human orientation-discrimination performance.

Animals↗
PubMed1990

Orientation discrimination in the cat: a distributed function.

Cats were trained to make fine orientation discriminations with stimuli similar to those used in physiological experiments--narrow, light bars 12 degrees long--before and after various combinations of lesions of areas 17 and 18. Discrimination thresholds were measured at different contrast levels and different bar widths, both pre- and postoperatively, for up to 1.5 years after the lesion. For high contrast stimuli, lesions restricted to area 17 or area 18 had little effect, but those lesions involving area 17 and a substantial part of area 18 raised thresholds. In the latter case there was a relationship between the amount of area 18 spared and the bar width at which discrimination was impaired. At low contrast deficits were seen only for narrow widths. These results lead to the following conclusions. (i) Orientation discrimination is a function distributed within and across areas 17 and 18. (ii) How this function is distributed in this cortex depends on stimulus width. (iii) The X system does not carry the signal necessary for orientation discrimination. (iv) Cells most narrowly tuned for orientation, which reside in the part of area 17 subserving central vision, do not determine the orientation discrimination threshold.

Animals↗
PubMed1988

Stimulus contrast and visual cortical lesions.

Intact animals can make fine orientation discriminations over a wide range of contrasts. After ablation of area 17 deficits in orientation discrimination are observed only at low contrast. The relevance of this finding for the design of sensitive ablation experiments is discussed.

Animals↗
PubMed1986

Velocity discrimination in the cat.

After considerable training (over 2 years) we measured the just noticeable differences (JNDs) in velocity as a function of reference velocity in three cats. The velocity discrimination curve plotting JNDs in velocity, expressed as Weber fractions as a function of reference velocity is U-shaped with optimal performance at reference speeds between 25 and 60 degrees/sec. The discrimination curve changed little with a tenfold change in slit width. Compared to the human velocity discrimination curve determined with the same test apparatus, the feline curve is narrower and shifted towards faster velocities and larger Weber fractions. These results support our specific linking hypothesis between velocity tuned cells as observed in cortical areas 17 and 18 of the cat, and velocity discrimination.

Animals↗
PubMed1986

Human orientation discrimination: changes with eccentricity in normal and amblyopic vision.

The authors measured orientation discrimination of a single line as a function of eccentricity, line length, and standard orientation. Orientation discrimination improved with increasing line length at all eccentricities. The shortest length at which orientation discrimination was optimal increased with eccentricity. When a line length was used for which discrimination was optimal at all eccentricities, it was found that orientation discrimination performance changed little with increasing eccentricity. Under the same conditions, the oblique effect in orientation discrimination decreased with increasing eccentricity. Similar results were also obtained in both eyes of strabismic amblyopes. The difference between the just noticeable differences in orientation of the amblyopic and nonamblyopic eye decreased with increasing line length for central vision. This interocular difference also decreased with increasing eccentricity. The absence of the oblique effect in orientation discrimination at large eccentricities support the hypothesis that the area 17 S-cell orientation anisotropy underlies the oblique effect in orientation discrimination of long lines since this sensorial anisotropy is limited to the central visual field.

Adult↗
PubMed1979

Leakage of fluorescein: first sign of juvenile diabetic retinopathy. Role of diabetic control and of duration of diabetes.

In order to ascertain the first vascular lesions responsible for juvenile diabetic retinopathy, 408 fluorescein angiographies were performed in 114 diabetic children and adolescents whose diabetes became clinically apparent before the age of 14 years. Compared with regular ophthalmoscopy, fluorescein angiography doubles the frequency of the diagnosis of incipient retinopathy. In addition to the classical diabetic lesions, fluorescein leakages are demonstrated in 50% of diabetic eyes with initial retinopathy. They probably reflect early changes in capillary permeability. They appear often before microaneurysms. Duration of diabetes as well as insufficient and poor metabolic control considerably increase the frequency of retinopathy.

Adolescent↗