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Biomedical subjects

G C Lagers-van Haselen

Publications and source records attributed to G C Lagers-van Haselen.

11 recordsLinked to original sources
PubMed2006

Visual search deficits in Williams-Beuren syndrome.

Williams-Beuren syndrome (WBS) is a rare genetic condition characterized by several physical and mental traits, such as a poor visuo-spatial processing and a relative strength in language. In this study we investigated how WBS subjects search and scan their visual environment. We presented 10 search displays on a computer screen to WBS subjects as well as control subjects, with the instruction to find a target out of several stimulus elements. We analyzed the eye movement patterns for fixation characteristics and systematicy of search. Fixations generally lasted longer in WBS subjects than in control subjects. WBS subjects made more fixations at a stimulus element they had already looked at and more fixations that were not aimed at a stimulus element at all, decreasing the efficiency of search. These outcomes lead to the conclusion that visual search of individuals with Williams-Beuren syndrome is less effective than in control subjects. This finding may be related to their motor deficits, an impaired processing of global visual information and/or deficits in working memory and could reflect impairments within the dorsal stream.

Adolescent↗
PubMed2005

Visual depth processing in Williams-Beuren syndrome.

Patients with Williams-Beuren Syndrome (WBS, also known as Williams Syndrome) show many problems in motor activities requiring visuo-motor integration, such as walking stairs. We tested to what extent these problems might be related to a deficit in the perception of visual depth or to problems in using this information in guiding movements. Monocular and binocular visual depth perception was tested in 33 patients with WBS. Furthermore, hand movements to a target were recorded in conditions with and without visual feedback of the position of the hand. The WBS group was compared to a group of control subjects. The WBS patients were able to perceive monocular depth cues that require global processing, but about 49% failed to show stereopsis. On average, patients with WBS moved their hand too far when no visual feedback on hand position was given. This was not so when they could see their hand. Patients with WBS are able to derive depth from complex spatial relationships between objects. However, they seem to be impaired in using depth information for guiding their movements when deprived of visual feedback. We conclude that the problems that WBS patients have with tasks such as descending stairs are not due to an inability to judge distance.

Adolescent↗
PubMed2004

Saccade dysmetria in Williams-Beuren syndrome.

Numerous studies have described the poor visuo-spatial processing capacities of subjects with Williams-Beuren syndrome (WBS), a genetically based developmental disorder. Since visual perception and eye movements are closely related we hypothesized that the poor visuo-spatial processing capacities of subjects with WBS might be related to a poor saccadic control. Thereto, we recorded horizontal and vertical saccadic eye movements to targets using infrared video-oculography in 27 subjects with WBS and eight healthy controls. In the WBS group saccadic gains were highly variable, both between and within individual subjects, and they often needed more than one correction saccade to reach the target. Ten (out of a subgroup of 22) WBS subjects showed a large number of hypometric and/or hypermetric saccades, and, also a left-right asymmetry in saccadic gains was observed in WBS. We conclude that the observed impairments in saccadic control are likely to affect the proper processing of visuo-spatial information.

Adolescent↗
PubMed2000

Copying strategies for patterns by children and adults.

In the present study, eve movements during the copying of a pattern were analyzed to compare visual strategies of adults and children. Subjects had to build an accurate copy of spatial block patterns. Tested variables were the incidence and the duration of ocular dwelling in the pattern area (where the pattern to be copied was located), the work area (where the copy was made), and the source area (where the blocks were that could be used for creating the copy). Furthermore, to unravel employed strategies, sequences of dwelled areas were investigated. Previous studies reported that adults employ repetitive visual scanning strategies to accomplish the task instead of strategies depending upon an internal representation. The present results show that the II children, within the ages of 7 to 12 years, made more eye movements and fixations of longer duration during copy tasks than the 11 adults. The visual strategies of the children were highly comparable to those of adults. Memory was restricted to one block, while color and location seemed to be remembered together.

Adult↗
PubMed1994

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.

Forearm↗
PubMed1990

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.

Animals↗
PubMed1988

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.

Animals↗
PubMed1987

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.

Animals↗
PubMedDate not supplied

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.

Animals↗