Biomedical subjects

J N van der Geest

Publications and source records attributed to J N van der Geest.

14 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

The cervico-ocular reflex is increased in whiplash injury patients.

Whiplash-associated disorders (WAD) are a major problem in the Western world, which put a formidable financial burden on modern society and which evoke an emerging debate on the true nature of their origin. To date there is no generally accepted test that allows us to diagnose WAD objectively. Because whiplash injury causes dysfunction of proprioception in the neck, we investigated the characteristics of the cervico-ocular reflex (COR) of presumptive WAD patients. These patients and age-matched healthy controls were rotated at different stimulus peak velocities in the dark while their head was fixed in space. The gain values of the COR were significantly increased in the patient population at a wide range of stimulus peak velocities with maximum difference at the lower frequencies (p = 0.037, ANOVA). Hence, although larger numbers of patients should be measured, the COR gain appears to be a parameter that may permit an objective diagnosis of WAD.

Adult↗

PubMed2004

In search of neurophysiological markers of pervasive developmental disorders: smooth pursuit eye movements?

Genetic studies of autism would benefit from the identification of (neurophysiological) markers of the disease. Reports that subjects with autism suffer from abnormalities of visual motor processing, indicate that abnormalities in smooth pursuit eye movements (SPEM) may be a marker of the disorder. Sixteen high-functioning school-aged children with pervasive developmental disorder (PDD) were compared with a matched group of eighteen normally developing controls on performance of a SPEM task and a task which tested the integrity of visually guided saccadic eye movements. Both groups of children had normal eye movements during performance of these tasks. Thus abnormalities in SPEM would appear not to be a marker of PDD. The earlier reported abnormalities in visual motion processing might need to be reinterpreted.

Child↗

PubMed2004

Short-term adaptation of the cervico-ocular reflex.

The cervico-ocular reflex (COR) works in conjunction with the vestibulo-ocular reflex (VOR) and the optokinetic reflex (OKR) in order to prevent visual slip over the retina during head movement. The COR induces eye movements in response to proprioceptive signals from the neck. We investigated whether the COR gain can be adapted by inducing a mismatch between vision and neck proprioception, in analogy to VOR adaptation. Thirteen healthy subjects were rotated in the dark in a trunk-to-head manner (the head fixed in space while the body passively rotated sinusoidally with a peak velocity of 1.25 degrees /s). Eye movements were recorded with infrared video-oculography under various adaptive conditions. Analysis showed a small but significant reduction in COR gain in the suppression conditions. This means that the cervico-ocular reflex can be modified after only 10 min of concurrent visual and cervical stimulation.

Adaptation, Physiological↗

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↗

PubMed2003

Compensatory increase of the cervico-ocular reflex with age in healthy humans.

The cervico-ocular reflex (COR) is an ocular stabilization reflex that is elicited by rotation of the neck. It works in conjunction with the vestibulo-ocular reflex (VOR) and the optokinetic reflex (OKR) in order to prevent visual slip over the retina due to self-motion. The gains of the VOR and OKR are known to decrease with age. We have investigated whether the COR, a reflexive eye movement elicited by rotation of the neck, shows a compensatory increase and whether a synergy exists between the COR and the other ocular stabilization reflexes. In the present study 35 healthy subjects of varying age (20-86 years) were rotated in the dark in a trunk-to-head manner (the head fixed in spaced with the body passively rotated under it) at peak velocities between 2.1 and 12.6 deg s-1 as a COR stimulus. Another 15 were subjected to COR, VOR and OKR stimuli at frequencies between 0.04 and 0.1 Hz. Three subjects participated in both tests. The position of the eyes was recorded with an infrared recording technique. We found that the COR-gain increases with increasing age and that there is a significant covariation between the gains of the VOR and COR, meaning that when VOR increases, COR decreases and vice versa. A nearly constant phase lag between the COR and the VOR of about 25 deg existed at all stimulus frequencies.

Adult↗

PubMed2002

Inhibition of saccade initiation by preceding smooth pursuit.

In this study, we investigated the influence of smooth-pursuit eye movements on saccade initiation in response to a sudden jump of a continuously moving target. We replicated the finding by Tanaka et al. (1998) that saccadic eye movements in the direction opposite to preceding pursuit have longer latencies than those in the same direction. We confirmed that this asymmetry is indeed due to an inhibitory effect of smooth pursuit on saccade initiation in the opposite direction rather than facilitation of saccade initiation in the same direction. The inhibitory effect decreased strongly when subjects knew the jump direction in advance. This supports the notion that the prolonged latencies of backward saccades are not due to orbital mechanics or low-level motor processing. Furthermore, we found that the range of saccade directions inhibited by a pursuit movement is broad, covering all directions that did not have the same horizontal component as the pursuit direction. This is in contrast with the predictions of "Inhibition of Saccade Return" (ISR, Hooge and Frens 2000), which is restricted to a smaller confined area.

Distance Perception↗

PubMed2002

Recording eye movements with video-oculography and scleral search coils: a direct comparison of two methods.

A video-based 2D eye-tracking system (EyeLink version 2.04, SR Research Ltd/SMI) was compared with the scleral search coil technique for its performance on recording the properties of fixations and saccadic eye movements. Fixation positions and saccadic properties (amplitude, duration, and peak velocity) were calculated independently from the data of the two systems that recorded eye positions simultaneously. Fixation positions were well correlated between the video and the coil output with an average discrepancy of <1 degree over a tested range of 40 by 40 degree of visual angle. With respect to the saccade analysis, the values measured by the video system were fitted as a linear function of the values measured by the coil system. Highly correlated linear fits with slopes near one were obtained for all the saccadic parameters. Main sequence relationships (amplitudes-duration and amplitude-peak velocity) were also similar for both systems. A disadvantage of the video method is its low sample rate of 250 Hz. The relatively noisier estimate of all parameters of small saccades could be attributed to this low sampling frequency.

Eye Movements↗

PubMed2002

Looking at images with human figures: comparison between autistic and normal children.

Based on clinical observations of abnormal gaze behavior of autistic children, it has been suggested that autistic children have a problem in processing social information. Several studies on eye movements have indeed found indications that children with autism show particularly abnormal gaze behavior in relation to social stimuli. However, the methodology used in such investigations did not allow for precise gaze analysis. In the present study, the looking behavior of autistic children toward cartoon-like scenes that included a human figure was measured quantitatively using an infrared eye-tracking device. Fixation behavior of autistic children was similar to that of their age- and IQ-matched normal peers. These results do not support the notion that autistic children have a specific problem in processing socially loaded visual stimuli. Also, there is no indication for an abnormality in gaze behavior in relation to neutral objects. It is suggested that the often-reported abnormal use of gaze in everyday life is not related to the nature of the visual stimuli but that other factors, like social interaction, may play a decisive role.

Autistic Disorder↗

PubMed2002

Gaze behavior of children with pervasive developmental disorder toward human faces: a fixation time study.

BACKGROUND: The abnormal gaze behavior of autistic children toward human faces, as observed in daily-life situations, are investigated in two fixation time studies. It has been argued that faces are a special kind of stimuli for normal individuals and that this might not be the case for autistic children. METHODS: A group of high-functioning autistic children (including a group of sub-threshold PDD-NOS children) was compared with a group of normal children, with respect to their fixation behavior for photographs of human faces. Using an infrared eye-tracking device, fixation times for the whole face and for the facial elements of faces were compared between the two groups. The first study dealt with faces having an emotional expression. The second study dealt with neutral faces presented either upright or upside-down. RESULTS: Results of the two studies showed that autistic children have the same fixation behavior as normal children for upright faces, with or without an emotional expression. Furthermore, results of the second study showed that normal children spent less time looking at upside-down faces, but that the fixation times of autistic children were not influenced by the orientation of the faces. CONCLUSIONS: These results plead against the notion that the abnormal gaze behavior in everyday life is due to the presence of facial stimuli per se. Furthermore, the absence of a face orientation effect in autistic children might be a reflection of a lack of holistic processing of human faces in autism.

Attention↗

PubMed2002

Scleral search coils influence saccade dynamics.

The scleral search coil technique is commonly used for recording eye movements. The goal of this paper is to investigate to what extent the placement of scleral search coils onto the eyes influences the kinematics of saccades. To that end saccadic eye movements of human subjects were recorded with an infrared video system, while they wore coils and we compared the main sequence properties with recordings in which no coils were mounted on the eyes. It was found that saccades last longer (by about 8%) and become slower (by about 5%) when both eyes wear coils. This is truly due to the fact that the coils are on the eyes and not due to other factors that are part of this method, such as the scleral anesthesia. The influence of coils in both eyes was also observed when one coil was mounted on one eye only. Therefore the effect that the coils have on the eye movements cannot be attributed to purely mechanical factors, such as inertial load on the eyeball or increased friction. Rather the coils appear to change the oculomotor command signals that drive the saccadic eye movements.

Biotechnology↗

PubMed2001

Eye movements, visual attention, and autism: a saccadic reaction time study using the gap and overlap paradigm.

BACKGROUND: On the basis of the literature on autism, it was hypothesized that children with autism have deficits in attentional (dis-)engagement mechanisms. METHODS: A saccadic gap-overlap task was used to study visual engagement and disengagement in 16 high-functioning autistic children of about 10 years of age and 15 age- and IQ-matched normal control children. Subjects were asked to make saccadic eye movements from a fixation point to a suddenly appearing target as fast as possible. The saccadic reaction time was compared in two conditions: 1) the overlap condition, in which the fixation point was continuously visible, and 2) the gap condition, in which the fixation point was turned off 200 msec before the target appeared. RESULTS: Although no differences between the groups in either condition was observed, the gap effect (i.e., the difference in saccadic reaction time between the overlap condition and the gap condition) was smaller in the autistic group than in the control group. CONCLUSIONS: We concluded that autistic children show a lower level of attentional engagement.

Attention↗

PubMed1999

Sources of position-perception error for small isolated targets.

It has often been reported that, in the presence of static reference stimuli, briefly presented visual targets are perceived as being closer to the fixation point than they actually are. The first purpose of the present study was to investigate whether the same phenomenon can be demonstrated in a situation without static reference stimuli. Experiment 1, with position naming as the task, showed that such a central shift is also observed under these conditions. This finding is of importance because it completes an explanation for central near-location errors in the partial-report bar-probe task. The second purpose of the present study was to provide an explanation for these central shifts. For this explanation information about the exact size of the central shift is required. In Exps. 2, 3, and 4, with cursor setting as the task, it was attempted to assess more precisely the size of the central shifts. These experiments revealed that two different factors determine the results in cursor setting tasks; a factor "target position" and a factor "cursor position." Experiment 5 showed that it is the point of fixation, not the fixation point, that serves, at least in part, as the reference point in this type of task. All the findings together allow us to conclude that the target positions are underestimated by about 10%. From vision research it is known that saccadic eye movements, performed for bringing a target in the fovea, also show an undershoot of about 10%. It is therefore concluded that the system in charge of saccadic eye movements also provides the metric in visual space within a single eye fixation.

Fixation, Ocular↗

PubMed1996

Attending to color with proper fixation.

In contemporary theorizing, there is a controversy about the role of spatial location in the selection of visual information; some theories postulate that position plays a unique role, whereas other theories hold that position is just one selection dimension that is not different from other dimensions, such as color and shape. In this context, a paradigm introduced by Tsal and Lavie (1988) promised to be of fundamental importance. With that paradigm, Tsal and Lavie found that, after reporting a first letter of a prespecified color, subjects preferred to switch their reporting to letters from array positions adjacent to that letter over continuing to report letters of the same color as that of the first letter. This switch from color to position provided firm evidence in favor of the "position-special" views as opposed to the "all-attributes-are-equal" views. In the present study, six experiments, employing Tsal and Lavie's paradigm and variations of that paradigm, are reported. Experiments 1,2,4, and 5 show that evidence for a switch from selection on the basis of color to selection on the basis of position is not obtained when subjects are forced to fixate the fixation point and possibly also not under normal contrast conditions without fixation controls. Experiment 3 shows that switching from color to position is difficult. Experiments 2, 5, and 6 show that evidence for a switch is obtained only under low-contrast conditions when subjects are not forced to fixate the fixation point. It is concluded that the Tsal and Lavie paradigm is an asymmetric paradigm. The results reported by Tsal and Lavie constituted a major threat for the "all-attributes-are-equal" theories and provided firm support for the "position-special" theories. The results reported in the present study are compatible with the all-attributes-are-equal theories, but, at the same time, do not constitute a major threat for the contemporary position-special theories.

Adult↗