Steen, J. van der

Factors related to impaired visual orienting behavior in children with intellectual disabilities (Article)

2012-05-07T00:00:00Z

It is generally assumed that children with intellectual disabilities (ID) have an increased risk of impaired visual information processing due to brain damage or brain development disorder. So far little evidence has been presented to support this assumption. Abnormal visual orienting behavior is a sensitive tool to evaluate impaired visual information processing. Therefore, the main objective of this study was to investigate possible correlations between the children's characteristics (age, gender, level of ID, mobility, gestational age, cerebral palsy, Down syndrome, visual acuity, strabismus, nystagmus, and epilepsy), and abnormal visual orienting behavior. We quantified data on visual orienting behavior, in terms of visual processing time and ocular motor fixations, in 88 children with ID aged 4-14 years. These visual parameters were combined with data collected from the children's medical records (predictors) and were put in a Pearson bivariate correlation analysis. A predictor was included for multiple regression analysis if the Pearson's correlation coefficient had a level of significance of p<0.05. As shown by multiple regression analysis, age, level of ID, and Down syndrome significantly affected visual processing time. Mobility, strabismus, and nystagmus significantly affected fixation quality.Using a systematic approach, we confirmed the hypothesis that children with ID have an increased risk of impaired visual information processing which is related to a low IQ.

Quantification of visual orienting responses to coherent form and motion in typically developing children aged 0-12 years (Article)

2012-05-01T00:00:00Z

PURPOSE. Brain damage or brain development disorders can affect (the maturation of) visual processing functions, such as form and motion detection. The aim of our study was to investigate visual orienting responses of children to a coherent form and motion stimulus as a measure for maturation of visual information processing. METHODS. The 213 typically developing children aged 0-12 years included in this study were shown a 100% coherent form and motion expansion stimulus on a remote eye tracking monitor. Orienting eye movements were quantified in terms of ocular motor reaction time to fixation (RTF). Children were divided in age groups, and their performance was compared to 30 healthy adults with a mean age of 24.49 years (SD 3.62 years). RESULTS. The RTF values of coherent form in children up to six years old were significantly higher compared to the adult group (P < 0.05, Dunnett post-hoc test). For motion, mature levels were reached at eight years old. RTF values depended on stimulus type (F1,168= 240.8, P < 0.001) and age (F11,168= 25.8, P < 0.001), and there was a significant age by stimulus type interaction (F11,168 = 2.2, P < 0.05). CONCLUSIONS. Remote eye tracking may provide objective insight into the maturation of visual information processing of coherent form and motion without complex instructions or active cooperation. The quantification of typical visual orienting behavior in childhood may be used as a reference for children with brain dysfunction.

Cerebral Visual Impairment: Which perceptive visual dysfunctions can be expected in children with brain damage? A systematic review (Article)

2010-11-01T00:00:00Z

The current definition of Cerebral Visual Impairment (CVI) includes all visual dysfunctions caused by damage to, or malfunctioning of, the retrochiasmatic visual pathways in the absence of damage to the anterior visual pathways or any major ocular disease. CVI is diagnosed by exclusion and the existence of many different causes and symptoms make it an overall non-categorized group. To date, no discrimination is made within CVI based on types of perceptive visual dysfunctions. The aim of this review was to outline which perceptive visual dysfunctions are to be expected based on a number of etiologies of brain damage and brain development disorders with their onset in the pre-, peri- or postnatal period. For each period two etiologies were chosen as the main characteristic brain damage. For each etiology a main search was performed. The selection of the articles was based on the following criteria: age, etiology, imaging, central pathology and perceptive visual function test. The perceptive visual functions included for this review were object recognition, face recognition, visual memory, orientation, visual spatial perception, motion perception and simultaneous perception. Our search resulted in 11 key articles. A diversity of research history is performed for the selected etiologies and their relation to perceptive visual dysfunctions. Periventricular Leukomalacia (PVL) was most studied, whereas the main tested perceptive visual function was visual spatial perception. As a conclusion, the present status of research in the field of CVI does not allow to correlate between etiology, location and perceptive visual dysfunctions in children with brain damage or a brain development disorder. A limiting factor could be the small number of objective tests performed in children experiencing problems in visual processing. Based on recent insights in central visual information processing, we recommend an alternative approach for the definition of CVI that is based on functional visual processing, rather than anatomical landmarks. This could be of benefit in daily practice to diagnose CVI.

Peaks and Troughs of Three-Dimensional Vestibulo-ocular Reflex in Humans (Article)

2010-09-01T00:00:00Z

The three-dimensional vestibulo-ocular reflex (3D VOR) ideally generates compensatory ocular rotations not only with a magnitude equal and opposite to the head rotation but also about an axis that is collinear with the head rotation axis. Vestibulo-ocular responses only partially fulfill this ideal behavior. Because animal studies have shown that vestibular stimulation about particular axes may lead to suboptimal compensatory responses, we investigated in healthy subjects the peaks and troughs in 3D VOR stabilization in terms of gain and alignment of the 3D vestibulo-ocular response. Six healthy upright sitting subjects underwent whole body small amplitude sinusoidal and constant acceleration transients delivered by a six-degree-of-freedom motion platform. Subjects were oscillated about the vertical axis and about axes in the horizontal plane varying between roll and pitch at increments of 22.5° in azimuth. Transients were delivered in yaw, roll, and pitch and in the vertical canal planes. Eye movements were recorded in with 3D search coils. Eye coil signals were converted to rotation vectors, from which we calculated gain and misalignment. During horizontal axis stimulation, systematic deviations were found. In the light, misalignment of the 3D VOR had a maximum misalignment at about 45°. These deviations in misalignment can be explained by vector summation of the eye rotation components with a low gain for torsion and high gain for vertical. In the dark and in response to transients, gain of all components had lower values. Misalignment in darkness and for transients had different peaks and troughs than in the light: its minimum was during pitch axis stimulation and its maximum during roll axis stimulation. We show that the relatively large misalignment for roll in darkness is due to a horizontal eye movement component that is only present in darkness. In combination with the relatively low torsion gain, this horizontal component has a relative large effect on the alignment of the eye rotation axis with respect to the head rotation axis.

Assessment of visual orienting behaviour in young children using remote eye tracking: Methodology and reliability (Article)

2010-06-01T00:00:00Z

Human orienting behaviour requires a complex interaction between the visual and the oculomotor system. We present orienting gaze data measured in children using a remote eye tracking system. The aim of the study was to validate a data analysis method which did not require off-line correction of data gaps due to eye blinking or inadequate gaze tracking. In two sessions, blocks of short movies, amongst others cartoons, were shown to 35 children (2-9 years) for a test-retest analysis. The cartoons were subsequently shown in one of the monitor corners. Orienting eye movements were analysed on the basis of saccadic reaction time (SRT), reaction time to fixation (RTF) of cartoon and gaze fixation area (GFA) Differences were tested for significance using the Wilcoxon-signed ranks test and reliability was assessed using the intraclass correlation coefficient (ICC). SRT values could be calculated in ∼50% of gaze data and ranged between 150(30)ms (mean(SD)) and 390(190)ms (average SRTminand SRTmaxvalues of all subjects). RTF values could be derived in ∼90% of gaze data with an average RTFminof 210(30)ms and RTFmaxof 570(160)ms. Test-retest analysis showed a significant increase of GFA during the second session with ∼5% (P<0.05). The reliability of RTFminand GFA was best with an ICC of 0.84 and 0.80, respectively (P<0.0001). We conclude that remote eye tracking is well suited for quantification of timing and executing oculomotor fixations during orienting behaviour tasks. The presented method may be applied in young children with developmental disorders or brain damage.

Platform accelerations of three different whole-body vibration devices and the transmission of vertical vibrations to the lower limbs (Article)

2009-10-01T00:00:00Z

Physical whole-body vibration (WBV) exercises become available at various levels of intensity. In a first series of measurements, we investigated 3-dimensional platform accelerations of three different WBV devices without and with three volunteers of different weight (62, 81 and 100 kg) in squat position (150° knee flexion). The devices tested were two professional devices, the PowerPlate and the Galileo-Fitness, and one home-use device, the PowerMaxx. In a second series of measurements, the transmission of vertical platform accelerations of each device to the lower limbs was tested in eight healthy volunteers in squat position (100° knee flexion). The first series showed that the platforms of two professional devices vibrated in an almost perfect vertical sine wave at frequencies between 25-50 and 5-40 Hz, respectively. The platform accelerations were slightly influenced by body weight. The PowerMaxx platform mainly vibrated in the horizontal plane at frequencies between 22 and 32 Hz, with minimal accelerations in the vertical direction. The weight of the volunteers reduced the platform accelerations in the horizontal plane but amplified those in the vertical direction about eight times. The vertical accelerations were highest in the Galileo (∼15 units of g) and the PowerPlate (∼8 units of g) and lowest in the PowerMaxx (∼2 units of g). The second series showed that the transmission of vertical accelerations at a common preset vibration frequency of 25 Hz were largest in the ankle and that transmission of acceleration reduced ∼10 times at the knee and hip. We conclude that large variation in 3-dimensional accelerations exist in commercially available devices. The results suggest that these differences in mechanical behaviour induce variations in transmissibility of vertical vibrations to the (lower) body.

Oogbewegingen in drie dimensies bij het konijn onder passieve en actieve omstandigheden (Doctoral Thesis)

1981-09-09T00:00:00Z

De reflexen stabilisatie van die de verantwoordelijk zijn ogen in de ruimte voor: de zijn sedert tientallen jaren uitvoerig onderzocht. Doordat. het konijn in gefixeerde toestand zelden spontane oogbewegingen maakt is dit dier veelvuldig gebruikt voor de bestudering van de optokinetische (OKR) en vestibule-oculaire reflex (VOR). Het meeste onde:r:z.oek heeft zich gericht op de oogbewegingen in het horizontale vlak. Er is weinig bekend over de stabilisatie van de ogen in het verticale en torsie vlak. In dit proefschrift worden de eigenschappen van de VOR bij het konijn in het donker en het licht beschreven in horizontale, verticale en torsie richting. De konijnen werden sinusaidaal geschommeld met een amplitude van 20 graden piek tot piek en frekwenties varierend van 0.008 tot 2 Hz. Bij de registratie van oog- en kopbewegingen is gebruik gemaakt van verticale en horizontale inductiespoelen in een roterend magnetisch veld. De twee oogspoelen waren permanent op het oog geimplanteerd. De stabilisatie van het oog in de ruimte bleek verschillend in het horizontale, verticale en torsie vlak. In het lage frekwentiegebied nam de gain van de VOR in het horizontale vlak sterk af terwijl de fasevoorsprong toenam. Bij schommelingen in het verticale en torsievlak werd in het lage frekwentiegebied een belangrijke bijdrage van de otolieten gevonden. De compensatie is aanzienlijk minder bij de schommelingen om de torsie sagittale as dan bij schommelingen om de sagitale as.. Voor alle drie de vlakken was de compensatie in het licht over het gehele frekwentiegebied min of meer constant. De gains van de compensatoire oogbewegingen in het horizontale, verticale en torsie vlak varieerden respectievelijk van 0.82-0.70, 0.92-0.83 en 0.59-0.65. Ook bij schommelingen om intermediaire assen in het donker bleek in het lage frekwentiegebied een afwezigheid van de compensatie in het horizontale vlak