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Biomedical subjects

P Cornelissen

Publications and source records attributed to P Cornelissen.

14 recordsLinked to original sources
PubMed1995

Contrast sensitivity and coherent motion detection measured at photopic luminance levels in dyslexics and controls.

Development dyslexics perform differently from controls on a number of low level visual tasks. We carried out three experiments to explore some of these differences. Dyslexics have been found to have reduced luminance contrast sensitivity at mesopic luminance levels. We failed to replicate this finding at photopic luminance levels. We also compared the (photopic) coherent motion detection thresholds of groups of child and adult dyslexics with those of age matched controls. Dyslexics were significantly less sensitive to motion. The results are discussed in relation to a recent suggestion that developmental dyslexia may be associated with a magnocellular visual deficit.

Adolescent↗
PubMed1994

What children see affects how they spell.

The authors predicted that children who have experienced frequent visual confusion of text during their development because of unstable binocular control may be prevented from discovering the rules and patterns of English orthography. The authors compared the spelling errors made by children who had unstable binocular vision with those of children who had stable binocular vision and the same spelling ability. The subjects were drawn from a clinical population of children referred because of suspected reading difficulties; though they were of mixed abilities, they were generally poor spellers and readers. Children with unstable binocular control made spelling errors which were more phonologically plausible than those made by the control group with normal binocular vision.

Child↗
PubMed1993

The stability of binocular fixation during reading in adults and children.

The authors recorded the binocular eye-movements of children and adults while they read single words appropriate for their reading ability. Normal data were obtained from nine- to 11-year-old primary-school children and adults, because very little is known about changes in binocular vergence during reading. These normal data were compared with those from poor readers of the same age who had passed or failed the Dunlop Test. On average, normal children made larger vergence errors while they fixated words than did adults. There were no differences between the groups of children, therefore the authors conclude that poor vergence control during reading fixations is not the immediate cause of the non-word error effect found among children who fail the Dunlop Test.

Adult↗
PubMed1992

Covering one eye affects how some children read.

The Dunlop Test was used to identify unstable binocular control in a group of 32 mixed-ability children. They were compared with 32 reading age-matched controls. The children were then asked to read two lists of single real words of equal linguistic difficulty: one with both eyes open and the other with the left eye occluded. Only children who failed the Dunlop Test made fewer non-word errors when they read with one eye. This result provides additional support for the theory that unstable binocular control can directly affect how children read. In addition, these findings suggest that this effect must be due, at least in part, to some interaction between the images from the two eyes.

Child↗
PubMed1991

What children see affects how they read.

Children of mixed abilities were given three single-word lists to read, matched for linguistic complexity. The visual component of the task was made harder by reducing the print size with each new list. The reading errors made by children who did and who did not have a visual impairment were compared. The visually impaired children's pattern of reading errors changed as their vision was stressed by the reduction in print size; their errors became non-words (neologisms). This finding suggests a link between the efficiency of visual processing and the accuracy of reading of these children.

Aptitude↗
PubMed1987

Assessment of tibial stiffness by vibration testing in situ--III. Sensitivity of different modes and interpretation of vibration measurements.

Post mortem vibration measurements on one human tibia during gradual transection reveal the vibration modes and frequencies of a tibia during a simulated healing. The modes are identified in a tibia in an above knee amputation specimen with the leg in two positions: hanging down with the knee flexed (90 degrees) and supported in a special designed bone clamping splint (knee flexed 45 degrees). The vibration measurements are analysed using Modal Analysis and are translated to mechanical stiffness by mathematical modelling. The single bending 'free-free' mode turned out to be more sensitive to weakening of one cross-section than the 'rigid body' and single bending 'hinged-spring' modes. The error on the assessed value of the stiffness is a multiple of the error on the measured frequencies. This multiplication factor decreases for more sensitive modes. In this experiment, the results are accurate enough to reflect the asymmetric weakening imposed upon the tibia. Attempts are made towards automatization of the measurement and analysis in order to get a system for clinical use. The actual system is still too cumbersome and time consuming for standard clinical use.

Humans↗
PubMed1986

Assessment of tibial stiffness by vibration testing in situ--I. Identification of mode shapes in different supporting conditions.

Vibrational methods to monitor fracture healing, the BRA and the IFR, are compared under different supporting conditions, excitation technique and signal processing. Mode shapes are identified by modal analysis. A wet excised human tibia and an amputation specimen are investigated. Excitation technique and signal processing caused only minor differences in the resonance frequencies. The supporting conditions had an important influence on the single bending modes changing both mode-shapes and frequencies. Thus the BRA-splint imposed a node at the malleolus. Modal analysis revealed the following modes in the two supporting conditions: BRA-splint: A 'rigid body' mode of 165 Hz in the sagittal plane. A single bending mode of 315 Hz close to the sagittal plane. IFR-hanging leg: A 'rigid-body' mode of 167 Hz close to the sagittal plane. Two single bending modes ('free-free'), a mode of 303 Hz close to the frontal plane and a mode of 470 Hz in the sagittal plane.

Biomechanical Phenomena↗
PubMed1986

Assessment of tibial stiffness by vibration testing in situ--II. Influence of soft tissues, joints and fibula.

The influence of soft tissues and joints on the vibration of the human tibia was examined by modal analysis on amputated lower limbs, where the soft tissues and the fibula were dissected gradually. Measurements were made in two different set ups, IFR and BRA, which were both designed to monitor fracture healing. In IFR, vibrations are generated by hammer impact on a relaxed hanging lower leg, with the knee flexed. Resonant frequencies are determined by a computer Fourier transform procedure. In BRA, a steady state vibration is induced in a lower leg, supported near the ankle and the tibial tuberosity, using an electromagnetic shaker. Resonant frequencies are determined from the maxima in vibration amplitudes. In both set ups the soft tissues have a similar influence on the vibration of the tibia: the skin hardly influences the determined modal parameter. The mass of the muscles influences both the resonant frequency and the damping. The fibula has a stiffening effect on the tibia. The influence of the joints is small in the IFR-set up: the tibia vibrates in conditions close to those for the free-free vibration. In the BRA-set up, the supports determine the boundary conditions.

Biomechanical Phenomena↗
PubMedDate not supplied

Dissociation of normal feature analysis and deficient processing of letter-strings in dyslexic adults.

Neuroimaging studies have revealed that the functional organization of reading differs between developmentally dyslexic and non-impaired individuals. However, it is not clear how early in the reading process the differences between fluent and dyslexic readers start to emerge. We studied cortical activity of ten dyslexic adults using magnetoencephalography (MEG), as they silently read words or viewed symbol-strings which were clearly visible or degraded with Gaussian noise. This method has previously been used to dissociate between analysis of local features and pre-lexical word processing in fluent adult readers. Signals peaking around 100 ms after stimulus onset and originating in the postero-medial extrastriate cortex were associated with increasing local luminance contrast in the noise patches. These early visual responses were similar in dyslexic and non-impaired readers. In contrast, the letter-string-specific responses peaking around 150 ms predominantly in the left inferior occipito-temporal cortex in fluent readers were undetectable in dyslexic readers. Thus, while the early visual processing seems intact in dyslexic adults, the pattern of cortical activation starts to differ from that of fluent readers at the point where letter-string-specific signals first emerge during reading.

Adult↗