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At least 577 records · Page 32Linked to original sources
PubMed1987

Phenylketonuria and complex spatial visualization: an analysis of information processing.

Recent neuropsychological studies have suggested that patients with early-treated phenylketonuria (PKU) and normal intelligence have a specific deficiency in solving complex spatial problems. In the present study a task involving the assembly of various shapes was used to compare the performance of 16 PKU patients and 11 sibling controls. Error rates generally were higher and response times slower among the PKU patients, but greater complexity did not produce differential changes in accuracy or speed in the PKU group compared to the controls. Correlations between task performance and IQ measures were significant for the PKU patients, but when IQ was controlled for the group differences vanished. The results suggest that choice of problem-solving strategy, attention span and accuracy of mental representation may be affected in PKU patients, despite efforts to maintain well-controlled phenylalanine concentrations in the blood.

Adolescent↗
PubMed1994

Electrophysiological correlates of feature analysis during visual search.

Event-related brain potentials (ERPs) were recorded from normal young adults during visual search tasks in which the stimulus arrays contained either eight identical items (homogeneous arrays) or seven identical items and one deviant item (pop-out arrays). Four experiments were conducted in which different classes of stimulus arrays were designated targets and the remaining stimulus arrays were designated nontargets. In Experiments 1 and 2, both target and nontarget pop-out stimuli elicited an enhanced anterior N2 wave and a contralaterally larger posterior P1 wave, but Experiments 3 and 4 demonstrated that these components do not reflect fully automatic pop-out detection processes. In all four experiments, target pop-outs elicited enlarged anterior P2, posterior N2, occipital P3, and parietal P3 waves. The target-elicited posterior N2 wave contained a contralateral subcomponent (N2pc) that exhibited a focus over occipital cortex in maps of current source density. The overall pattern of results was consistent with guided search models in which preattentive stimulus information is used to guide attention to task-relevant stimuli.

Adolescent↗
PubMed1958

X-ray visualization and analysis of multicomponent subjects.

The information carried by x-rays showing the distribution of each material of which a subject is assumed to be composed is distributed on separate films by means of a controlled variation in composition of the scanning radiation. The beam is modulated, for example, by simultaneous motion of several wedges. The method is useful in quantitative x-ray analysis and as a system for making radiographs predominantly sensitive to one material in the subject.

Humans↗
PubMed1962

Harmonic analysis of visual stimuli below fusion frequency.

Data which represent the relation between modulation amplitude and frequency of a sinusoidally modulated light stimulus for constant flicker appearance have been employed to predict characteristics of rectangular waveforms which will be of the same flicker appearance. Predictions are compared with the results of an experiment in which such rectangular waveforms were employed.

Flicker Fusion↗
PubMed1977

Mouse chromosome translocations: visualization and analysis by electron microscopy of the synaptonemal complex.

Pachytene chromosomes of mice heterozygous for known translocations are clearly depicted by configurations of the synaptonemal complexes in spread (whole mount) preparations. In one autosomal and two X-autosome translocations analyzed, breakpoints are identifiable; localization by measurement agrees with mitotic data and shows the translocations to be reciprocal. Synapsis with the Y is inhibited in one translocation in which the breakpoint is the pairing region of the X.

Animals↗
PubMed1997

Survival analysis and visual outcome in a large series of corneal transplants in India.

AIM/BACKGROUND: The public health significance of corneal transplantation in dealing with corneal blindness in the developing world would depend upon the survival rate of transplants. This study was done to analyse the survival rate of corneal transplants in a large series in India, and to evaluate the influence of various risk factors on transplant survival. METHODS: The records of a series of 1725 cases of corneal transplants carried out during 1987-95 at a tertiary eye care institution in India were reviewed. The Kaplan-Meier method was used to determine 5 year survival rates of corneal transplants performed for the various categories of preoperative diagnosis. Multivariate Cox proportional hazards regression was used to assess how preoperative diagnosis, socioeconomic status, age, sex, vascularisation of host cornea, quality of donor cornea, and training status of surgeon influenced transplant survival. The effect of these variables on visual outcome was assessed using multiple logistic regression. RESULTS: The survival rates at 1, 2, and 5 years for all corneal transplants performed for the first time in 1389 cases were 79.6% (95% confidence interval = 77.3-81.9%), 68.7% (65.7-71.7%) and 46.5% (41.7-51.3%). The 5 year survival rate was highest if the corneal transplant was done for keratoconus (95.1% (84.8-100%)) and lowest if carried out for previous transplant failure (21.2% (13.8-28.6%)). The relative risk of transplant failure was higher if the preoperative diagnosis was previous transplant failure (2.04 (1.62-2.55)), aphakic bullous keratopathy (1.78 (1.38-2.28)), corneal clouding due to miscellaneous causes including congenital conditions and glaucoma (1.63 (1.21-2.19)), or adherent leucoma (1.11 (0.81-1.51)) than for the other preoperative diagnoses. Patients with lower socioeconomic status had higher relative risk of transplant failure (1.28 (1.16-1.42)), as did patients < 10 years of age (1.42 (1.23-1.64)). Higher relative risk of transplant failure was associated with vascularisation of the host cornea before transplantation (1.15 (1.04-1.27)), and with the use of fair quality donor cornea for transplantation compared with excellent, very good, or good quality donor cornea (1.26 (1.06-1.52)). Before corneal transplant 80.2% of the eyes were blind (visual acuity < 3/60), whereas at last follow up 41.8% eyes were blind. The odds of having visual acuity > 6/18 were higher if the transplant was done for keratoconus (9.99 (6.10-16.36)) or corneal dystrophies (1.77 (1.21-2.58)) than for the other preoperative diagnoses. CONCLUSION: Reasonable success with corneal transplantation is possible in the developing world if data from this part of the world regarding the different survival rates for the various preoperative diagnoses and the influence of risk factors on transplant survival and visual outcome are taken into account while determining priority for transplant cases in the present situation of limited availability of donor corneas.

Adolescent↗
PubMed1989

Quantitative analysis of visual receptive fields of neurons in nucleus of the optic tract and dorsal terminal nucleus of the accessory optic tract in macaque monkey.

1. The visual receptive field properties of neurons in the nucleus of the optic tract (NOT) in the pretectum and the dorsal terminal nucleus (DTN) of the accessory optic tract were analyzed quantitatively in anesthetized, paralyzed macaque monkeys. 2. Visual latencies to reversals in direction of stimulus movement ranged from 40 to 80 ms [61 +/- 13.5 (SD) ms]. 3. All neurons increased their discharge rate during ipsiversive movement and decreased their ongoing activity during contraversive movement of single stimuli or whole-field random dot patterns. The population of neurons in the left NOT-DTN was excited most strongly by leftward movement pointing 4 degrees down; neurons in the right NOT-DTN were excited most strongly by rightward movement pointing 6 degrees down. The mean angle between the directions yielding the highest and the lowest discharge rate in the two populations of NOT-DTN neurons was 177 degrees. 4. The deviation of the preferred excitatory directions from the horizon in individual neurons varied with recording depth. Within the first 500 microns below the midbrain surface, neurons preferred near-horizontal directions, whereas neurons recorded more deeply preferred more oblique directions of stimulus movement. 5. The tuning widths of NOT-DTN neurons in the preferred excitatory direction were very broad. The mean halfwidth defined as the range of directions eliciting responses greater than 50% of the maximum was 127 +/- 25 degrees. 6. Moving a random dot pattern and a single bar of light simultaneously but in opposite directions caused NOT-DTN neurons to increase their discharge rate as soon as one of the two stimuli moved in the ipsiversive direction. The reduction in overall discharge rates when two stimuli moved in opposite directions indicates mainly inhibitory interactions. 7. All NOT-DTN neurons could be activated from both eyes. Interactions between the two eyes were modest and unspecific. Misalignment of the visual axes of the two eyes had no influence on response strength. 8. Optimal speeds of stimulus movement varied widely for different NOT-DTN neurons. The effective range of speeds to elicit direction-selective responses in the total population was very broad (0.1400 degrees/s. With oscillating horizontal stimulation, NOT-DTN neurons followed repetition rates up to 4 Hz at excursions of 40 degrees. Speeds greater than 500 degrees/s were either not effective or resulted in a suppression of ongoing activity in all directions of movement.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2006

Automatic analysis and visualization of microelectrode recording trajectories to the subthalamic nucleus: preliminary results.

Although microelectrode recordings (MER) are commonly used to confirm stereotactic targets during surgery for movement disorders, there is no consensus on whether the additional risks and cost of MER are worth the benefits. This may be due, in part, to the inconsistency and inefficiency of subjective interpretation of MER data that is currently used in practice. We describe several fully automatic visualization methods for MER that efficiently and clearly indicate segments of the microelectrode trajectories with homogeneous neural activity that correspond to expected deep brain nuclei. Specifically we demonstrate that these visualization methods can help identify the subthalamic nucleus in Parkinson's disease patients. These methods have the potential to significantly improve patient outcome by helping neurosurgeons objectively identify target structures more quickly and accurately.

Aged↗