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N Foreman

Publications and source records attributed to N Foreman.

At least 19 recordsLinked to original sources
PubMed2006

The threshold signal:noise ratio in the perception of fragmented figures.

Perception thresholds were measured for fragmented outline figures (the Gollin test). A new approach to the question of the perception of incomplete images was developed. In this approach, figure fragmentation consisted of masking with multiplicative texture-like noise--this interference was termed "invisible" masking. The first series of studies established that the "similarity" between the amplitude-frequency spectra of test figures and "invisible" masks, expressed as a linear correlation coefficient, had significant effects on the recognition thresholds of these figures. The second series of experiments showed that progressing formation of the figures was accompanied by increases in the correlation between their spatial-frequency characteristics and the corresponding characteristics of the incomplete figure, while the correlation with the "invisible" mask decreased. It is suggested that the ratio of the correlation coefficients, characterizing the "similarity" of the fragmented figure with the intact figure and the "invisible" mask, corresponds to the signal:noise ratio. The psychophysical recognition threshold for figures for naive subjects not familiar with the test image alphabet was reached after the particular level of fragmentation at which this ratio was unity.

Adolescent↗
PubMed2005

The optical-geometrical characteristics and thresholds of perception of fragmented outline figures.

Measurements were made of the threshold of recognition of cumulatively forming line figures. The threshold value of the outline, expressed in pixels, depended on the length of the outline of the whole unfragmented figure. Relative threshold values were constant, and for the measures of figure fragments used in the present study, averaged 12.5%. A spatial frequency analysis of the test images was performed. Variation of the amplitude-frequency parameters of the spectra of the images of various figures with threshold fragmentation was minimal as compared with the variation of these parameters in figures with subthreshold or suprathreshold levels of fragmentation.

Adolescent↗
PubMed2004

[Signal/noise ratio at the visual recognition threshold of incomplete figures].

We measured recognition thresholds of incomplete figure perception (the Gollin test). This test we regarded as a visual masking problem. Digital image processing permits us to measure the spatial properties and spatial frequency spectrum of the absent part of the image as the mask. Using a noise paradigm, we have measured the signal/noise ratio for Incomplete Figure. Recognition was worse with better spectral "similarity" between the figure and the "invisible" mask. At threshold, the spectrum of the fragmented image was equally similar to that of the "invisible" mask and complete image. We think the recognition thresholds for Gollin stimuli reflect the signal/noise ratio.

Adolescent↗
PubMed2003

[Optical-geometrical parameters and perception threshold of the fragmented contour figures].

The thresholds of recognition of line drawings of common objects were measured using the Gollin-test procedure, in which separate random line fragments are displayed cumulatively up to the point of recognition. It was shown that the mean percentage of contour displayed at threshold recognition for different images was always about 12.5%, despite inter-subject variability between 5% and 25%. The comparative and spatial-frequency analysis of the geometrical parameters of images was carried out for different levels of fragmentation (before threshold, at threshold, and for the complete contour). The magnitude information of the Fourier domain image of figures was characterized by maximum at low and high levels of fragmentation, but at recognition threshold fragmentation it was characterized by minimum variability.

Adolescent↗
PubMed2001

Diffuse, retroperitoneal mesenteric and intrahepatic periportal plexiform neurofibroma in a 5-year-old boy.

We present a case of plexiform neurofibroma involving the retroperitoneum, mesentery, and liver in a 5-year-old boy who underwent evaluation for extent of a palpable left neck mass. The mass had intrathoracic extension with great vessel encasement and extension into the abdomen. Abdominal CT revealed a diffuse low-attenuation non-enhancing mass encasing the retroperitoneal vessels with serpiginous extension into the liver along the portal vein. This spread pattern of plexiform neurofibroma is an unusual manifestation of neurofibromatosis in a young child.

Child, Preschool↗
PubMed2000

Spatial information transfer from virtual to real versions of the Kiel locomotor maze.

The Kiel locomotor maze requires participants to choose five targets from among 20 locations marked by small red lights on the floor of a dimly lit circular environment having four wall-mounted extramaze cues and two intramaze cues at floor level. In the present study, acquisition of the real task was examined in 11-year-old children following prior accurate training in a virtual version, following misleading virtual training, or following no training. The virtual version was displayed on a desk-top computer monitor. Acquisition testing in the real maze was either locomotor or non-locomotor. Good transfer was achieved from virtual to real versions. Children's exploration of the real maze prior to real maze acquisition training revealed a clear transfer of spatial information previously learned in the virtual version. Children taught the correct target configuration in the simulation made fewer errors and more rapid, confident responses to targets in the real maze than children given no training. However, acquisition was also better following misleading training than no training, suggesting that a non-specific components of performance also transferred. Male superiority was only seen following misleading training, which was interpreted in terms of male superiority in mental rotation. After acquisition, a single probe trial was performed, in which proximal cues and participants' starting position were rotated, but this had equivalent effects on all groups' performance. It is clear that transfer of spatial information occurs from the simulated Kiel maze to the real version. This has implications for its use in diagnosis and training.

Child↗
PubMed1999

Chemotherapy for intracranial ependymomas.

Chemotherapy has been used extensively in the management of children with intracranial ependymoma. In this review, we discuss the results of phase II studies and clinical trials conducted in newly diagnosed and recurrent ependymomas. There is little evidence that chemotherapy is effective in this tumour. The response rate to single agents is 11%, with less than 5% complete responses, cisplatin being the most active agent in phase II studies. Combinations may be more effective, although the response rate with high-dose regimens is disappointing. Early results of protocols conducted in infants and young children do not suggest that chemotherapy is beneficial. A more rigorous assessment of chemotherapy is required in order to define its role in patients with intracranial ependymomas. Indeed, it is difficult to justify the use of chemotherapy outside such studies. More large studies, perhaps intergroup, limited to children with ependymomas would be of particular value.

Antineoplastic Agents↗
PubMed1998

Ki-67 immunolabelling index is a prognostic indicator in childhood posterior fossa ependymomas.

Conventional histological evaluation and subclassification of childhood ependymomas poorly predict their biological behaviour. The Ki-67 labelling index (Ki-67 LI), a measure of growth fraction, correlates with the biological behaviour of several neoplasms, and this retrospective study tested the hypothesis that Ki-67 LI is a prognostic indicator in childhood posterior fossa ependymomas. Immunocytochemistry using an antibody to Ki-67 was undertaken on 5 microns sections of formalin-fixed, paraffin-embedded tissue from 74 cases of childhood (age < 16 years.) posterior fossa ependymoma. A Ki-67 LI was established by counting the proportion of labelled nuclei in more than 1000 cells from several histological fields. Several clinical and histological variables (including Ki-67 LI) potentially associated with survival were entered into univariate and multivariate analyses using a Cox proportional hazards model. Variables that showed a significant and independent association with survival were Ki-67 LI (P < 0.002), whether total surgical resection had been achieved according to operation records (P < 0.03), and whether no adjuvant therapy had been given (P < 0.01). Age, sex, and the presence of necrosis or microvascular proliferation did not correlate with survival. In our defined population of patients with ependymomas, Ki-67 LI is a strong prognostic indicator. We recommend that Ki-67 LI is used in the histological evaluation of childhood posterior fossa ependymomas during trials of novel adjunctive therapies.

Adolescent↗
PubMed1998

A rejoinder.

Explore the source record for details and available documents.

Persons with Disabilities↗
PubMed1998

Uses of virtual reality in clinical training: developing the spatial skills of children with mobility impairments.

In this chapter we review some of the ways in which the skills learned in virtual environments (VEs) transfer to real situations, and in particular how information about the spatial layouts of virtual buildings acquired from the exploration of three-dimensional computer-simulations transfers to their real equivalents. Four experiments are briefly described which examined VR use by disabled children. We conclude that spatial information of the kind required for navigation transfers effectively from virtual to real situations. Spatial skills in disabled children showed progressive improvement with repeated exploration of virtual environments. The results are discussed in relation to the potential future benefits of VR in special needs education and training.

Computer Simulation↗
PubMed1997

Visual search, perception, and visual-motor skill in "healthy" children born at 27-32 weeks' gestation.

Visual-perceptual, attentional, and visual-motor skills were examined in a group of 16 school-age children, born at 27-32 gestational weeks, who had performed normally on pediatric screening tests. Compared with 16 matched full-term controls, the preterms performed poorly on only two measures: they took longer to point to the missing arc of an annulus displayed on a computer screen and failed to find targets more often in a complex visual search task. They showed no deficits on tests of visual form extraction and closure. These data suggest that in the absence of any disability that is clinically detectable, prematurity results in a cluster of small but significant visual-motor impairments that persist into middle childhood. These relate to the maintenance of attention and visual-motor coordination, though visual form perception is not measurably affected. The results are discussed in the context of current neurobiological models of visual system organization.

Analysis of Variance↗
PubMed1997

Virtual reality, disability and rehabilitation.

Virtual reality, or virtual environment computer technology, generates simulated objects and events with which people can interact. Existing and potential applications for this technology in the field of disability and rehabilitation are discussed. The main benefits identified for disabled people are that they can engage in a range of activities in a simulator relatively free from the limitations imposed by their disability, and they can do so in safety. Evidence that the knowledge and skills acquired by disabled individuals in simulated environments can transfer to the real world is presented. In particular, spatial information and life skills learned in a virtual environment have been shown to transfer to the real world. Applications for visually impaired people are discussed, and the potential for medical interventions and the assessment and treatment of neurological damage are considered. Finally some current limitations of the technology, and ethical concerns in relation to disability, are discussed.

Activities of Daily Living↗
PubMed1996

Effects of parietal cortex lesions on spatial problem solving in the rat.

The Maier 3-table task was used to examine spatial representations in rats with lesions of the parietal cortex. Some animals had anteriorly placed lesions, some posteriorly placed in cortical areas, sometimes regarded as 'parietal' in earlier studies. After 5 days of familiarization, animals were given 18 days of testing on the standard Maier task. Both parietal groups were initially impaired, but reached the same level of performance as controls by the end of the test period. Learning occurred both within and between sessions for the anterior group, but only between sessions for the posterior group. There was no major functional differentiation apparent on this task between the two 'parietal' areas. Rate of exploration increased in both parietal groups across test sessions as task performance improved. It is argued that the change in exploratory activity across sessions in parietal groups may reflect the adoption of a compensatory strategy which improved performance, but that improvement could also have been due to neural changes, as structures, such as the frontal cortex or hippocampus, assume some functions normally mediated by the parietal area.

Animals↗
PubMed1996

Transfer of spatial information from a virtual to a real environment in physically disabled children.

A group 10 severely physically disabled children explored a to-scale computer simulation of a real multi-storey building. Following exploration, their knowledge of the spatial properties of the real environment was assessed by asking them to point to fire apparatus that was not visible from the test site. Subjects in a control group were asked to complete the same assessment tasks, but without the opportunity to explore either the real building or the computer simulation. The estimates of the disabled children were superior to the control group indicating good transfer of spatial knowledge. Route finding and recognition reports provided support for the pointing data in indicating good transfer of spatial information.

Child↗
PubMed1995

Distractibility and locomotor activity in rat following intra-collicular injection of a serotonin 1B-1D agonist.

The superior colliculus (SC) is thought to be the decision center for reactions to novel and/or moving stimuli in the peripheral visual field. Serotonin 1B (5-HT1B) receptors were previously demonstrated to be located on collicular axon terminals of retinal ganglion cells and their activation might depress afferent inputs from the retina. The effects of intra-collicular injections of 5-HT1 drugs on distractibility were studied in hooded rats trained to run toward illuminated targets for a food reward in a 2-choice runway. 8-hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT), a 5-HT1A receptor agonist, RU 24969, a mixed 5-HT1A and 5-HT1B agonist, serotonin-O-carboxymethylglycyltyrosinamide (S-CM-GTNH2), a mixed 5-HT1B and 5-HT1D receptor agonist and saline (control) were alternately injected. Following the S-CM-GTNH2 treatment alone, animals exhibited an erratic running style, involving side-to-side movements of the head, without change in the overall accuracy of their locomotor trajectories, but with substantial decrease in their running speed. When distracting peripheral lights were introduced at the mid-points of the animals' run, in the weaker distracting condition (unilateral distractor) only, distraction indexes were found lower following the S-CM-GTNH2 treatment than following the other drug or saline treatments. It is concluded that serotonin, via 5-HT1B-1D receptors, may induce an elevation of the visual distractibility threshold by modulating directly the transmission of the primary visual signal.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1994

Choice autonomy and memory for spatial locations in six-year-old children.

Six-year-old children were presented with 12 identically labelled locations in a room and required to search non-redundantly for the six that contained rewards. On each day they could commit Across-Trial Memory (ATM) errors by visiting non-rewarded locations, or Within-Trial Memory (WTM) errors by revisiting locations previously visited that day. Groups were trained for nine days, either walking or pushed in a wheelchair, and with or without freedom of choice. They were then tested, walking with freedom of choice. Performance of the task improved significantly across training days in groups allowed free choice, whether walking or transported, and was superior at test to that of non-choosing groups. Throughout training and testing, the ATM component of performance was superior in groups allowed free choice. WTM was more accurate than would be expected by chance in all subjects at all stages of the experiment, but did not differ between groups. The problem of comparing WTM scores in groups differing in ATM accuracy was discussed. It was concluded that the primary benefit of free choice in spatial memory tasks is that it promotes accurate environmental segmentation, and that WTM is little affected by training or environmental familiarity.

Child↗
PubMed1994

Immunomodulatory effects of human neuroblastoma cells transduced with a retroviral vector encoding interleukin-2.

We have investigated whether retroviral mediated transfer of the IL-2 gene renders human neuroblastoma cells immunogenic, justifying their use in a clinical tumor immunization study. Fourteen neuroblastoma cell lines were established from patients with disseminated neuroblastoma and transduced with the vector G1Ncvl2, which contains the neomycin phosphotransferase gene and the cDNA of the human interleukin-2 gene. Clones secreting > 150 pg/10(6) cells/24 h of IL-2 were selected for further study. Secretion of IL-2 was maintained for at least 3 weeks in nonselective media, implying that production of the cytokine would continue under in vivo conditions. Co-culture of IL-2 transduced cell lines with patient lymphocytes induced potent cytotoxic activity against both transduced and parental neuroblastoma cell lines. This activity was HLA unrestricted, and predominantly mediated by CD16+ or CD56+ and CD8- lymphocytes. These data form the preclinical justification for our current immunization protocol for patients with relapsed or resistant neuroblastoma.

Antibodies, Monoclonal↗