Biomedical subjects

J Ivins

Publications and source records attributed to J Ivins.

3 recordsLinked to original sources

PubMed1999

The 'ecological' probability density function for linear optic flow: implications for neurophysiology.

A theoretical analysis of the recovery of shape from optic flow highlights the importance of the deformation components; however, pure deforming stimuli elicit few responses from flow-sensitive neurons in the medial superior temporal (MST) area of the cerebral cortex. This finding has prompted the conclusion that MST cells are not involved in shape recovery. However, this conclusion may be unjustified in view of the emerging consensus that MST cells perform nonlinear pattern matching, rather than linear projection as implicitly assumed in many neurophysiological studies. Artificial neural models suggest that the input probability density function (PDF) is crucial in determining the distribution of responses shown by pattern-matching cells. This paper therefore describes a Monte-Carlo study of the joint PDF for linear optic-flow components produced by ego-motion in a simulated planar environment. The recent search for deformation-selective cells in MST is then used to illustrate the importance of the input PDF in determining cell characteristics. The results are consistent with the finding that MST cells exhibit a continuum of responses to translation, rotation, and divergence. In addition, there are negative correlations between the deformation and conformal components of optic flow. Consequently, if cells responsible for shape analysis are present in the MST area, they should respond best to combinations of deformation with other first-order flow components, rather than to the pure stimuli used in previous neurophysiological studies.

Eye Movements↗

PubMed1992

Anger, depression and self-concept in adults with mental retardation.

Self-report measures of anger, depression and self-concept that were designed for non-retarded children were adapted for adults with mental retardation. The measures were administered to 130 adults with mental retardation who lived in the community. Informants rated the subjects on shortened forms of the three emotional indices. Informant self-concept ratings were negatively correlated with ratings of anger and depression. On the self-report measures, subjects who reported low self-concept also reported high levels of depression. Mildly mentally retarded subjects were more likely to report anger than severe/moderately retarded subjects. Informant and self-report measures were significantly correlated for self-concept and depression, but not for anger. The results provide preliminary normative data on indices of emotional adjustment for community-based adults with mental retardation.

Activities of Daily Living↗

PubMedDate not supplied

A semiautomatic tool for 3D medical image analysis using active contour models.

We describe a computerized tool designed to improve the efficiency with which clinicians can delineate volumes of interest in multi slice medical data such as NMR and CT images. The tool allows a trained user to create deformable models that can be used to search for edges or regions. Models can also be copied from previously analysed images into fresh slices, and frozen so they can only translate, rotate and scale, without deforming. In this way an accurate model can be used to extract an object from several adjacent slices. Surfaces are then reconstructed from the models using conic splines. By applying these techniques to objects such as tumours, it should be possible to generate three-dimensional images that are accurate enough to use when planning surgery and radiotherapy.

Animals↗