Biomedical subjects

J Rivest

Publications and source records attributed to J Rivest.

22 records · Page 2Linked to original sources

PubMed1989

Transient anosognosia for episodic hemiparesis: a singular manifestation of TIAs and epileptic seizures.

Anosognosia is a well-known manifestation of non-dominant parietal lobe lesions and typically lasts a few days. That anosognosia may last only a few minutes to a few hours, as observed in six patients, has not been reported. In five patients, transient anosognosia for equally brief left-sided hemiparesis was a manifestation of transient ischemic attacks (TIAs). In the sixth patient, anosognosia for both a left-sided motor seizure and a subsequent brief left hemiparesis could best be explained by an epileptic ictal and post-ictal transient dysfunction of the non-dominant parietotemporal cortex. Prompt recognition of transient anosognosia, whether ischemic or epileptic, is mandatory for proper diagnosis and for rapid initiation of specific therapy.

Aged↗

PubMed1989

The roles of convergence and apparent distance in depth constancy with motion parallax.

The question of whether motion parallax is calibrated by convergence or by apparent distance for depth perception was addressed in three experiments. In Experiment 1, a random dot parallactic display was viewed monocularly at a distance of 80 cm, and the convergence angles were set for distances of 40, 60, and 80 cm. Averaged apparent depth was not different across conditions. In Experiment 2, a display consisting of one surface showing dollar bills and one surface showing random dots was viewed monocularly at a distance of 80 cm. It was presented at two different apparent distances, which were manipulated by varying the size of the dollar bills. In one condition, normally sized dollar bills were presented, and in another condition, the size was reduced by 30%. The averaged apparent depth associated with the small-bill display was larger than the depth associated with the normally sized bill display. In Experiment 3, a random dot display was viewed monocularly at 120 cm. In the primary condition, the random dot display was viewed with an induction screen at 80 cm, and it was moved from side to side such that it appeared stationary and close to the plane of the induction screen. In a comparison condition, the display was viewed without the induction screen and was moving from side to side at 120 cm. In another comparison condition, the display was again viewed without the induction screen but was stationary at 120 cm. Observers adjusted the extent of motion parallax so that apparent depth was 1 cm. The mean extent of parallax was larger in the primary conditio.(ABSTRACT TRUNCATED AT 250 WORDS)

Accommodation, Ocular↗

PubMed1986

Depth perception as a function of motion parallax and absolute-distance information.

The results of three experiments demonstrated that the visual system calibrates motion parallax according to absolute-distance information in processing depth. The parallax was created by yoking the relative movement of random dots displayed on a cathode-ray tube to the movements of the head. In Experiment 1, at viewing distances of 40 cm and 80 cm, observers reported the apparent depth produced by motion parallax equivalent to a binocular disparity of 0.47 degree. The mean apparent depth at 80 cm was 2.6 times larger than at 40 cm. In Experiment 2, again at viewing distances of 40 cm and 80 cm, observers adjusted the extent of parallax so that the apparent depth was 7.0 cm. The mean extent of parallax at 80 cm was 31% of that at 40 cm. In Experiment 3, distances ranged from 40 cm to 320 cm, and a wide range of parallax was used. As distance and parallax increased, the perception of a rigid three-dimensional surface was accompanied by rocking motion; perception of depth was replaced by perception of motion in some trials at 320 cm. Moreover, the mean apparent depths were proportional to the viewing distance at 40 cm and 80 cm but not at 160 cm and 320 cm.

Cues↗

PubMed1985

HLA system, body fat and fat distribution in children and adults.

The association between the genotypes and the alleles at the A, B or C locus of the HLA system and body fat was studied in a total of 1578 individuals subdivided in four cohorts: adult males (n greater than or equal to 204), adult females (n greater than or equal to 184), boys and male adolescents (n greater than or equal to 282), and girls and female adolescents (n greater than or equal to 257). None of these subjects were grossly obese or had known metabolic disorders. Percent body fat from underwater weighing, subcutaneous fat from 6 skinfold measurements, trunk fat (3 skinfolds) and extremity fat (3 skinfolds) were considered in the analysis. Although a few significant associations were encountered, the lack of consistency across samples suggested that they were probably random and biologically not meaningful. The same negative findings were found for the ratio of trunk subcutaneous fat to extremity subcutaneous fat and the ratio of subcutaneous fat (6 skinfolds) to total fat mass. Earlier reports indicating a significant association between high body fat content and antigens B18, Bw35 or Cw4 were not supported by the results of this study. It was concluded that no consistent pattern of association emerged between genotypes or alleles of the HLA system and percent body fat, subcutaneous fat or fat distribution in children and adults of both sexes.

ABO Blood-Group System↗