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Biomedical subjects

P J Hancock

Publications and source records attributed to P J Hancock.

7 recordsLinked to original sources
PubMed1998

A comparison of two computer-based face identification systems with human perceptions of faces.

The performance of two different computer systems for representing faces was compared with human ratings of similarity and distinctiveness, and human memory performance, on a specific set of face images. The systems compared were a graph-matching system (Lades M, Vorbrüggen JC, Buhmann J, Lage J, von der Malsburg C, Würtz RP, Konen W. IEEE., Trans Comput 1993;42:300-311.) and coding based on principal components analysis (PCA) of image pixels (Turk M, Pentland A. J Cognitive Neurosci 1991;3:71-86.). Replicating other work, the PCA-based system produced very much better performance at recognising faces, and higher correlations with human performance with the same images, when the images were initially standardised using a morphing procedure and separate analysis of 'shape' and 'shape-free' components then combined. Both the graph-matching and (shape + shape-free) PCA systems were equally able to recognise faces shown with changed expressions, both provided reasonable correlations with human ratings and memory data, and there were also correlations between the facial similarities recorded by each of the computer models. However, comparisons with human similarity ratings of faces with and without the hair visible, and prediction of memory performance with and without alteration in face expressions, suggested that the graph-matching system was better at capturing aspects of the appearance of the face, while the PCA-based system seemed better at capturing aspects of the appearance of specific images of faces.

Adult↗
PubMed1996

Face processing: human perception and principal components analysis.

Principal components analysis (PCA) of face images is here related to subjects' performance on the same images. In two experiments subjects were shown a set of faces and asked to rate them for distinctiveness. They were subsequently shown a superset of faces and asked to identify those that had appeared originally. Replicating previous work, we found that hits and false positives (FPs) did not correlate: Those faces easy to identify as being "seen" were unrelated to those faces easy to reject as being "unseen." PCA was performed on three data sets: (1) face images with eye position standardized, (2) face images morphed to a standard template to remove shape information, and (3) the shape information from faces only. Analyses based on PCA of shape-free faces gave high predictions of FPs, whereas shape information itself contributed only to hits. Furthermore, whereas FPs were generally predictable from components early in the PCA, hits appeared to be accounted for by later components. We conclude that shape and "texture" (the image-based information remaining after morphing) may be used separately by the human face processing system, and that PCA of images offers a useful tool for understanding this system.

Adult↗
PubMed1991

A statistical analysis of natural images matches psychophysically derived orientation tuning curves.

A neural net method is used to extract principal components from real-world images. The initial components are a Gaussian followed by horizontal and vertical operators, starting with the first derivative and moving to successively higher orders. Two of the components are 'bar-detectors'. Their measured orientation selectivity is similar to that suggested by Foster & Ward (Proc. R. Soc. Lond. B 243, 75 (1991] to account for brief-exposure psychophysical data. In tests with noise images, the ratio of sensitivity between the two components is controlled by the degree of anisotropy in the image.

Humans↗
PubMed1985

Physiologic and biochemical effects of ritodrine therapy on the mother and perinate.

The materno-fetal and neonatal effects of ritodrine were studied in 37 women treated for premature labor with intravenous (i.v.) ritodrine. Marked cardiovascular, respiratory, and biochemical side effects of therapy were seen in the mothers and tachycardia was noted in the fetuses. The neonates of 18 women in whom ritodrine successfully postponed delivery were delivered with good Apgar scores and their admission vital signs and nursery courses were benign. Ritodrine failed to delay delivery more than a week in 19 mothers. There were no differences between their newborns and 20 control neonates in admission vital signs, blood gases, blood chemistries, complete blood counts, platelet counts, peak bilirubin, or duration of oxygen therapy. This study revealed no deleterious effects on neonates delivered after maternal ritodrine therapy despite significant maternal and fetal effects.

Birth Weight↗
PubMed1984

Gastric motility in premature infants fed two different formulas.

The effect of two different formulas on gastric contractions was investigated in 10 preterm infants, of mean birth weight 1,149 g and mean gestational age 30.5 weeks, who were being advanced from a 20 calorie per ounce formula (Enfamil) to a 24 calorie per ounce formula (Similac Special Care 24). The neonates were fed by gravity with a feeding tube on a 2-h schedule. The orogastric tube was connected between feedings to a pressure transducer and recorder system upon which pressure waves reflecting gastric contractions were recorded. In the 1st h after feeding there were significantly fewer gastric contractions with 24 calorie than 20 calorie formula. The mean intensity of the gastric contractions per minute of contraction time was significantly less in the 1st h after feeding with the 24 calorie compared with the 20 calorie formula. In the 2nd h after feeding these values were similar. Gastric contractions are decreased with 24 calorie formula compared with 20 calorie formula during the 1st h after feeding. This difference in contractions may influence tolerance to different formulas.

Energy Intake↗
PubMed1983

Limitation of pulsatility index as a diagnostic tool in the newborn.

Pulsatile flow in the anterior cerebral arteries was studied and pulsatility index (PI) calculated by 3 observers in 10 newborn infants in order to establish the reproducibility of a noninvasive Doppler technique. No significant differences were noted among the observers and the estimated error of observation was 0.073. Subsequently, 14 healthy preterm infants were studied daily by a single observer in an attempt to establish a normal range of PI for prematures in the first 5 days of life. The babies were concomitantly studied with serial ultrasound examinations to rule out intracranial hemorrhage. The study revealed good interobserver reliability but wide variation of PI in normal, healthy premature infants with values falling within abnormal ranges previously described in asphyxiated infants or those with intraventricular hemorrhage (IVH). Caution is advised in using the PI to predict outcome.

Cerebral Arteries↗