Search PubMed⌕ Search

Biomedical subjects

P J Bennett

Publications and source records attributed to P J Bennett.

At least 37 records · Page 2Linked to original sources
PubMed1998

Development and validation of a questionnaire designed to measure foot-health status.

The aim of this study was to apply the principles of content, criterion, and construct validation to a new questionnaire specifically designed to measure foot-health status. One hundred eleven subjects completed two different questionnaires designed to measure foot health (the new Foot Health Status Questionnaire and the previously validated Foot Function Index) and underwent a clinical examination in order to provide data for a second-order confirmatory factor analysis. Presented herein is a psychometrically evaluated questionnaire that contains 13 items covering foot pain, foot function, footwear, and general foot health. The tool demonstrates a high degree of content, criterion, and construct validity and test-retest reliability.

Adult↗
PubMed1997

Depressive symptoms and alterations in sucrose taste perception: cognitive bias or a true change in sensitivity?

Previous studies have reported elevated taste thresholds in depressed subjects, but those studies did not control for changes in response bias. The current study used signal detection analyses to address this shortcoming. Sucrose detection thresholds were measured (1) in subjects with high and low Hamilton Depression Rating Scale (HAM-D) scores who did not meet standard criteria for current Major Depressive Episode (MDE); and (2) in subjects who did fulfil standard criteria for MDE. Subjects with low HAM-D scores produced significantly more false alarms than the other two groups, but taste sensitivity, as indexed by d', did not vary significantly across groups. These results suggest that changes in response bias underlie previously reported increases in sucrose taste thresholds in depressed subjects.

Adult↗
PubMed1996

Masking of spatial frequency in visual memory depends on distal, not retinal, frequency.

Spatial frequency discrimination thresholds measured in a two-interval forced choice paradigm are virtually constant across inter-stimulus intervals ranging from 400 to 30,000 msec, demonstrating that an accurate representation of spatial frequency is maintained in short-term memory. This representation can be degraded by briefly flashing a grating during the retention interval. Moreover, this memory masking effect varies with the spatial frequency of the mask, suggesting that the mechanisms used to store spatial frequency in memory are similar to low-level visual filters. In this paper we replicate those previous findings and extend them by showing (1) that accurate memory for spatial frequency lasts as long as 1 min; (2) that memory masking is based on distal (c/cm), not retinal (c/deg), spatial frequency.

Differential Threshold↗
PubMed1996

The influence of membrane cholesterol on the GABAA receptor.

1. Neurosteroids such as pregnanolone have been established as potent modulators of the GABAA receptor in both electrophysiological and binding studies. Since cholesterol is present in substantial amounts in the neuronal membranes, we have sought evidence for possible interactions of cholesterol with the neurosteroid site and more generally, with the GABAA channel. 2. Synaptosomal membranes were prepared from rat whole brain, cerebral cortex, cerebellum and spinal cord. These membranes were enriched with cholesterol to about double the original level by incubation with liposomes comprised of 50 phosphatidylcholine: 50 cholesterol in the presence of 1% BSA. The additional cholesterol formed a homogeneous mixture with the endogenous cholesterol. 3. The effects of cholesterol and modulatory drugs on the GABAA channel were assessed from the changes induced in [3H]-flunitrazepam (FNZ) binding. Cholesterol enrichment did not affect FNZ binding itself; however, the enhancement of [3H]-FNZ binding by pregnanolone was affected. In membranes from cerebral cortex, the potency of pregnanolone was reduced by a factor of 3.2 following cholesterol enrichment. By contrast, in membranes from spinal cord, the potency of pregnanolone was increased by a factor of 8.4 following cholesterol enrichment. In membranes from cerebellum, there was little overall change in pregnanolone potency although the effects of threshold concentrations were increased. 4. The enhancement of [3H]-FNZ binding by propofol in whole brain membranes was reduced in cholesterol-enriched membranes, similar to the effects of pregnanolone. Experiments with muscimol resulted in an increase in its potency as a potentiator of [3H]-FNZ binding, following cholesterol enrichment. 5. These results provide little evidence for a selective competition between cholesterol and pregnanolone at its binding site. Rather, they suggest an influence of membrane cholesterol on the functional coupling between the benzodiazepine site and the other specific drug sites on the GABAA channel. The detailed pattern of influence depended upon the region of CNS and may be related to the subunit composition of the GABAA channels present.

Animals↗
PubMed1996

Spatial phase differences can drive apparent motion.

Can shape differences drive apparent motion? Results from previous research are equivocal. Much of the confusion may be due to the use of relatively complex stimuli: letters or geometric shapes, comprising many spatial frequencies, phases, orientations, and contrasts. We focus on relatively simple stimuli: Gaussian damped f+nf compound sinewave gratings. We examine whether relative phase differences, which are critical for shape perception, can drive apparent motion. We find that some, but not all, phase differences can drive apparent motion. Specifically, stimuli that are easily discriminable and perceptually dissimilar can affect the solution of the correspondence problem. In this case, observers consistently perceive stimuli in one frame moving to the position of perceptually similar stimuli in the next frame. This general result holds over a wide range of spatial frequencies, orientations, and contrasts. Implications for theories of motion processing are discussed.

Attention↗
PubMed1996

Analysis of risk factors for neuropathic foot ulceration in diabetes mellitus.

Diabetes mellitus affects about one in 25 Australians. Neuropathic foot ulceration is a frequent complication in persons with diabetes. This study evaluates the importance of different risk factors for the development of this condition. The role of nonenzymatic glycosylation and pressure beneath the sole of the foot in the pathogenesis of neuropathic foot ulcers was investigated. Twenty-seven subjects with diabetes with a recent history of neuropathic foot ulceration were matched by age and sex with a group of 50 control subjects without neuropathy or history of foot ulceration. The degree of nonenzymatic glycosylation was assessed by analyzing the average level of glycosylated hemoglobin in the 3 years prior to the development of the foot ulcer and a goniometer assessment of peripheral joint (hand and ankle) flexibility. Dynamic pressure of the plantar aspect of the foot was recorded using a Musgrave Footprint System pedobarograph during a normal gait cycle. There was no significant difference in age, sex, body mass index, and duration or type of diabetes between the ulcer and control groups. The pressure of the plantar aspect of the foot was significantly elevated (p < 0.01). Ankle joint flexibility was reduced (p < 0.01) in cases with neuropathic foot ulceration compared with the control group. There was a trend toward elevation of glycosylated hemoglobin (HbA1c fraction) or HbA1c in the ulcer group (p = 0.06). The results suggested that nonenzymatic glycosylation occurs at a more significant level in patients with diabetes with a history of neuropathic foot ulceration.

Aged↗
PubMed1995

Letter localization, not discrimination, is constrained by attention.

Shaw (1984; Shaw, Mulligan & Stone, 1983) measured the probability of detecting a target letter in displays containing different numbers of items. The set size effect was significantly larger than the effect predicted by unlimited-capacity models of visual processing, and Shaw concluded that attention constrains the discrimination of complex, but not simple, patterns. We re-examined the role of attention in letter discrimination by measuring the effect of set size on the contrast needed to identify a target embedded among distractors. The results of 5 experiments show that set size effects are small for letter discrimination, but large for letter localization. The findings suggest that the large set size effect reported by Shaw (1984) was a result of asking subjects to localize the target. In addition, the results are consistent with the hypothesis that limited processing capacity constrains the perceptual processes involved in letter localization, but not discrimination.

Attention↗
PubMed1994

Classification and perceived similarity of compound gratings that differ in relative spatial phase.

Discrimination studies suggest that two, and only two, channels encode relative spatial phase shifts in compound gratings (Bennett & Banks, 1991; Field & Nachmias, 1984). The more sensitive channel consists of even-symmetric filters and responds best to cosine phase shifts (e.g., 0 degree-180 degrees); the other consists of odd-symmetric filters and responds best to sine phase shifts (e.g., 90 degrees-270 degrees). The present experiments investigated whether the two-channel model generalizes to suprathreshold perceptual tasks. Experiment 1 examined classification learning of compound gratings, consisting of a fundamental (f) and second harmonic (2f), that differed in 2f contrast and relative phase. Experiments 2 and 3 measured the perceived similarity of f + 2f gratings. The results of Experiment 1 were broadly consistent with the predictions of the two-channel model. Specifically, the classification data were best explained by assuming that classification was based on the responses of differentially sensitive even- and odd-symmetric filters. In Experiments 2 and 3, two-dimensional multidimensional scaling solutions provided a good account for the similarity judgments. In Experiment 2, Dimension 1 was strongly correlated with cosine phase, and Dimension 2 was moderately correlated with sine phase. In Experiment 3, cosine phase was again strongly related to Dimension 1, whereas the absolute value of sine phase was strongly related to Dimension 2. Overall, these results suggest that the two-channel model of phase discrimination provides a useful framework for interpreting classification and similarity judgments of compound gratings.

Adult↗
PubMed1993

The harmonic bandwidth of phase-reversal discrimination.

Previous studies have shown that 180 degrees relative phase shifts in f + 2f gratings are discriminated when the cosine or the sine component of the shift exceeds some criterion (Bennett & Banks, 1987; Field & Nachmias, 1984). The current experiments demonstrate that this result holds for other two-component gratings, provided that the components are within two to three octaves of each other. For frequency differences greater than two to three octaves, phase-reversal discrimination is impossible. A simple model that discriminates phase shifts on the basis of changes in the responses of even- and odd-symmetric spatial filters can account for the results.

Contrast Sensitivity↗
PubMed1993

Pressure distribution beneath the human foot.

A descriptive study was undertaken to establish the 95 percentile limits (proposed normal reference range) for pressure beneath the hallux, metatarsal heads, and heel in a group of healthy adult subjects. A new force plate device capable of accurately measuring discrete areas of pressure beneath the human foot with high temporal and spatial resolution was used. The system is capable of accurately measuring plantar foot pressure during dynamic and static foot function. The results of this research are in close agreement with other published studies of plantar foot pressure measurement with comparable systems.

Adult↗
PubMed1992

The effects of luminance on FPL and VEP acuity in human infants.

Grating acuity was measured in 16-week-old human infants. Three measurement techniques were used: forced-choice preferential-looking (FPL), and two visual-evoked-potential (VEP) techniques. The stimuli were counterphase flickering sinewave gratings with a space-average luminance of -1.0 or 2.0 log cd/m2. Slightly different luminance-dependent changes occur between FPL and VEP acuities, suggesting that some factor influences the two methods differently as stimulus luminance varies. A comparison between FPL acuities and VEP acuities within infants suggests a quantitative relationship between techniques. Infant's acuity for sinewave gratings with a space-average luminance of -2.0, -1.0, 0.0, 1.0 and 2.0 log cd/m2 was also measured using a single VEP paradigm. The results are compared to the same measurements in adults and to infant and adult ideal observers. VEP acuity in this group of infants improves by about 0.5 log units between -2.0 and 0.0 log cd/m2 and remains asymptotic between 0.0 and 2.0 log cd/m2. This result suggests that luminance-dependent changes in infant acuity cannot be fully accounted for by immaturities in the optics and photoreceptor spacing and efficiency.

Evoked Potentials, Visual↗
PubMed1992

Cold fingers in leprosy.

Under conditions of maximal thermoregulatory peripheral dilatation, most healthy subjects (both Indian and European) showed raised blood flow in the fingertips (measured by laser Doppler flowmetry) where the skin temperature is only slightly lower than the core body temperature. Most borderline lepromatous (BL) leprosy patients had much colder fingers and the blood flow was slow: borderline tuberculoid (BT) patients had skin temperatures similar to those seen in healthy subjects, but their fingertip blood flow was reduced relative to that in control subjects. The occurrence of cold fingers and slow blood flow was clearly associated with evidence of sensory impairment to light touch, pressure and temperature. Slower fingertip blood flow was strongly associated with impairment of vasomotor control in this anatomical region, suggesting that both may be a consequence of leprosy peripheral neuropathy, at least in patients with early leprosy, but it is likely that leprosy arteriopathy may contribute to the lowered peripheral perfusion in advanced cases. It is suggested that the simple clinical sign of cold fingers may be of value in the preliminary assessment of patients presenting at any leprosy control clinic in the tropics.

Adult↗
PubMed1991

The effects of contrast, spatial scale, and orientation on foveal and peripheral phase discrimination.

We examined the effects of contrast, spatial scale, and orientation, on phase discrimination thresholds. In expt I, the ratio of thresholds for 180 deg shifts in F + 2F gratings remained invariant across a wide range of fundamental contrasts. Experiment II demonstrated that random fluctuations in overall pattern contrast did not affect discrimination. Experiment III found that foveal, but not peripheral, thresholds were roughly independent of spatial scale; foveal-peripheral differences in phase sensitivity could not be eliminated by scaling stimulus size. Finally, expt IV found that thresholds for some phase shifts varied significantly with orientation in the periphery; in general, peripheral sensitivity was greatest for radially-oriented gratings. The implications of these findings for models of phase discrimination are discussed.

Adult↗
PubMed1988

Optical and photoreceptor immaturities limit the spatial and chromatic vision of human neonates.

We examine the contributions of preneural mechanisms, i.e., the optics of the eye and the aperture, spacing, and efficiency of foveal cones, to poor spatial and chromatic vision in human neonates. We do so by comparing the performances of ideal observers incorporating the characteristics of the optics and the foveal cones of adults and neonates. Our analyses show that many, but not all, of the differences between neonatal and adult contrast sensitivities and grating acuities can be explained by age-related changes in these factors. The analyses also predict differing growth curves for vernier and grating acuities. Finally, we demonstrate that preneural mechanisms constrain chromatic discrimination in human neonates and that discrimination failures may reflect poor visual efficiency rather than immature chromatic mechanisms per se.

Aging↗
PubMed1987

The physical limits of grating visibility.

We examined the extent to which pre-neural factors constrain the detectability of sinusoidal gratings of different spatial frequencies and luminances. Contrast sensitivity functions were measured in two observers for foveally-presented grating patches. Spatial extent of the patches was inversely proportional to grating frequency. The observers' contrast sensitivity functions were then compared to the performance of an ideal discriminator (Geisler, 1984) which incorporated the effects of quantal fluctuations, optical transfer, ocular media transmittance, and the aperture, quantum efficiency, and spatial distribution of foveal photoreceptors. The sensitivity of the ideal discriminator was roughly 20-fold greater than that of the human observers, but the shapes of the ideal and human CSFs were quite similar from 5 to 40 c/deg and from 3.4 to 340 cd/m2. The similarity of shapes demonstrates that the high-frequency rolloff of the foveal CSF for gratings with a fixed number of cycles can be explained by the operation of pre-neural factors alone. Previous research has shown that grating summation area is inversely proportional to the square of spatial frequency. Thus, for gratings with fixed spatial extent the high-frequency rolloff can be explained by the pre-neural factors plus variations in grating summation area. These conclusions imply in turn that the neural transfer function is much flatter than previously thought and that private line connections from foveal photoreceptors to higher visual centers are common.

Eye Movements↗
PubMed1981

The performance characteristics of an intra-arterial oxygen electrode.

The performance characteristics of intravascular oxygen electrodes used during and after open heart surgery are described. The pO2 recorded continuously by the electrodes correlated extremely well with corresponding measurements made on samples of arterial blood. The results show that intravascular pO2 electrodes are accurate and can be readily used during surgery and intensive care of adult patients.

Adult↗