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D M Parker

Publications and source records attributed to D M Parker.

At least 19 recordsLinked to original sources
PubMed1992

Temporal integration of spatially filtered visual images.

Factors which govern the temporal integration of spatial information were examined in a group of five experiments. A series of high-pass and low-pass spatially filtered versions of a visual scene were generated. Observers' ratings of these filtered versions of the scene for perceived image quality indicated that quality was determined both by the bandwidth of spatial information and the presence of high-spatial-frequency edge information. When sequences of three different versions of the scene were presented over an interval of 120 ms the perceived quality of the resulting composite image was determined both from the ratings of the individual components of that sequence and from the order in which these components were presented. When the order of spatial information in a sequence moved from coarse to fine detail the perceived quality of the composite image was significantly better than when the order moved from fine to coarse. This evidence of a coarse-to-fine bias in pattern integration was further investigated with a detection paradigm. The pattern of errors once again indicated that temporal integration of spatial information was superior when a coarse-to-fine mode of information delivery was employed. Taken together the data indicate that the pattern-integration mechanism has an inherent order bias and does not accumulate spatial information so efficiently when the 'natural' coarse-to-fine order is violated.

Attention↗
PubMed1992

Convergent and divergent perspective.

Use of divergent (or inverse) perspective in pictures is often regarded as arbitrary or even as erroneous in spite of the fact that entire schools of art exist in which this kind of perspective is regularly used. An experiment is reported which shows that a significant trend towards divergent perspective is experienced by subjects viewing laterally displaced three-dimensional arrays. Centrally viewed arrays show the expected perceptual convergence. It is therefore argued that divergent perspective, under appropriate conditions, is as perceptually legitimate an experience as convergent perspective.

Adult↗
PubMed1992

Apparent duration and spatial structure.

In three experiments, we investigated the relative perceived duration of a full bandwidth image and a set of high- and lowpass filtered images of a scene, briefly presented on a visual display unit. In Experiment 1, the various images were compared with each other, using a paired comparison method. All images were presented for 40 msec, and observers were asked to judge which of each pair of images had the longest duration. The results showed that images containing a wide spatial frequency bandwidth were judged to be of longer duration than were images of a narrower bandwidth, regardless of whether the latter were high- or lowpass filtered. In Experiment 2, a 40-msec presentation of each of the images was compared with a presentation of a probe that was 20, 40, 60, or 80 msec in duration. Observers again judged which of each pair of images had the longest duration. The results were very similar to those of Experiment 1, with wide bandwidth images being judged to be of longer duration than were narrow bandwidth images. In Experiment 3, instead of comparing the various filtered versions of the image with each other, we attempted to obtain a direct measure of perceived duration by comparing a flashing LED to a 40-msec flash of a subset of the images used in the previous experiments. The observers' task was to adjust the duration of the LED flash to match the perceived duration of each image.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Three-space inference from two-space stimulation.

Oblique contours sloping at 30 degrees with respect to the horizontal were presented alone, in combination to form chevrons, or with a vertical line to form arrowhead or Y patterns; they were projected onto a screen in the frontal parallel plane and viewed from positions that gave viewing angles of 90 degrees (normal to the screen's surface), 53 degrees, or 34 degrees. The perceived orientation of the contours, as assessed by a movable arm that the subjects set to be parallel to the obliques, changed monotonically as a function of viewing angle. The change was as great for single obliques as for combinations of obliques within the chevron, arrowhead, and Y patterns. The results of Experiment 1 were extended in Experiment 2, in which obliques at 30 degrees and 50 degrees with respect to the horizontal were presented singly or in combination as chevron patterns. It is argued that the results of both experiments indicate that single two-space oblique lines are immediately interpreted as lying in three-space and that the changes in perceived orientation are a consequence of this perceptual inference.

Adult↗
PubMed1991

Functional studies of a glutamate dehydrogenase with known three-dimensional structure: steady-state kinetics of the forward and reverse reactions catalysed by the NAD(+)-dependent glutamate dehydrogenase of Clostridium symbiosum.

Steady-state kinetic properties of glutamate dehydrogenase from Clostridium symbiosum are reported. Rates with NADP(H) are over three hundred times lower than with NAD(H) under identical conditions. The 3-acetyl pyridine and 6-deamino adenine analogues of NAD+, on the other hand, are used almost as well as NAD+ itself. Amino acid specificity is very tight at both pH 7 and pH 9. The best alternative substrate of those tested, L-alpha-amino-gamma-nitraminobutyrate, gave only 0.5% of the rate seen with glutamate. With 400 microM NAD+ a 160-fold variation of the glutamate concentration gave a linear Eadie plot apart from slight inhibition at the highest concentrations. With 40 mM L-glutamate and varied [NAD+], the Eadie plot appeared linear between 1.6 microM and 60 microM and again between 60 microM and 2000 microM, but the slopes of the two lines differed by a factor of 8.4. This striking pattern is not attributable to impurities in the coenzyme or to changes in the state of aggregation of the enzyme. For the high concentration range (greater than 60 microM NAD+), the presence of all four linear terms in the reciprocal form of the initial rate equation indicates a sequential mechanism. Similar measurements made for APAD+ and dnNAD+ show no sign of non-linearity in the Eadie plot over the wide concentration ranges explored. In the reductive amination direction, with NADH as coenzyme, linear reciprocal plots were obtained for all three substrates. Systematic variation of concentrations led via primary, secondary and tertiary plots to all eight possible initial-rate parameters in a linear reciprocal initial-rate equation. Compulsory-order and enzyme-substitution mechanisms appear to be excluded, and a random route to the central complex seems the only possibility compatible with the results.

Amines↗
PubMed1991

The Short NART: cross-validation, relationship to IQ and some practical considerations.

Beardsall & Brayne (1990) have presented a method whereby the full-length National Adult Reading Test (NART) scores of subjects who are of below average reading ability can be predicted from performance on the first half of the test (termed the Short NART). The accuracy with which the Short NART predicted full-length NART scores was examined in a large cross-validation sample (N = 674). A subgroup of this sample (N = 142) was administered the WAIS. The results indicated that the Short NART was only moderately successful in predicting full-length NART scores. However, comparison of the accuracy with which the full-length NART and Short NART predicted WAIS IQs, revealed that the superiority of the former was very minimal. It is concluded that, despite some reservations regarding the Short NART's practical utility, it can be used with reasonable confidence in clinical practice to estimate premorbid IQ.

Adolescent↗
PubMed1991

A synthesis of acylphosphonic acids and of 1-aminoalkylphosphonic acids: the action of pyruvate dehydrogenase and lactate dehydrogenase on acetylphosphonic acid.

Acylphosphonic acids, R-CO-PO(OH)2, have been synthesized by the steps [formula: see text] of which the last is new and provides a mild method for de-esterifying acylphosphonic acids. Their reductive amination gives a simple way of making 1-aminoalkylphosphonic acids. Acetylphosphonic acid inhibited NAD+ reduction by pyruvate with the pyruvate dehydrogenases from Escherichia coli and Bacillus stearothermophilus. The inhibition was competitive with pyruvate, with Ki of 6 microM for the E. coli enzyme (pyruvate Km 0.5 mM) and one of 0.4 mM of the B. stearothermophilus enzyme (pyruvate Km 0.1 mM). Acetylphosphonate and its monomethyl ester are substates for pig heart lactate dehydrogenase, with Km values of 15 mM and 10 mM respectively (pyruvate Km 0.05 mM) and specificity constants one thousandth that for pyruvate.

Acetaldehyde↗
PubMed1990

Intermittent alexia.

A case of intermittent alexia, sometimes accompanied by severe dysgraphia and sometimes by mild dysgraphia, which had a probable migrainous origin, is described. On some occasions the patient could write to dictation, although with many errors, while unable to read words or letters. On other occasions the patient's writing to dictation was seriously disordered in terms of content and the letters were produced clumsily. Reading of numbers, colour vision and colour naming were normal although impairments on right-left orientation and visual short term memory were present and a mild finger agnosia was apparent. Blood flow scans (SPECT) taken under normal and alexic conditions support the view that the disturbance had a vascular origin.

Adolescent↗
PubMed1990

Reaction time measures of feature saliency in schematic faces.

Two separate paradigms utilizing measurements of reaction time were employed to study facial feature saliency in schematic line drawn faces. In the first paradigm the speed of response to the omission of different facial components was measured, and in the second, the speed of response to feature substitution was measured. In both paradigms the facial features were presented in a random temporal sequence in order to minimise preferential scanning strategies. The two separate paradigms reflected the feature hierarchy most commonly found in the literature, ie the outline and eyes are more salient than the nose and mouth in terms of both speed of processing and error rate. In a third study the feature substitution paradigm was used to investigate the effects of feature saliency on the perception of emotional faces. The results suggest a change in the eyes/mouth hierarchy so that the mouth becomes the most salient feature in the surprised, happy, and sad target faces. This reverse in hierarchy, however, was not evident with the angry target face. These results are discussed in terms of changes in the focus of 'attention' and/or changes in 'processing efficiency'.

Adult↗
PubMed1990

Assessing the validity of NART-estimated premorbid IQs in the individual case.

The National Adult Reading Test (NART: Nelson, 1982) has become the standard means of estimating premorbid intelligence. The danger in using the NART for this purpose is that it yields an invalid estimate if a client's performance on the test has suffered impairment. In the present study a sample of 659 healthy subjects was used to build a regression equation for the prediction of NART scores from demographic variables (i.e. years of education, social class, age and sex). The multiple correlation between these demographic variables and the NART was .70 (p less than .0001). Comparing a client's obtained and predicted NART score will permit the clinician to assess objectively whether NART performance is impaired, and thus whether or not the NART will provide a valid estimate of premorbid intelligence.

Adolescent↗
PubMed1990

Multimodal imaging in Alzheimer's disease. The relationship between MRI, SPECT, cognitive and pathological changes.

Patients with a clinical diagnosis of Alzheimer's disease were studied using MRI, SPECT, and psychometric tests. Significant correlations between focal perfusion deficits and focal cognitive deficits were found. Significant correlations between regional relaxation time of white matter and psychometric tests of diffuse and focal categories were also found. Pathological examination confirmed Alzheimer's disease as the only diagnosis.

Aged↗
PubMed1989

Magnetic resonance imaging in Alzheimer's disease, multi-infarct dementia, alcoholic dementia and Korsakoff's psychosis.

Regional spin lattice relaxation times (T1) measured during nuclear magnetic resonance imaging of the brain were compared in patients with Alzheimer's disease, multi-infarct dementia, alcoholic dementia, Korsakoff's psychosis and control subjects. Regional differences were found between all patient groups compared with controls and within patient groups, with the exception of the comparison between Korsakoff's psychosis and alcoholic dementia. Correlations between regional T1 change and cognitive test scores were also found, with particular emphasis between visuospatial deficits and parietal T1. The possible role of T1 measures in the pathophysiology of these disorders is discussed.

Aged↗
PubMed1989

Estimating premorbid IQ from demographic variables: regression equations derived from a UK sample.

The purpose of the study reported here was to build regression equations for the estimation of premorbid IQ from demographic variables in a UK population. Subjects (n=151) free of neurological, psychiatric or sensory disability, were administered the Wechsler Adult Intelligence Scale (WAIS) and had their demographic details recorded (age, sex, occupation and education). WAIS Full Scale (FSIQ), Verbal (VIQ), and Performance IQ (PIQ) were regressed on the demographic variables. The regression equations generated by this procedure predicted 50, 50, and 30 percent of the variance in FSIQ, VIQ, and PIQ respectively. These equations should provide a convenient and useful supplement to psychometric estimates of premorbid IQ. Unlike psychometric estimates, demographic estimates are entirely independent of a patient's current cognitive status.

Adolescent↗
PubMed1988

On a changing perspective illusion within Vermeer's The Music Lesson.

The effect of line of sight on the perception of spatial configuration has been investigated in a well-known painting (The Music Lesson by Vermeer) and in two control patterns. In experiment 1, subjects indicated the perceived inclination of two major contours which defined the sidewall-floor and backwall-floor joints in (i) a projected image of the painting, (ii) a three-line representation of the major spatial elements of the painting, and (iii) a three-dimensional wire model of these same contours, when standing in each of eighteen positions on a line running parallel to the surface of the screen. Results indicated a significant change in the perception of the sidewall-floor, but not of the backwall-floor contour, as viewing angle changed, in both the painting and the three-line representation. However, the angular setting in the latter case was significantly less than when the painting was used, ie subjects underestimated the depicted inclination. Settings for the wire model did not deviate with viewing angle and reflected geometrically correct adjustments. In experiment 2, the results of experiment 1 were confirmed using enantiomorphs. These findings are discussed in the light of other view-dependent illusions in paintings.

Adult↗
PubMed1988

Visual parsing and priority effects in temporal order judgements of line drawn patterns.

Five experiments are reported in which the perception of the order of the components of line drawn patterns presented in rapid temporal sequence on a visual display unit was investigated. In experiments 1 and 2, respectively, a schematic face and an asymmetrical geometric design, and a realistic face and a symmetrical geometric design were each divided into four fragments consisting of outline and three internal features. These fragments were presented to observers in sequences in which the position of the outline in the sequence was systematically varied. Observers reported the perceived order of the fragments. If the order was misperceived the interfragment interval was increased until the sequence was correctly perceived. Analysis of the pattern of perceptual errors and the interfragment presentation interval at which the sequence was correctly perceived indicated that observers tended to perceive the sequence correctly when the outline was presented in first or last position, but had difficulty in doing this when it occupied an intermediate position. This effect was significantly stronger with facial than with geometric patterns. Furthermore, in the case of two face patterns, errors were of a form where observers reported the outline presented in positions two or three as occupying positions one or four respectively. In experiment 3 an identical procedure was used to compare the perception of temporally fragmented normal and inverted faces. The outline position effect was equally strong in both cases. In experiment 4 the relative strength of the tendency to move the outline towards first or final position was assessed by dividing each of two patterns, a face and a house, into three fragments consisting of outline and two groups of internal features. Order perception was significantly better with outline in first or third position, but where it was presented in the intermediate position it was reported as being presented in first position. In experiment 5 the general pattern of results obtained in experiments 1, 2, and 3 was verified with the use of a methodology in which pattern fragment sequences and interfragment intervals were both randomised from trial to trial and the observer's task was to specify the position of the outline in the sequence. Four patterns--a normal face, a face with inverted internal features (INF face), a face outline with irrelevant internal features (IRF face), and a geometric design--were each divided into four fragments consisting of outline and three internal features.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗