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N Graham

Publications and source records attributed to N Graham.

At least 91 records · Page 5Linked to original sources
PubMed1987

Summation of very close spatial frequencies: the importance of spatial probability summation.

In accounting for pattern thresholds it is necessary to consider probability summation (or equivalent nonlinear pooling) not only across detectors selective for different spatial frequencies but also across detectors in different spatial positions. Interestingly, calculation on this basis shows that the amount of summation between components of closely similar spatial frequency in a large grating is primarily determined by the variation in sensitivity of detectors at different spatial locations and is little affected by the spatial-frequency bandwidths of the detectors. To test this conclusion, we have measured the amount of summation between two components with spatial frequencies very close to 6 c/deg in two regions of the visual field: in the fovea (a region where sensitivity is very non-uniform) and in the periphery (where sensitivity is nearly uniform). As predicted, there was less summation between components of very closely similar frequencies in the nearly-uniform peripheral region than in the non-uniform foveal region. Measurements in the fovea of the summation of two components with spatial frequencies very near to either 1.5, 6 or 24 c/deg showed, as expected, that the amount of summation depends upon the ratio of the frequencies rather than their absolute difference, indicating that probability summation takes place over an area related to spatial frequency rather than over a fixed area.

Female↗
PubMed1987

Cognitive impairment, emotional disorder and length of stay of elderly patients in a district general hospital.

All patients over 65 in a district general teaching hospital (n = 204) were screened for cognitive impairment and emotional disorder using the Clifton Assessment Procedures for the Elderly, the Mini-Mental State and the General Health Questionnaire. Patients scoring in the disordered range were psychiatrically assessed. These procedures gave an estimated prevalence of cognitive impairment of 22 per cent in the 164 patients satisfactorily assessed. Forty-three per cent of patients scored beyond the GHQ cut-off, but there was a high false positive rate. Cognitively impaired patients had a significantly longer hospital stay than the unimpaired. The majority (60 per cent) of these patients could not be discharged because of lack of an appropriate place elsewhere. Amongst all elderly patients whose discharge was prevented in this way, the cognitively impaired were markedly over-represented. The data have implications for the efficient use of hospital beds and for the welfare of elderly patients in acute hospitals.

Affective Symptoms↗
PubMed1987

Maternal plasma bicycling PGE2 levels following vaginal administration of prostaglandin E2 pessaries in full term pregnancies.

Plasma levels of bicyclic PGE2 (PGE2M) were measured after administration of a 5mg, PGE2 slow release hydrogel pessary and a 3mg vaginal tablet (Upjohn). Twenty-four women of low parity with favourable induction features were randomised to receive either the hydrogel pessary or the vaginal tablet. A single pessary was administered and amniotomy was performed after 4 hours. Augmentation with oxytocin was carried out after amniotomy if required. Both groups showed a rise in plasma PGE2 levels in keeping with the release profiles of the pessaries. Wide interindividual differences in absorption were found.

Administration, Intravaginal↗
PubMed1985

Cystic fibrosis: ultrasonographic findings in the pancreas and hepatobiliary system correlated with clinical data and pathology.

Abdominal ultrasonography was performed on 35 adult patients with proven cystic fibrosis. Thirty-three patients showed pancreatic abnormalities. The most marked ultrasonographic features were increased parenchymal echogenicity, atrophy, non-visualisation of the duct and cyst formation. There was no correlation between these features and the severity of the pulmonary disease, the age of the patient, weight or glucose intolerance. Abnormalities of the biliary tract were demonstrated in nine (26%) patients and were associated with poor nutritional status. Multivariate analysis revealed a significant association between the following: hepatomegaly, increased liver echogenicity, splenomegaly, biliary disease; secondly, between lung function and serum albumin. Ultrasonography is useful in showing organ morphology but not in assessing disease severity.

Adolescent↗
PubMed1985

Detection and identification of near-threshold visual patterns.

For a number of visual dimensions--spatial frequency, orientation, spatial position, and direction of motion (at velocities higher than 1 or 2 deg/sec)--experimental results at near-threshold contrasts can be explained by assuming that multiple mechanisms selectively sensitive along that dimension exist and have labeled outputs. For the temporal-position dimension, analogous experimental results can be explained by assuming that each mechanism's output at a particular time depends only on the recent past and is labeled. For the eye-of-origin dimension, however, although the evidence suggests selectively sensitive mechanisms (at least at some spatial and temporal frequencies), these mechanisms seem not to have labeled outputs. For the temporal-frequency dimension (at any fixed spatial frequency), evidence suggests that there are not narrowly tuned mechanisms although there may be very broadly tuned ones.

Attention↗
PubMed1985

Simultaneous measurement of spatial-frequency summation and uncertainty effects.

The predictions for summation and uncertainty effects from several multiple-spatial-frequency-channels models were calculated. The models differed in their assumptions about the shape of the channels' underlying probability-density functions and in the decision rule used to combine the channels' outputs. Varying these assumptions resulted in quite different predictions about the magnitudes of these effects. Simultaneous summation and uncertainty experiments measured the detectability of gratings containing one (simple) or two (compound) spatial frequencies. Performance was assessed in two types of blocks of trials: either each stimulus was in a separate block or three stimuli (two simple gratings and their compound) were randomly intermixed in one block. Quantitative comparisons of the models with the data showed that the increasing-variance Gaussian models (in which the decision variable is the sum of the monitored channels' outputs) provided the best overall fit.

Attention↗
PubMed1984

Detection and identification of spatial frequency: models and data.

Detection and identification of up to four simple sinusoidal gratings were studied. The experimental results were quantitatively compared to predictions from several models. The models all assumed probabilistically independent channels sensitive to different ranges of spatial frequency. The models differed in the shapes of their underlying distributions and, for detection, their decision rule. Detection and identification of far-apart spatial frequencies were consistent with these models. Thus, uncertainty effects for both detection and identification (the decrease in performance with an increase in the number of possible spatial frequencies) can be explained without assuming that attention capacity is limited.

Attention↗
PubMed1984

Psychiatric illness in residential homes for the elderly: a survey in one London borough.

The mental state, demographic details, dependency level and presence of problem behaviours have been recorded for 438 (82%) of the residents of the 12 Part III homes, managed by the London Borough of Camden, using standard interview. One third of the residents were suffering from severe dementia, another third from mild to moderate dementia and one third were free of dementia. Of the latter two groups, 38% were depressed. The prevalence rate of dementia increased with the age of the resident and was higher among females. Depression was associated with the presence of visual handicap and incontinence, and was commoner when the resident had been admitted from his own home or belonged to a minority religion. A third of residents needed daily help with dressing and use of the lavatory, one quarter were incontinent each day. Depression and dementia both were associated with increased rates of dependency and of problem behaviours (incontinence, wandering, aggression). This survey has revealed evidence of sufficient psychiatric morbidity in these homes to support a re-appraisal of their current aims, staffing and health-care provision.

Aged↗
PubMed1982

Simultaneous recognition of two spatial-frequency components.

A two-frequency two-response paradigm was employed. The stimulus on any trial was a compound grating containing two sinusoidal components of different spatial frequencies where the contrast in one or both components could be zero. The observer gave two responses each indicating confidence that one of the two components had been presented with contrast greater than zero. If these responses are assumed to be related to outputs of spatial-frequency channels according to specified recognition linking hypotheses, then channel properties such as bandwidth, negative influences, correlation of noise, and additivity can be inferred. Possible modifications of spatial frequency channel models are discussed.

Form Perception↗
PubMed1982

Transient visual obscurations, without papilloedema.

Two cases of frontal, space occupying tumour without papilloedema are reported. Both presented with frequent, stereotyped attacks of visual disturbance with orbital headache, neck pain and unsteadiness of gait. Intermittent occipital lobe ischaemia, related to compression of the posterior cerebral artery against the tentorium by distorted, herniating brain, seems a probable explanation.

Adult↗