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Biomedical subjects

G W Stuart

Publications and source records attributed to G W Stuart.

At least 55 records · Page 3Linked to original sources
PubMed1993

Perceptual learning in seeing form from motion.

Some perceptual tasks, such as global stereopsis, have been shown to improve with practice. Paradigms that involve such 'perceptual learning' have been exploited to learn more about the nature and sites of these perceptual tasks in the brain and about plasticity in the adult central nervous system. We found that seeing structure from global motion in some kinematograms composed of tilted line elements required a period of learning. However, such learning was specific neither to the orientation of the line elements nor to the direction of global motion, even though detection of these line elements and the direction of motion was necessary for seeing the global structure in these kinematograms. Our results suggest that the neural site of deriving form from motion is beyond the level of individual motion and pattern detectors. In both its nature and locus along the hierarchy of the visual system, this learning is quite different from other types of perceptual learning reported so far.

Adult↗
PubMed1993

Reconceptualizing the psychiatric head nurse role.

The increasing complexity and specialization of psychiatric services mandate changes in the management of people and the delivery of health care. These changes have occurred simultaneous with significant progress in the discipline of psychiatric nursing and its evolvement into expanding areas of clinical expertise, higher levels of education, and growing sophistication in research. Such significant changes require that the role of the psychiatric head nurse be reexamined and reformulated to facilitate its alignment with the current realities of the health care environment. Important considerations in redesigning the psychiatric head nurse role are identified, and an actualization of the new role in one inpatient setting is described.

Education, Nursing, Continuing↗
PubMed1993

Positive and negative symptoms in the psychoses. Re-analysis of published SAPS and SANS global ratings.

The validity of the simple dichotomy between positive and negative symptoms was examined by reanalysing the results of published studies using global ratings from Andreasen's SAPS and SANS. Global ratings from our own sample of 114 diagnostically heterogenous psychotic patients were also analysed. In none of the studies was a simple positive-negative dichotomy an adequate representation of symptom structure. The most commonly occurring structure consisted of three independent groups: Hallucinations/Delusions, Positive Thought Disorder and Negative Symptoms. These findings applied to both manic and schizophrenic groups of patients. An important implication of these results for future studies is that combining positive symptoms into a single scale is inappropriate because possibly differential relationships between Hallucinations/Delusions and Thought Disorder and a variety of external measures may be obscured by such a means of data reduction.

Affective Symptoms↗
PubMed1993

Preattentive processing of object size: implications for theories of size perception.

Information about the visual angle size of objects is important for maintaining object constancy with variations in viewing distance. Although human observers are quite accurate at judging spatial separations (or cross-sectional size), they are prone to error when there are other spans nearby, as in classical illusions such as the Müller-Lyer illusion. It is possible to reconcile these aspects of size perception by assuming that the size domain is sampled sparsely. It was shown by means of a visual search procedure that the size of objects is processed preattentively and in parallel across the visual field. It was demonstrated that an object's size, rather than its boundary curvature or spatial-frequency content, provides the basis for parallel visual search. It was also shown that texture borders could be substituted for luminance borders, indicating that object boundaries at the relevant spatial scale provide the input to size perception. Parallel processing imposes a severe computational constraint which provides support for the assumption of sparse sampling. An economical model based on several broadly tuned layers of size detectors is proposed to account for the parallel extraction of size, the Weberian behaviour of size discrimination, and the occurrence of strong interference effects in the size domain.

Attention↗
PubMed1993

The factor structure of the Turkish version of the General Health Questionnaire.

The 60-item General Health Questionnaire (GHQ) was translated into Turkish and administered to a community sample of 437 Turkish-speaking immigrants resident in Melbourne, Australia. The factor structures of the 60-item and 28-item versions of the GHQ were examined to determine the cross-cultural validity of the four subscales of the 28-item GHQ "anxiety/insomnia", "social dysfunction", "severe depression" and "somatic complaints". Four-factor principal components analyses yielded factors which corresponded to similar underlying traits, but the pattern of symptom loadings differed in several ways. Insomnia was less closely associated with anxiety, and general illness ratings such as "not feeling perfectly well" were not uniquely associated with somatic symptoms. The "anxiety/insomnia" and "severe depression" factors overlapped, with many symptoms partially correlated with both factors. These factors appeared to be due to variations in the frequency of occurrence of these symptoms rather than a qualitative distinction between anxiety and depression.

Acculturation↗
PubMed1993

Preliminary report: placebo-controlled, double-blind study of the clinical and metabolic effects of desipramine in panic disorder.

Fifty-six males and females with panic disorder with or without agoraphobia participated in a 12-week, placebo-controlled treatment study of the efficacy of desipramine (DMI). Twenty-six of 28 patients receiving DMI completed the study; 17 of 28 placebo (PBO) recipients completed 12 weeks. Patients receiving DMI responded significantly better than did PBO recipients as measured by Hamilton Anxiety Scale (HAM-A) and global phobia ratings, with a trend toward greater global improvement, but no between-group differences on panic attack frequency were discerned. By Week 12, 22 of 26 (85%) DMI patients were panic-free; 13 of 17 (76%) PBO patients were panic-free. Resting metabolic rate (RMR) was tested on a subset of the patients. Patients receiving DMI showed no effects on RMR or thyroid indices but lost a significant amount of weight; the PBO recipients exhibited no weight loss or RMR effects. In this study, the high PBO response rate obscured treatment group differences on some measures. This study underscores the need for placebo comparisons in treatment studies. In summary, DMI appears to be an effective treatment for panic disorder. DMI appears to have little effect on RMR; a slight but significant weight loss was observed in the DMI but not PBO group.

Adolescent↗
PubMed1992

Positive and negative symptoms in the psychoses: multidimensional scaling of SAPS and SANS items.

Recently, the validity of the simple dichotomy between positive and negative symptoms in psychosis has been questioned. A newly admitted group of 114 DSM-III patients with psychotic disorder were assessed using Andreason's positive and negative symptoms scales. Multidimensional scaling, augmented by cluster analysis, was applied to the full item set of these scales and showed clearly that there are three major, independent groups of symptoms: Hallucinations/Delusions, Positive Thought Disorder and Negative Symptoms. Within the Hallucinations/Delusions and Negative Symptoms groups there was some additional structure which does not conform to the SAPS and SANS sub-scales. In particular there was considerable heterogeneity within the Hallucinations/Delusions group, and delusions of persecution may represent a fourth independent dimension of psychopathology which is under-represented in these scales.

Adult↗
PubMed1992

Cooperative representation of visual borders.

Recently it has been reported that the visual cortical cells which are engaged in cooperative coding of global stimulus features, display synchrony in their firing rates when both are stimulated. Alternative models identify global stimulus features with the course spatial scales of the image. Versions of the Munsterberg or Café Wall illusions which differ in their low spatial frequency content were used to show that in all cases it was the high spatial frequencies in the image which determined the strength and direction of these illusions. Since cells responsive to high spatial frequencies have small receptive fields, cooperative coding must be involved in the representation of long borders in the image.

Attention↗
PubMed1992

Colour inputs to random-dot stereopsis.

Recently it has been claimed by Livingstone and Hubel that, of three anatomically and functionally distinct visual channels (the magnocellular, parvocellular interblob, and blob channels), only the magnocellular channel is involved in the processing of stereoscopic depth. Since the magnocellular system shows little overt colour opponency, the reported loss of the ability to resolve random-dot stereograms defined only by colour contrast seems consistent with this view. However, Julesz observed that reversed-contrast stereograms could be fused if correlated colour information was added. In the present study, 'noise' (non-corresponding) pixels were injected into random-dot stereograms in order to increase fusion time. All six subjects tested were able to achieve stereopsis in less than three minutes when there was only correspondence in colour and not in luminance, and three when luminance contrast was completely reversed. This ability depends on information about the direction of colour contrast, not just the presence of chromatic borders. When luminance and chromatic contrast are defined in terms of signal-to-noise ratios at the photoreceptor mosaic, chromatic information plays at least as important a role in stereopsis as does luminance information, suggesting that the magnocellular channel is not uniquely involved.

Color Perception↗
PubMed1992

Visual processing deficits in dyslexia: receptors or neural mechanisms?

In 1989 and 1990 Grosser and Spafford attributed abnormalities in the peripheral vision of dyslexic subjects to an anomalous distribution of rods and cones. We argue that at the light levels used in these experiments cone responses should dominate both central and peripheral vision. A more likely explanation of their findings is that there is a postreceptoral deficit in the transient visual channel. This hypothesis is supported by independent anatomical, physiological, and psychophysical evidence.

Attention↗
PubMed1992

The effects of pregnancy on preexisting panic disorder.

BACKGROUND: Limited evidence suggests that pregnancy may be associated with a reduction of panic and related symptoms. The authors investigate reported changes in panic symptoms during pregnancy. METHOD: Questionnaires asking about changes in panic and phobic avoidance symptoms during pregnancy were mailed to 129 women who had previously participated in our Anxiety Disorders Program over a 5-year period; all had diagnoses of panic disorder by DSM-III-R criteria. Reported here are responses from 22 of the women who experienced pregnancy after the onset of panic disorder. RESULTS: A majority of women (14 of 22) reported a decrease in panic symptoms during pregnancy, but significant variability in this phenomenon occurs between and within individuals. CONCLUSION: A subpopulation of women may experience improvement in panic symptoms during pregnancy, which has implications for management of these patients. Further research is needed to verify the existence of such a subpopulation and to determine an etiology.

Agoraphobia↗
PubMed1991

Concordance with recommendations in a consultation-liaison psychiatry service.

We studied the concordance of physicians with the recommendations of psychiatric consultants in a sample of 270 consultations in a 400-bed general hospital. Of the patients about whom a consultation was sought, 37% had a past psychiatric history, and 67% were on psychotropic drugs. Twelve percent had Organic Mental Disorder, 35% Affective Disorder, and for 24% no DSM-III diagnosis could be made. The psychiatrist made psychotropic drug recommendations in 62%, and the physicians' concordance with this recommendation was 86%. The physician's discharge summary included a diagnosis which concorded with the psychiatrist's diagnosis in 53% of files. The psychiatrist recommended further investigations in only 5.2% of files.

Adolescent↗
PubMed1991

Comparison of participants and nonparticipants in a neuroendocrine investigation of psychosis.

Of all neuroleptic-naive, acutely psychotic subjects admitted to hospital over a 2-year period (n = 62), 27 participated in a neuroendocrine study and 35 did not participate (51% refused consent, 19% were incapable of consent and 31% started neuroleptics immediately). However, all nonparticipants agreed to psychopathological evaluation, thus allowing comparison between participants and nonparticipants. The 2 groups were similar in most respects, except that more nonparticipants were hostile. Among subjects with schizophrenia, 47% of nonparticipants had the paranoid subtype vs 8% of participants. There was also a trend towards longer illness duration in nonparticipants. These results underline the need for neurobiological studies of psychosis to consider sample bias as a confounding variable.

Adult↗
PubMed1991

The prevalence of psychiatric morbidity in general hospital inpatients.

The aim of this study was to examine the prevalence of psychiatric morbidity in a sample of medical and surgical inpatients in an Australian general hospital. Using the 60-item General Health Questionnaire, the estimated prevalence was 30% (previous studies have yielded estimates generally between 20 and 50%). The prevalence of morbidity was significantly higher in medical (45%) than in surgical (23%) inpatients. Twelve percent of patients (20% of medical patients and 8% of surgical patients) satisfied DSM-III criteria for a current Major Depressive Episode. Anxiety scores on the State-Trait Anxiety Inventory were higher than those reported in general population samples. There were no significant differences between males and females on any scores. The problems associated with the definition and identification of depressive and anxiety syndromes in medical and surgical inpatients are discussed, whilst the importance of this task is emphasized.

Anxiety Disorders↗