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Biomedical subjects

H A Allen

Publications and source records attributed to H A Allen.

At least 19 recordsLinked to original sources
PubMed2000

Slow discrimination of contrast-defined expansion patterns.

We compared observers' performance in the same complex motion discrimination task using stimuli defined by luminance or by contrast. They were asked to discriminate between a centred expansion pattern, constructed from four patches of outwards motion, and a distorted expansion pattern, constructed with one patch containing inwards motion and three patches containing outwards motion. We measured performance versus duration and found that for luminance-defined patterns, observers were able to discriminate correctly between these patterns in 75% of trials when the stimulus duration was 200 ms. For contrast-defined patterns, observers required over 2 s to reach this level of performance. Observers did not require such long durations to discriminate correctly between the contrast-defined expansion patterns when the patterns contained fewer patches or when the distorted patterns contained more patches of inwards motion. This suggests that observers performed the task by searching for a patch that contained a pattern moving inwards. There was no such effect on performance with the luminance-defined patterns. These results also suggest that contrast-defined patterns are processed too slowly to provide an input to specialised optic flow detectors that guide navigation in real time. Further, the differences in performance may be due to processing delays from sequential processing of the contrast-defined local motion signals.

Contrast Sensitivity↗
PubMed1993

Negative features, retrieval processes and verbal fluency in schizophrenia.

Twenty chronic schizophrenic patients, ten matched normal controls and nine depressed controls performed categorical verbal fluency tasks for three minutes each on five separate occasions. On each occasion the schizophrenic patients generated significantly fewer words than the controls. Comparison of the different occasions showed that the schizophrenic patients had as many words available in their inner lexicons but were inefficient in retrieving them. The schizophrenic patients also generated fewer clusters of related words and more words outside the specified category. Reduced ability to generate words while the lexicon remained intact was more marked in patients with negative features. Patients with incoherence, in contrast, were more likely to produce inappropriate words. We propose that both poverty of speech and incoherence of speech reflect problems in the retrieval of words from the lexicon. To cope with these problems patients with poverty of speech terminate their search prematurely while the patients with incoherence commit errors in selecting words for output.

Adolescent↗
PubMed1989

CT demonstration of the appendix in asymptomatic adults.

We prospectively examined 103 consecutive adults (67 women, 36 men; mean age: 58.7 years) referred for abdominal and pelvic computed tomography (CT) in whom there was no history of right lower quadrant symptoms or appendectomy. Contiguous 5-mm CT images through the pericecal region were obtained in each subject, once routine scanning was completed. Three radiologists reviewed all CT images and reached a consensus on appendiceal visualization and the quantity of intraperitoneal fat. Statistical methods were applied to the collected data to seek significant associations between a visualized appendix and the following factors: patient age, sex, intraperitoneal fat grade, and the presence of oral contrast in the cecal lumen. The appendix was definitely visualized in only 45 of the 103 patients (43.7%). Analysis of variance revealed no statistically significant correlation between a CT-demonstrated appendix and the four variables examined. The clinical implications of these findings are discussed.

Adolescent↗
PubMed1989

Parasternal sonography of the internal mammary vessels: technique, normal anatomy, and lymphadenopathy.

Metastasis to the internal mammary lymph nodes adversely affects the disease-free interval and long-term survival in women with breast carcinoma. Since staging of disease in this lymphatic chain is rarely performed at the time of definitive surgical treatment, noninvasive methods have been advocated. The authors present their preliminary experience with a sonographic technique for evaluating the internal mammary lymph nodes, artery, and vein. Longitudinal and transverse images of the first through fourth parasternal rib interspaces were acquired with a 5.0- or 7.5-MHz linear-array real-time system. The method was evaluated prospectively in 36 control subjects and in seven patients (six with metastatic breast cancer and one with lymphocytic lymphoma) who had enlarged internal mammary lymph nodes at thoracic computed tomography (CT). The longitudinal scans routinely demonstrated the internal mammary vessels in the upper interspaces. Lymphatic structures were not identified in the control group. In contrast, sonographic findings corresponding to the CT findings of lymphadenopathy were present in all seven patients. The authors believe that parasternal sonography is a promising technique that merits further study.

Adult↗
PubMed1988

Bilateral ectopic pheochromocytomas: computed tomographic and sonographic correlation.

We describe a case of clinically unsuspected bilateral ectopic pheochromocytomas in a young woman. The bilateral retroperitoneal masses were located in the lower sympathetic ganglia at the level of the organ of Zuckerlandl. Computed tomography (CT) accurately identified the location and vascular characteristics of these neoplasms and provided access for percutaneous biopsy. Sonographic correlation is also presented.

Adult↗
PubMed1988

Rock-climbing injuries in Yosemite National Park.

This study was presented in part at the annual meeting of the Wilderness Medical Society at Aspen, Colorado, in August 1986 and at "Mountain Medicine 1987," Leavenworth, Washington, in November 1987. We questioned 220 injured rock climbers or their partners seen consecutively at the Yosemite (California) Medical Clinic over 3 (1/2) years regarding details of their accidents. Injury type and location were extracted from medical records and severity quantified. The National Park Service rescued 27% of the climbers. Injured climbers were characteristically male (88%) and experienced (mean 5.9 years) and typically fell while leading climbs (66%). Among 451 injuries, 50% were to the skin or subcutaneous tissues, while 28% involved the lower extremity and were predominantly fractures. In terms of each climber's most severe injury (n = 220), 45% involved the lower extremities (30% from the ankle alone). Head injury or hypothermia caused 12 of 13 fatalities, showing the lowest case-fatality rate reported to date among injured climbers (6%). Rescue personnel successfully managed airways in victims of head injuries, anticipated and treated complications of hypothermia, and stabilized fractures. Victims requiring immediate extensive surgical intervention or blood transfusion usually died before rescue could be effected.

Accidental Falls↗
PubMed1987

Actinomycosis: CT findings in six patients.

Actinomycosis is an uncommon disease with clinical and radiographic findings that overlap those of other inflammatory and neoplastic conditions. A retrospective review of CT scans in six proved cases revealed a spectrum of findings, including soft-tissue mass with various degrees of infiltration and abscess formation. Administration of IV contrast material was helpful in defining the loculations of the abscess in two cases. Areas of involvement included the neck (two cases), liver (one case), abdominal wall (one case), thorax (one case) and kidney and retroperitoneum (one case). CT findings of a soft-tissue mass in the neck, lungs, or abdomen, with or without a draining sinus or fistula, raise the possibility of actinomycosis in patients with clinical findings that suggest a subacute or chronic inflammatory process.

Actinomycosis↗
PubMed1985

Positive symptoms and the organization within and between ideas in schizophrenic speech.

The study examined the performance of positive symptom schizophrenics vis à vis that of demographically well-matched negative symptom schizophrenics and normals in organizing words into ideas and ideas into integrated spoken discourse. This involved applying a series of analyses to speech produced when describing pictures in an unconstrained way. The results showed that, for the most part, positive symptom schizophrenics organized their speech, both within and between ideas, as well as negative symptom schizophrenics and normals. The results did, however, show an increased tendency by the positive speech disordered schizophrenics to omit referents for noun phrases requiring referents. This constitutes a specific failure to connect ideas and does, at least in part, explain what makes positive speech disorder (incoherence of speech) unintelligible. However, taken altogether, the results do not support the extant view that positive symptom schizophrenics suffer from a general loss of control in producing speech.

Adult↗
PubMed1985

Can all schizophrenic speech be discriminated from normal speech?

The study addressed whether the speech of non-speech disordered as well as speech disordered schizophrenics is discriminable from normal speech. An analysis, using a clinician's acumen to detect, not as is usually the case to specify, showed that schizophrenic speech (including that of non-speech disordered schizophrenics) can be accurately discriminated. This suggests that the speech of all schizophrenics does indeed differ from that of normals, but in as yet unspecified ways.

Humans↗
PubMed1984

Vascular studies in the preoperative evaluation of pituitary adenomas before transsphenoidal surgery.

The transsphenoidal approach is being increasingly utilized in the surgical treatment of pituitary microadenoma. Even with high-resolution and dynamic computed tomography (CT) scanning, subtle vascular anatomic variants and other vascular anomalies involving the parasellar carotid arteries cannot always be clearly defined. Five cases are described in which evaluation by digital intravenous subtraction angiography or standard carotid arteriography provided useful preoperative information before transsphenoidal surgery. The implications of these findings are discussed.

Adenoma↗
PubMed1984

Left ventricular outflow obstruction and necrotizing enterocolitis.

Two neonates had unusually rapid development of necrotizing enterocolitis within 24 hours of birth. Both patients had decreased systemic perfusion secondary to aortic atresia. Onset of either clinical or radiographic manifestations of necrotizing enterocolitis in the first day of life should alert one to the possible presence of severe left ventricular outflow obstruction.

Aorta↗
PubMed1984

Positive and negative symptoms and the thematic organisation of schizophrenic speech.

This study questions the prevailing view that schizophrenic delusions, hallucinations and incoherence of speech (positive symptoms) reflect loss of cognitive control and that flattening of affect and poverty of speech (negative symptoms) reflect restriction of cognitive processing. The prevailing view was examined by analysing the thematic organisation of speech produced by 18 patients describing pictures. Results showed that (a) positive and negative symptom schizophrenics did not differ in the control and restriction of thematic speech organisation; (b) speech disordered schizophrenics, positive as well as negative, showed cognitive restriction, by producing fewer inferential ideas than non-speech disordered schizophrenics. The wider implications of these results are discussed, particularly the implications of (b) for the notion of concreteness in schizophrenia.

Adult↗
PubMed1984

Sonography of emphysematous pyelonephritis.

Emphysematous pyelonephritis is a rare gas-producing bacterial infection of the renal parenchyma seen primarily in patients with diabetes mellitus. Sonographic findings in four patients with this disease are described. Sonographic features consist of multiple high-amplitude echoes within the renal parenchyma, renal sinus, and/or perirenal space accompanied by acoustic shadowing. Computed tomography confirmed bilateral involvement in one case. Plain abdominal radiographs demonstrated abnormal extraluminal gas in three of four cases. The role of sonography in diagnosis is discussed.

Aged↗
PubMed1983

The skin conductance orienting response as an index of attention.

In Experiment I 41 subjects performed one of three tasks while also hearing irrelevant tones tones. The three tasks were forewarned reaction time, vigilance and mental arithmetic and each was divided into discrete trials. The irrelevant tones either occurred during task performance (i.e., within a trial) or outside task performance (i.e., between trials). There was no difference in skin conductance OR magnitude to tones across the three tasks. Heart rate changes in contrast showed clear differences between tasks with a marked deceleration occurring during forewarned reaction time and a marked acceleration occurring during mental arithmetic. Skin conductance OR magnitude was significantly greater to tones occurring during task performance than to tones occurring outside task performance. This was interpreted as reflecting changes in the level of attention (higher during task performance) rather than direction of attention (away from tones during task performance). In Experiment II 39 subjects heard a series of irrelevant tones either while performing a forewarned reaction time task as in Experiment I or while performing no concomitant task. Rate of habituation was significantly faster for the subjects performing the concomitant task. This was interpreted as reflecting direction of attention which should be away from the tones when the subject was performing a concomitant task. Thus while rate of habituation to a class of stimuli may reflect direction of attention, short-term changes in OR amplitude probably reflect level of attention.

Acoustic Stimulation↗