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Biomedical subjects

G Novak

Publications and source records attributed to G Novak.

15 recordsLinked to original sources
PubMed1992

Mismatch detection and the latency of temporal judgements.

Event-related potentials were recorded in two auditory tasks involving the discrimination of pitch or duration of binaurally presented tones. Frequently-presented nontarget tones, when compared to the same tones in a simple reaction time task, elicited two negative peaks, NA1 and NA2, followed by a positive peak, nontarget positivity. Infrequently-presented target tones, when compared to the nontargets, elicited mismatch negativity (MMN), followed by N2 and P3b. The peak latencies of NA1 and NA2 did not differ between the pitch and duration tasks, but the duration of NA1 and the peak latencies of mismatch negativity, N2, and P3b, as well as reaction time, increased in parallel for the duration task. It is proposed that the NA1-nontarget positivity sequence reflects the initiation, maintenance, and termination of an attention-modulated process, which is required for the performance of an auditory discrimination task, and that the MMN-N2-P3b sequence reflects a process elicited by infrequently-presented targets, which is the main determinant of reaction time under these testing conditions.

Adult↗
PubMed1992

The chronometry of attention-modulated processing and automatic mismatch detection.

Event-related potentials were recorded from normal subjects in an auditory selective attention task. Targets were rare longer (170-ms) tones of a designated pitch, embedded in a sequence of 100-ms standard tones. The effects of attention-modulated processing were evident in the event-related potentials elicited by the standards. Those to relevant standards were similar for easy (1000 Hz vs. 2000 Hz) and hard (1000 Hz vs. 1030 Hz) pitch separations, and were more negative frontocentrally than those to irrelevant standards. Difference waveforms (attended minus unattended standards) revealed Nd, a negative deflection that was earlier in latency for the easy task (onset, 120 ms; peak, 250 ms) than for the hard task (onset, 250 ms; peak, 350 ms). The speed of detection of the deviant longer tones was insensitive to the attention-modulated processes indexed by Nd. Median reaction time did not differ between tasks, although there were more misses and false alarms in the hard task (and nearly all of the latter were to the irrelevant longer tones). Neither direction of attention nor task difficulty affected the latency of mismatch negativity, N2, or P3 (as identified in difference waveforms: attended or unattended longer tones minus their respective standards). The data suggest that performance was guided by two independent but converging processes, automatic mismatch detection of the longer tone and attention-modulated processing of pitch, followed by selection of response.

Adult↗
PubMed1979

Plasmacytoma of the stomach.

A case of gastric plasmacytoma is presented. A detailed study including a selective angiogram described this unusual gastric neoplasm. Pathological examination by both light and electron microscopy confirmed the diagnosis of primary gastric plasmacytoma. The diagnosis and treatment of primary gastric plasmacytoma is discussed and pertinent literature is reviewed.

Aged↗
PubMed1978

Morphologic sequelae to contrast medium deposits in the kidney. An experimental investigation in the rabbit.

Various doses of Pantopaque and Vascoray were injected percutaneously into the kidneys in 17 rabbits. Histologic examination of the kidneys at different time intervals following the injection demonstrated only slight injury to the renal parenchyma which could be related to the contrast media. Therefore, it seems reasonable to assume that the risk of causing renal damage by using Pantopaque in connection with renal cyst puncture is small.

Animals↗
PubMed1977

The production of cerebrospinal fluid in experimental communicating hydrocephalus.

Utilizing an atraumatic model to produce chronic hydrocephalus, CSF production was measured during and after development of communicatin hydrocephalus. CSF volume production was significantly lower in animals with increased pressure. Animals with chronic hydrocephalus and normal pressures had abnormal CSF production. Diminished CSF production appears to offer a potential compensatory mechanism when CSF absorption is altered.

Animals↗
PubMed1977

Evaluation of cerebrospinal fluid production in the development of communicating hydrocephalus.

Diminished absorption of cerebrospinal fluid (CSF) is the most common cause of communicating hydrocephalus. Soon after the absorptive capacity is decreased, the CSF pressure increases, producing ventricular enlargement if the process is not halted. CSF production was measured by ventriculo-cisternal perfusion during and after the production of communicating hydrocephalus, using an atraumatic animal model. Animals with chronic hydrocephalus and normal pressure had normal CSF production. CSF production tended to be lower in animals with increased pressure. When CSF absorption is compromised, decreased CSF production does not appear to be a significant compensatory mechanism.

Acute Disease↗
PubMed1976

The use of diagnostic ultrasound in evaluation of the abdomen in primates with emphasis on the rhesus monkey (Macaca mulatta).

To characterize the sonographic appearance of the abdominal organs in primates, a program of routine imaging and diagnostic evaluation was undertaken. Compound B-mode methodology with bistable and grey scale machines was employed utilizing a 2.25- to 3.5-MHZ transducer focused at 7 cm. Visualization of the liver, gallbladder, spleen, kidney and of intraabdominal pathology are described. The stage, position, and condition of a pregnancy can be determined by this methodology.

Abdomen↗
PubMedDate not supplied

Valproic acid in the treatment of Sydenham chorea.

Severe cases of Sydenham chorea are still difficult to manage because optimal therapy has not been found. In this report severe chorea responded to valproic acid therapy after trials with diazepam and haloperidol had failed. The literature is reviewed and the possible mechanism of action of valproate in this movement disorder is discussed. Valproic acid is proposed as an effective treatment for severe cases of Sydenham chorea.

Child↗