Biomedical subjects

V T Nasman

Publications and source records attributed to V T Nasman.

5 recordsLinked to original sources

PubMed1992

Effect of task decision on P300.

Previous studies have shown that the structure of an experimental task may modulate P300 (P3) responsiveness to task-related test stimuli. In this study, four tasks were compared to study possible effects of decision type on P3s to rare and frequent visual word stimuli. One or three oddballs were designated in two separate experiments. Subjects in each experiment viewed randomized and repeated presentations of nine 5- to 8-letter words, and performed each of four target detection and choice discrimination tasks: (1) silent counting of oddball(s), (2) button-press to oddball(s), (3) choice response ('yes' or 'no') to oddball(s) and frequents, and (4) choice button-press to oddball(s) and frequents. Although oddball stimuli elicited characteristic 'target' P3s over the parietal scalp, there was no significant effect of task type on the oddball-evoked P3. Frequents tended to elicit larger P3s in the choice discrimination tasks (yes/no, go/go) than in target-detection tasks (counting, go/no-go), indicating a selective effect of decision type on P3s to frequent-category events.

Adolescent↗

PubMed1992

Taking attention to task: P300, task response probability, and within-category deviation detection.

Previously, we reported enhanced P3 amplitudes to between-category deviations among high and low probability events. Here, we tested the effects of a within-category difference. Subjects performed a go/no-go button press task as they viewed repeated, randomly-ordered presentations of nine double-digit numbers. Eight numbers fell within a prescribed range (42-49, standards); prior to testing, subjects selected one standard number for later recall. A ninth, out-of-range (91, deviant) number was also included. Subjects were tested under two conditions, in which they responded either to one (low response probability) or to seven (high response probability) standard nonselected numbers, designated as targets. Relatively larger P3s were consistently apparent only when the deviant nontarget was associated with a low probability response to a nontarget. There was a selective effect of nontarget response probability on P3 amplitude to the deviant nontarget. Our results indicate that within-category deviation detection is facilitated by "controlled" attention to the structure of the stimulus field.

Adolescent↗

PubMed1990

Parietal P3 response as an indicator of stimulus categorization: increased P3 amplitude to categorically deviant target and nontarget stimuli.

Two experiments were performed in which we compared the effects of selected non-deviant versus categorically deviant stimuli on parietal P3 under a variety of conditions in which one, both, or neither stimulus was a target of an experimental task. Subjects were repeatedly presented with series of 8 numeric stimuli and 1 alphabetic (Deviant) stimulus. P3 amplitudes to target and nontarget Deviant stimuli were consistently and significantly larger than to other, non-deviant targets and nontargets, respectively. Nontarget Deviant stimuli evoked P3 amplitudes comparable to those evoked by low-probability non-deviant targets. The observed differences indicate that P3 amplitude is a sensitive indicator of perceived category differences, and that the effect of category deviance on parietal P3 amplitude is independent of task response classification (target or nontarget) and of response probability.

Adolescent↗

PubMed1988

A modified, event-related potential-based guilty knowledge test.

Subjects chose and pretended to steal one object from a box of nine. They then watched a visual display of verbal representations of objects including their chosen object or one of eight novel objects on each trial. They were told to count one of the novel objects and that although they were welcome to try to beat our test, they would be unable to avoid noticing the chosen object. P3 responses were obtained only to counted and to chosen objects in 7 of 10 subjects not eliminated for artifact or noncooperation.

Guilt↗

PubMed1987

Late vertex positivity in event-related potentials as a guilty knowledge indicator: a new method of life detection.

Subjects were allowed to choose an item to keep from nine items in a box. They then were shown one of nine words randomly selected on a display screen. One of these words described the chosen item, the others described novel items. The subjects were told to try not to react emotionally to any of the words, but to try to defeat this test of deception. It was found that large positive waves with latencies between 400 and 700 ms poststimulus were present in the ERPS to the chosen but not to the novel words.

Adolescent↗