Biomedical subjects

D G Humphrey

Publications and source records attributed to D G Humphrey.

6 recordsLinked to original sources

PubMed1999

Error-related processing during a period of extended wakefulness.

The nature of error detection as manifested by the error-related negativity was examined in both a Sternberg memory search task and a visual search task. Both tasks were performed in conditions with consistent or varied stimulus-response mapping and loads of three or six letters. After subjects were trained extensively in all conditions, they performed the tasks throughout the night without sleeping. The data suggest that the effectiveness of error detection decreases over time because of a decrease in the quality of perceptual processing. Error detection also suffers when performance requires more search-related resources. In both cases, the representation of the correct response is compromised. These results indicate that error detection depends on the same perceptual and cognitive processes that are required for correct performance.

Adult↗

PubMed1997

Age differences in visual search for feature, conjunction, and triple-conjunction targets.

The authors examined the ability of younger and older adults to search for targets defined by single features (feature search), conjunctions of 2 features (conjunction search), and conjunctions of 3 features (triple-conjunction search). Feature search was relatively age-invariant, with both older and younger adults displaying shallow search slopes. However, older adults did show reduced search rates for many conjunction targets. Interestingly, both older and younger adults benefited equivalently when an extra feature was available to define the conjunction target. That is, the relative amount of improvement in search performance was similar for younger and older adults when the triple-conjunction search was compared to the conjunction search. These results are discussed in terms of age-related differences in the effectiveness of bottom-up and top-down mechanisms that support visual search.

Adolescent↗

PubMed1994

Toward a psychophysiological assessment of dynamic changes in mental workload.

The main goal of the present study was to examine the feasibility of employing event-related brain potentials to measure dynamic changes in mental workload. Subjects performed two tasks, monitoring and mental arithmetic, both separately and together. Following an analysis of the performance, subjective workload ratings, and average ERP data in the single- and dual-task conditions, two different conditions from each of the tasks were selected for further analysis. A bootstrapping approach was employed to determine the amount of ERP data required to discriminate between these conditions. The results of these analyses indicated that (a) 90% correct discrimination could be achieved with from 1 to 11 s of ERP data, (b) the best ERP measures varied across tasks and subjects, and (c) the inclusion of temporal and spatial aspects of the ERP data improved the ability to discriminate among workload levels. The data is discussed with respect to real-time assessment of mental workload.

Adult↗

PubMed1994

Influence of extended wakefulness on automatic and nonautomatic processing.

We investigated the influence of extended wakefulness on automatic and nonautomatic processes in memory and visual search tasks. Subjects were trained in consistently mapped and variably mapped versions of each task, attaining automatic performance in the consistently mapped versions. We then recorded performance measures and event-related brain potentials for a 14-h period that began during the evening of the last day of training. Overall performance declined with extended wakefulness, but the benefits of consistently mapped training were retained throughout the night. Performance decrements consisted of an increase in nonresponses, increased response latencies, and decreased accuracies. P300 latencies increased, and P300 amplitudes decreased with extended wakefulness. When viewed together, reaction time and event-related brain potentials measures suggest that the locus of extended wakefulness effects was during early perceptual processes.

Adult↗

PubMed1994

Aging and inhibition: beyond a unitary view of inhibitory processing in attention.

The authors examined the question of whether a decrease in the efficiency of inhibitory processing with aging is a general phenomenon. Thirty elderly and 32 young adults performed a series of tasks from which the authors could extract measures of inhibitory function. The tasks and task components included response compatibility, negative priming, stopping, spatial precuing, Wisconsin Card Sorting Test (WCST), and the Cognitive Failures Questionnaire (CFQ). Only limited evidence for age-related differences in inhibitory function was obtained. Old adults had more difficulty than young adults in stopping an overt response and adopting new rules in a categorization task. However, elderly and young adults produced equivalent negative priming effects, response compatibility effects, spatial precuing effects, and self-reported cognitive failures. The findings are discussed in terms of the relationship between aging, inhibitory processes, and neuroanatomical and physiological function.

Adolescent↗

PubMedDate not supplied

Age-related differences in perceptual organization and selective attention: implications for display segmentation and recall performance.

The present research examined age-related differences in the use of structural aspects of the visual environment to facilitate the processing of task-relevant stimuli. More specifically, our study considered age-related differences in the use of color and proximity to facilitate the recall of alphabetic strings. The dependent measure of interest was the difference in percent recalled for items when grouped into the first or second of two groups that comprised the alphabetic string. When differences in visual short-term memory were controlled, old adults demonstrated a greater sensitivity to grouping by proximity and grouping by similarity than did younger adults. This increase in recall as a function of grouping is consistent with Craik's (1986) (In F. Klix & H. Hagendorf [Eds.], Human memory and cognitive capabilities, mechanisms, and performances [pp. 409-422]. North Holland: Elsevier) view that older adults can benefit when environmental support is provided for perception and memory components of task performance. The results suggest that applications employing multielement codes or signage may benefit from grouping together related or the most critical items. Most notably, this benefit would be as large or larger for the old than for the younger user populations.

Adolescent↗