Biomedical subjects

A F Kramer

Publications and source records attributed to A F Kramer.

At least 55 records · Page 3Linked to original sources

PubMed1996

Aging and filtering by movement in visual search.

We examined the ability of younger and older adults to selectively process moving items and ignore stationary items in a task that required the search for a target defined by a conjunction of movement and form (i.e., search for a moving X among moving Os and stationary Xs) in displays of 5, 9, 17, and 25 stimuli (Experiment 1) and displays of 5, 10, and 20 stimuli (Experiment 2). We also investigated subjects' performance in two feature search tasks, the search for a target defined by movement or form. Finally, we examined the influence of practice on feature and conjunction search. Younger and older adults searched the displays at similar rates in the feature and conjunction search tasks. Older and younger adults also benefited equivalently from practice. These data suggest age-equivalence in the processes which underlie feature search in dynamic environments as well as those processes responsible for the segregation of moving and stationary objects in the visual field.

Adolescent↗

PubMed1995

Event-related potentials as indices of display-monitoring performance.

We evaluated event-related potentials (ERP) as indices of performance in three visual display-monitoring tasks: (a) signal detection, (b) running memory and (c) computation. Using factor analysis, we developed a global measure of performance (PFI) for each task. Task-relevant and irrelevant-probe stimuli elicited ERPs, which included components P1, N1, P2, P300, slow waves, and fronto-central negativities. In tasks (a) and (b), P300 amplitude in the task-relevant ERPs increased when the task was engaged, and was greater for accurate-than for inaccurate-response trials. In tasks (a) and (c), the irrelevant-probe ERPs also differed among task and performance conditions. To relate ERP measures to PF1, we developed linear regression models distinguished by three factors: general versus individual-subject, stimulus relevance, and signal-to-noise ratio (SNR). Model accuracy and reliability were highest for individual-subject, relevant-stimulus and high-SNR models, where average R2 values for the three tasks were 0.44, 0.46, and 0.38, respectively. We discuss implications of the models for performance monitoring and implications of the ERP effects for human information processing.

Adult↗

PubMed1995

Assessment of mental workload with task-irrelevant auditory probes.

A study was performed to examine the utility of an ERP-based irrelevant probe technique for the assessment of variations in mental workload. Ten highly trained Navy radar operators performed a simulated radar-monitoring task which varied in the density and type of targets to be detected and identified. This task was performed in the presence of a series of irrelevant auditory probes which the radar operators were instructed to ignore. Prior to performing the radar-monitoring task the subjects performed a block of auditory detection trials in which they were asked to respond to the occurrence of one of two low probability tones and ignore the other low probability tone along with a higher probability standard tone. ERPs were recorded from the occurrence of the tones in both the baseline and low and high workload radar-monitoring conditions. The amplitude of the N100, N200, and early and late mismatch negativity (MMN) components decreased from the baseline to the low load radar-monitoring task and again with an increase in the difficulty of the radar-monitoring task. P300 amplitude was sensitive only to the introduction of the radar-monitoring task. These results are interpreted with respect to the phenomenon of attentional capture and suggest that the ERP-based irrelevant-probe technique might prove an effective method for the nonintrusive evaluation of increases in mental workload in complex tasks.

Adult↗

PubMed1995

Attentional flexibility and aging: you don't need to be 20 years of age to split the beam.

Whether young and old adults were able to selectively attend to noncontiguous locations in the visual field and ignore physically interspersed distractor stimuli was examined. Participants decided whether 2 letters matched or mismatched. Target letter locations were precued by square boxes on an imaginary circle centered on fixation. Distractors were located between the 2 targets. Young and old were unable to ignore the distractors when the targets and distractors were presented as onset stimuli; however both young and old were able to ignore the distractors when the target and distractors were presented as non-onset stimuli. The time course of attentional allocation was equivalent for young and old. Results are discussed in terms of models of visual selective attention and the flexibility of attentional control.

Adolescent↗

PubMed1995

Attentional modulation of the mismatch negativity elicited by frequency differences between binaurally presented tone bursts.

We examined the attentional sensitivity of the frequency-change mismatch negativity (MMN). Subjects listened to a binaural mixture of a narrative and a series of tone bursts that included 1200-Hz standards and two deviants (1000 and 1400 Hz). In the attend-tones condition, subjects responded to one deviant and ignored the narrative. In the attend-words condition, subjects responded to target words in the narrative and ignored the tones. Event-related potentials (ERPs) were recorded for the tones, and difference waves (deviant ERPs minus standard ERPs) were computed. Two negative peaks in the difference waves, DN1 (100-180 ms) and DN2 (200-300ms), overlapped the known scalp distribution and latency of the MMN. Mean DN1 and DN2 amplitudes were greater in the attend-tones condition than in the attend-words condition. These suggest that the frequency-change MMN is modulated by nonspatial shifts of auditory attention.

Acoustic Stimulation↗

PubMed1994

Aging and skill acquisition: learning-performance distinctions.

This research examined the hypothesis that a conservative response bias in older persons interferes with the acquisition and mastery of cognitive skill. Twenty younger and 20 older Ss performed both consistent mapping and varied mapping versions of a memory search task. Half of the Ss in each group performed under speed stress instructions, whereas the remaining Ss performed under accuracy stress instructions. Older Ss exhibited less skilled performance than did younger Ss. A power function analysis attributed this to both age-related differences in the rate of associative learning and differences in asymptotic levels of performance. These results are at odds with A. D. Fisk and W. A. Roger's (1991) hypothesis that age-related differences in automatization do not occur in memory search tasks. Results are interpreted in terms of a learning vs. performance distinction.

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

Attentional misguidance in visual search.

Previous research has shown that a task-irrelevant sudden onset of an object will capture an observer's visual attention or draw it to that object (e.g., Yantis & Jonides, 1984). However, further research has demonstrated the apparent inability of an object with a task-irrelevant but unique color or luminance to capture attention (Jonides & Yantis, 1988). In the experiments reported here, we reexplore the question of whether task-irrelevant properties other than sudden onset may capture attention. Our results suggest that uniquely colored or luminous objects, as well as salient though irrelevant boundaries, do not appear to capture attention. However, these irrelevant features do appear to serve as landmarks for a top-down search strategy which becomes increasingly likely with larger display set sizes. These findings are described in terms of stimulus-driven and goal-directed aspects of attentional control.

Adolescent↗

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↗

PubMed1993

Assessment of pilot performance and mental workload in rotary wing aircraft.

This research examined the processing demands imposed upon experienced pilots by two different communication formats, digital and verbal, in a high fidelity simulation of an advanced multi-function helicopter. The mental workload imposed by the type and magnitude of communications was assessed by a battery of subjective, performance, secondary, and physiological measures. The performance data indicated that the pilots had difficulty adhering to the Nap of the Earth altitude criterion with high communication demands, particularly with the digital communication system. This was presumably due to the requirement to spend more time scanning the multi-function displays with the digital than with the verbal communication system. On the other hand, the pilots were less prone to task shedding when they used the digital communication system possibly due to the provision of a permanent list of queries that was unavailable with the verbal system. Measures of heart rate variability and blink rate were larger with the verbal than with the digital system, presumably reflecting increased respiratory demands in the verbal condition as well as increased visual processing demands with the digital format. Finally, the probe evoked P300 component decreased in amplitude as a function of increases in the magnitude of communications. The results are discussed in terms of the structural and capacity demands of the communications systems that were proposed for the advanced multi-function helicopter.

Adult↗

PubMed1993

Cognitive function at high altitude.

The effects of altitude on human performance and cognition were evaluated in a field study performed on Mount Denali in Alaska during the summer of 1990. Climbers performed a series of perceptual, cognitive, and sensory-motor tasks before, during, and after climbing the West Buttress route on Denali. Relative to a matched control group that performed the tasks at sea level, the climbers showed deficits of learning and retention in perceptual and memory tasks. Furthermore, climbers performed more slowly on most tasks than did the control group, suggesting long-term deficits that may be attributed to repeated forays to high altitudes.

Adult↗

PubMed1993

Limits of focused attention in three-dimensional space.

The present experiment examined the shape of the attentional gradient in three-dimensional space. Subjects performed a response-compatibility task in which they were instructed to respond to a centrally located target and ignore flanking distractors. The irrelevant distractors were presented at combinations of seven different depths, three different horizontal separations, and three different vertical separations relative to the target. Depth was varied in a stereoscopic display viewed through polarized glasses. Overall, the size of the response-compatibility effect decreased with increased separation in all three dimensions. Interestingly, the response-compatibility effect was larger for horizontal separations than for vertical separations and was larger for crossed disparities than for uncrossed disparities. The results suggest an elliptical focus of attention, with steeper gradients in the vertical dimensions than in the horizontal dimensions. In addition, the results suggest, along the vertical dimension, a steeper gradient for objects located beyond the focus of attention relative to that for objects located between the observer and the focus of attention.

Adult↗

PubMed1992

Aging, exercise, and attention.

The authors investigated the relationship among aging, attentional processes, and exercise in 2 experiments. First they examined age differences on 2 attentional tasks, a time-sharing task and an attentional flexibility task. Young adults alternated attention between 2 sequenced tasks more rapidly and time-shared the processing of 2 tasks more efficiently than older adults. They then investigated the effects of aerobic exercise on the same 2 attentional tasks in older adults. Following the 10-week exercise program, older exercisers showed substantially more improvement in alternation speed and time-sharing efficiency than older controls. Interestingly, this exercise effect was specific to dual-task processing. Both groups of subjects showed equivalent effects on single-task performance. These results indicate that aerobic exercise can exert a beneficial influence on the efficiency of at least 2 different attentional processes in older adults.

Adult↗

PubMed1992

Event related potentials and EEG components in a semantic memory search task.

This study examined the effects of memory search and related processes on both time and frequency domain components of electroencephalographic activity. More specifically, we were interested in the relationship between EEG and event-related potential (ERP) components as a function of memory load and response type. Subjects performed a semantic memory search task in which they matched word probes to category labels. Consistent with previous studies, reaction time increased and accuracy decreased with increasing memory loads. A negative component of the ERP (N400) was found to reflect semantic mismatch: N400s were larger for the nontargets than for the targets. Two ERP components were found to be reciprocally related to memory load. P300 decreased and Negative Slow Wave increased in amplitude with increases in the size of the memory set. These two ERP components were reflected by different components in a Principal Components Analysis. The power in the theta band (5-7 Hz) also increased as a function of memory load and appears to be functionally and topographically related to the Negative Slow Wave in the ERP. It is argued that both measures are jointly determined and reflect the difficulty of the conceptual operations during memory search.

Adult↗

PubMed1991

Integrated displays and the perception of graphical data.

Three experiments are presented that apply a principle of compatibility of proximity to the perception of graphical data. These experiments demonstrate that the merits and costs of integral displays relative to separable displays depend in part on the task being performed. Experiment 1 employs a data extrapolation task in which information must be integrated. Here an integral display is found to be superior to a separable display. Experiment 2 employed a data perception task that requires focused attention. This reveals superior performance with separable displays. Experiment 3 employed a multiple cue judgement task in which information integration could be manipulated. Data from Experiment 3 were analysed using the Brunswick lens procedures, and indicated that knowledge of the task structure was influenced by the display type. When selective attention was required, knowledge of the task was superior with separable displays. The results are discussed with reference to the principle of compatibility of proximity, and the implications of the results for the perception of scientific data are noted.

Adult↗

PubMed1991

Cognitive representations, control, and understanding of complex systems: a field study focusing on components of users' mental models and expert/novice differences.

Users' mental models of systems are frequently asserted to be important in their interactions with those systems. Although there are few explicit definitions of mental models in the literature, mental models are assumed to be important and researchers have seemed to accept and understand the concept intuitively. In our research, we have extracted three themes from the definitions of mental models including: (1) the relations among features or components of a system; (2) the capability of the mental model to aid in the control of the system; and (3) the capability of the mental model to enhance the user's understanding of the system. The relationships among the components of users' mental models, including procedural and declarative knowledge, perceptions of the use of system features, and the relations among the similarity of use of system features, were investigated in a field study. Trained and untrained novice users of a new business phone system rated the similarity of use of nine standard features on the phone. These ratings were used to derive cognitive representations of the relations among the system features. Users' ratings of features on univariate scales about the use of the features and scores obtained on a test of procedural knowledge were related to these representations. The two novice groups' mental models were similar except for the perception of one feature; it was more accurately depicted in the trained users' representation than those who did not attend a training programme. Two types of experts' similarity of use ratings were evaluated to determine an 'appropriate' representation of the use of the system features; this was then compared to the novices'. This comparison suggested that there were deficiencies in the mental models of novices. Designing training programmes and instructional aids for systems using the discrepancies between novices' and experts' mental models are discussed.

Adult↗

PubMed1991

Task versus component consistency in the development of automatic processing: a psychophysiological assessment.

A study was conducted to examine the role of consistency in the development of automatic processing. Subjects performed a memory search task in which consistent and inconsistent attending and responding were factorially combined. The task was performed with memory set sizes of two and four items. Results indicated that automaticity developed with consistent attending regardless of whether responding was consistent or inconsistent. However, measures of reaction time, P300 latency, and P300 amplitude revealed costs for inconsistent responding that were attributed to both stimulus evaluation and response related processes. The results suggest that total task consistency is not necessary for the development of automatic processing. Instead, it appears that automaticity can develop for consistent task components even when stimulus-response consistency is not maintained across the entire task.

Adolescent↗