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Biomedical subjects

W N Dember

Publications and source records attributed to W N Dember.

At least 19 recordsLinked to original sources
PubMed2000

Ipsilateral loudness adaptation over multiple intensity levels.

Could monaural loudness adaptation be a simple artifact of psychophysical contrast? From adaptation data based on the Ipsilateral Comparison Paradigm (ICP), A. J. Dange, J. S. Warm, E. M. Weiler, and W. N. Dember (1993) concluded that loudness adaptation was not an artifact of psychophysical contrast, but their conclusion was dependent on results from one intensity. This study, involving multiple intensities, re-examined the issue of contrast versus adaptation and generally supported the conclusions of Dange et al. The results also showed an unexpected asymmetry of adaptation based on the direction of the referent modulation used with the ICP technique. Some implications are discussed.

Adaptation, Physiological↗
PubMed2000

The effects of signal salience and caffeine on performance, workload, and stress in an abbreviated vigilance task.

In 2 experiments, a 12-min computerized vigilance task was demonstrated to reproduce the vigilance decrement, high workload (NASA-TLX), and stressful character (Dundee Stress State Questionnaire) of vigilance tasks lasting 30 min or more. In Experiment 1, the abbreviated task was also shown to duplicate the signal salience effect, a major finding associated with long-duration vigilance tasks. Moreover, Experiment 2 showed that performance on the abbreviated task can be enhanced by caffeine - a drug that benefits long-duration tasks. This enhancement effect was limited to performance, however, suggesting that caffeine influences factors that control signal detection but not those that control task-induced stress. The results parallel those obtained with long-duration tasks and support a resource-depletion model of the vigilance decrement. The abbreviated task might be useful in situations in which long-duration tasks are precluded (e.g., performance assessment batteries, neuropsychological testing, and brain imaging).

Adolescent↗
PubMed1999

Effects of cueing and knowledge of results on workload and boredom in sustained attention.

Two models of recently reported high workload associated with vigilance tasks are the direct-cost and indirect-cost views. The former attributes high workload to the need for continuous observation in discriminating signals from neutral events; the latter attributes it to efforts to combat the boredom associated with monotonous vigilance tasks. These opposing views were tested by providing observers with reliable cueing, which rendered observation necessary only when low-probability critical signals were imminent, or with knowledge of results (KR) regarding performance efficiency. On the basis of cue and KR differences in elicited observation activity and motivational value, the direct-cost model led to the anticipation that cueing would result in a high-boredom, low-workload profile and a greater reduction in workload than KR. The indirect-cost model led to the prediction that cueing would result in a high-boredom, high-workload profile and a lesser reduction in workload than KR. The results clearly supported the direct-cost view that the workload of vigilance is task-induced. Consequently, efforts to combat high workload in complex automated systems requiring substantial monitoring by operators should focus specifically upon task-related determinants.

Acoustic Stimulation↗
PubMed1998

Effects of olfactory stimulation on the vigilance performance of individuals with brain injury.

Observers with brain injury and control participants performed a vigilance task during which they received periodic whiffs of unscented air or air scented with peppermint. Under both fragrance conditions, controls reduced the frequency of commissive errors (false alarms) over the course of the vigil, an adaptive strategy given the low probability of signals employed (0.04). The false alarm rate of observers with brain injury increased precipitously toward the end of the vigil in the unscented air condition. However, exposure to the scent of peppermint rendered the false alarm scores of observers with brain injury similar to that of controls, a result which is consistent with evidence that olfactory stimulation activates brain areas vital for planning and judgment.

Adolescent↗
PubMed1996

Mood and global-local visual processing.

Testing hypotheses derived from neuropsychological models of mood, as well as the association of mood states and personality characteristics with global-local visual processing, were examined. Fifty-nine men completed measures associated with depression and positive mood, and were administered a brief perceptual judgment task that assessed global-local visual processing biases. Additionally, 19 of these 59 subjects were administered measures of anxiety and optimism-pessimism and completed an expanded judgment task. Affective and personality variables were then correlated with judgment task performances. Consistent with predictions, positive mood and optimism were directly associated with a global bias and inversely related to a local bias. A converse pattern of findings was obtained with depression and trait anxiety. Implications for research concerning other aspects of visual processing are discussed.

Adult↗
PubMed1994

Closed head injury assessment and research methodology.

About two million Americans incur head injuries each year, resulting in approximately 50,000 chronic disabilities. Several methods are currently used to determine the physiological changes underlying behavioral sequelae commonly associated with closed head injuries. Structural assessment techniques, including lesion studies, standard radiographs, computed tomography and magnetic resonance imaging, are used to determine the physical integrity of brain structures. Functional assessment techniques, including neuropsychological methods, the electroencephalograph, evoked potentials and positron emission tomography, are used to examine the brain through an analysis of its behavioral, electrical and chemical outputs. Accurate head injury assessment is vital for diagnosis, treatment planning and research. Injuries are commonly divided into the categories of mild, moderate and severe based on duration and depth of coma and the length of posttraumatic amnesia. Application of these severity assessment parameters is currently being improved through the use of standardized assessment measures.

Animals↗
PubMed1994

Determinants of stability in the perception of subjective contours.

The present study constituted an initial experimental effort to examine the fragmentation characteristics of subjective contours within the photopic and upper scotopic ranges of illumination. Four stimulus factors known to influence the visibility of subjective contours-target luminance, inducing area size and contrast, and contour orientation--were examined. Results indicated that subjective contours are indeed unstable perceptual phenomena. On the average, fragmentation or fading occurred after only 15 sec of observation, and some form of stimulus outage was present for 28% of the viewing time of each stimulus. Fragmentation latency was significantly shorter and total time in fragmentation longer for diamond than for square contours, and total time in fragmentation varied inversely with inducing-area size. Fragmentation tended to occur in whole units rather than in isolated elements, a result reminiscent of the fading of real contours under impoverished viewing conditions.

Form Perception↗
PubMed1993

Loudness adaptation: resolution of a psychophysical enigma.

Traditional measurement of loudness adaptation based on binaural matching has been challenged by Scharf (1983) and others as an artifact of binaural interaction due to contrast effects. Weiler, Sandman, and Pederson (1981) addressed this problem by developing a monaural technique called the ipsilateral comparison paradigm (ICP), which demonstrates strong adaptation effects within the auditory system. The two experiments described in this report support the meaningfulness of that procedure. They show that the ICP is not confounded by psychophysical contrast as suggested by Canevet, Scharf, and Botte (1983); they also demonstrate that the results obtained with the ICP are robust--adaptation effects were noted across a broad range of intensities and were similar when psychophysical reports were made by magnitude estimation and graphic rating means.

Acoustic Stimulation↗
PubMed1993

Sex differences in vigilance performance and perceived workload.

Female and male subjects monitored the repetitive presentation of a pair of lines for occasional changes in height (spatial task) or duration (temporal task). Perceptual sensitivity for critical signals favored men in the spatial task, whereas no sex differences in signal detectability existed in the temporal task. Measurements of perceived workload using the NASA-TLX scale mirrored these performance effects. Women tended to rate the overall workload associated with the spatial task to be greater in comparison with men. In addition, women found the spatial task to be significantly more frustrating, mentally demanding, and effortful than men did and rated their own performance lower than their male counterparts did. In contrast, no sex-linked differences in perceived workload were noted in regard to the temporal task. The results support the suggestion by Dittmar, Warm, and Dember (1987) that sex differences in sustained attention are task specific.

Adolescent↗
PubMed1993

Demand transitions and sustained attention.

A recent report by the National Research Council (Huey & Wickens, 1993) has identified transitions in task demand as an important dimension for study in vigilance research. This experiment tested the possibility that the effects of such transitions follow a relatively simple psychophysical rule--they are characterized by contrast effects. Transitions in task demand were achieved by shifting subjects from single-task to dual-task monitoring and vice versa. These transitions produced changes in subjects' sensing and decision-making functions that were far more intricate than simple contrast effects. The demand transition issue offers a complex research challenge on both basic and applied levels and warrants further investigation.

Adult↗
PubMed1993

Psychophysical determinants of stress in sustained attention.

To date, research on the stress of sustained attention tasks has not explored the extent to which such stress is determined by the psychophysical aspects of the monitored display. In the present study, the effects of the sensory modality of signals (audition and vision) and the background event rate (5 and 40 events/min) on task-induced stress were examined in a vigilance situation. Critical signals for detection were slight changes in stimulus duration. Stress was indexed by motor restlessness and subjective reports of fatigue. Restlessness and subjective fatigue increased dramatically across a 50-min watch in all conditions. Stress effects were most notable in the case of visual monitoring but were unrelated to variations in event rate. Hence, from a psychophysical perspective, the stress of sustained attention seems to be identified more specifically with the sensory modality of signals than with the event rate context in which they appear.

Adolescent↗
PubMed1990

Sensory alternation and vigilance performance: the role of pathway inhibition.

Posner's theory of pathway inhibition leads to the expectation that stimulus heterogeneity should attenuate the event rate effect and the decrement function in sustained attention. These predictions were tested through a sensory alternation procedure in which stimulation was shuttled between the auditory and visual modalities. Subjects detected slight reductions in the duration of recurrent flashes of light or bursts of white noise at two event rates (5 and 40 events/min) during a 50-min vigil. Consistent with the model, sensory alternation eliminated the event rate effect. It did not, however, moderate the decrement function. Although pathway inhibition can account for the effects of event rate, other factors are probably responsible for the vigilance decrement.

Adolescent↗
PubMed1987

Effects of head restraint on signal detectability in simultaneous and successive vigilance tasks.

Dittmar, Warm, and Dember (1985) suggested that visual parallax may lead to declines in perceptual sensitivity over time in spatial vigilance tasks involving comparative judgments. The present study tested this possibility by restraining subjects' head movements during a 1-hr vigil in which comparative (simultaneous task) or absolute (successive task) judgments of line length were necessary for signal detection. Under free-viewing conditions, perceptual sensitivity declined over time with both types of tasks. Head restraint eliminated the sensitivity decrement in both cases. The results highlight signal quality as a crucial determinant of perceptual decrements in sustained attention.

Attention↗
PubMed1983

Target recovery in visual backward masking: no clear explanation in sight.

Theories of visual backward masking have generally ignored demonstrations of the perceptual recovery of a masked target when the masking stimulus (M1) is followed by a second masking stimulus (M2). This failure to address recovery may reflect a belief that recovery effects are relatively small and inconsistent. The present article reports a series of experiments, using single-letter targets, a patterned M1 and a light-flash M2, which indicate that recovery can be a robust and substantial phenomenon. It is observable under a variety of conditions, and the magnitude of recovery matches the masking effect itself. A two-choice discrimination task was employed to test an explanation for recovery that attributes the effect to inhibition from the transient response to the light flash on the sustained response to the patterned mask. That explanation calls for the shape of the function relating the discriminability of the patterned mask to the onset asynchrony of M1 and M2 to be U-shaped in form. The data, however, reveal a monotonic masking function, suggesting that only sustained, intrachannel interactions are involved in the recovery of the target percept. Two conflicting explanations for recovery are discussed, one based upon inhibition of M1 responses, the other upon enhancement of target features. Thus, while recovery is demonstrated to be very real, its explanation remains elusive.

Adolescent↗
PubMed1972

Backward enhancement?

Presentation of a masking stimulus enhances, rather than detracts from, detectability of certain multisegment targets. Present theories of backward masking cannot account for this "backward enhancement" effect, which resembles another puzzling phenomenon, previously reported as target recovery or disinhibition. An explanation in terms of interaction between retinal excitatory and inhibitory fields is offered.

Adult↗