Monaural loudness adaptation for middle-intensity middle-frequency signals: the importance of measurement technique.

Using the Simple Adaptation technique (SA) and the Ipsilateral Comparison Paradigm (ICP), the authors studied monaural loudness adaptation to a middle-intensity [60 dB(A)] tone at signal frequencies of 250, 1000, and 4000 Hz in the left and right ears. Adaptation effects were absent when the SA procedure was used. However, they were observed uniformly across all frequency values with the ICP, a result that challenges the assertion in the literature, on the basis of SA measures, that loudness adaptation for middle-intensity signals occurs only at frequencies above 4000 Hz. The ICP features periodic intensity modulations (+/-10 dB relative to the base signal) to accommodate listeners' needs for referents by which they can gauge subtle changes in the loudness of the adapting tone, a key component that is missing in the SA method. Adaptation effects in this investigation were similar in both ears, supporting the equal susceptibility assumption common in loudness adaptation studies.

Subjective organization and the visibility of illusory contours.

The effects of the differential organization of a Necker cube on the perceived salience of an embedded illusory triangle were examined. Overall figural salience was greater when the triangle appeared to be localized on the front rather than the back cube face. Illusory contour salience also increased with increasing inducing area contrast and was greater when the figure was oriented on cardinal as compared to oblique coordinates. However, the latter effects were independent of perceived location within the cube. The finding that subjective organizational and structural factors influenced the perceived salience of the illusory figure but did not interact is consistent with van Tuijl and Leeuwenberg's (1982) suggestion that top-down and bottom-up determinants can operate independently in illusory contour perception.

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).

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.

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.

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.

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.

Recent advances in the neuropsychology of human olfaction and anosmia.

Patients' olfactory functioning is rarely considered by rehabilitation specialists because this capacity is seen as unnecessary for most vocational and academic purposes. However, several recent studies have shown that intermittent exposure to fragrances can help subjects sustain attention more efficiently. As this effect is especially pronounced when subjects report attention-maintenance difficulties, accessory olfactory stimulation may enhance the sustained attention capacities of head-injured subjects. Another study is cited in which subjects who lost their sense of smell following head injuries were found to experience more difficulty in maintaining employment. This effect is probably related to orbital lobe damage, which usually accompanies post-traumatic anosmia. The implications of these studies for rehabilitation professionals are discussed.

Effects of jet engine noise and performance feedback on perceived workload in a monitoring task.

This study examined the effects of exposure to intermittent jet aircraft noise (70 dBA or 95 dBA maximum intensity) and knowledge of results concerning signal detections (hit-KR) on performance efficiency and perceived workload in a 40-min visual vigilance task. The noise featured a Doppler-like quality in which planes seemed to approach from the monitor's left and recede to the right. Perceptual sensitivity (d') was poorer in the context of noise than in quiet but only in the presence of hit-KR. The lack of noise-related performance differences in the absence of hit-KR most likely reflected a "floor effect" rather than some special relation between noise and feedback. When compared to subjects performing in quiet, those who operated in noise were less able to profit from hit-KR, a result that may reflect the effects of noise on information processing. In addition to its negative effects on signal detectability, noise elevated the perceived workload, as measured by the NASA-TLX. This effect was robust; it was independent of the presence of hit-KR, even though hit-KR generally lowered the overall level of perceived workload. The results provide the initial experimental demonstration that perceived workload is a sensitive measure of the effects of aircraft noise in monitoring tasks.

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.

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.

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.

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.

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.

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.

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.

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.

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.