Robertson, Manly, Andrade, Baddeley, and Yiend (1997) have proposed that detection failures in vigilance tasks result from a 'mindless' withdrawal of attentional effort from the monitoring assignment. To explore that view, they modified the traditional vigilance task, in which observers make button-press responses to signify the detection of rarely occurring critical signals, to one in which button-press responses acknowledge frequently occurring non-signal events and response withholding signifies signal detection. This modification is designed to promote a mindless withdrawal of attentional effort from the task through routinization. The present study challenges the validity of the mindlessness model by showing that with both types of task, observers utilize subtle patterns in the temporal structure of critical signal appearances to develop expectations about the time course of those appearances that affect performance efficiency. Such expectations enhance performance on the traditional vigilance task, but degrade performance on the modified task.

Transcranial Doppler sonography (TCD) and transcranial cerebral oximetry (TCCO) measures of cerebral blood flow velocity and oxygenation levels were collected during an abbreviated 12-min vigilance task. Both the TCD and TCCO measures showed higher levels of cerebral vascular activity in the right than in the left cerebral hemisphere; the cerebral laterality of vigilance occurs in an abbreviated task. Although there was a significant decline in performance over time, there was no significant change in the physiological measures over time during the abbreviated vigil. This latter finding does not match the physiological changes detected in long-duration vigils.

Signal ~~ord.s, such as DANGER and WARNING have been used in print (visual) warnings with the intention of evoking di&ed levels of perceived hazard. However, there is limited research on whether auditory presentation of these words connote different levels of perceived hazard. In the present study, ,fivc voiced signal words were used to produce sound clips each composed of the words spoken three times and x~ere manipulaled according to the following factors: speaker ge~&r, word unit duration (fast, slow), inler-word interval, (short, long), with the sound level held constant. Results indicate that the sound clips with sh~rl word unit duration were given higher carefulness ratings than long +yord unit duration @s < .Ol). The results showed a similar pattern of ratings for the signal words as shoxrn in research using print presentations. Implications for the design of voiced warnings are described.

No abstract

The signal regularity effect — enhanced performance efficiency when critical signals for detection appear in a temporally regular as opposed to an irregular manner- has a long history in vigilance research. However, the precise conditions under which this effect can be elicited have not been identified. Toward that end, this study demonstrates that the effect is limited to low salience signals, perhaps because the effort needed to generate veridical temporal expectancies is unnecessary with high salience signals. Additionally, using signal detection theory indices ( d' & c) and neuroimaging of cerebral blood flow via transcranial Doppler sonography, this study also shows that the signal regularity effect is rooted in sensing rather than decision-making factors and that it is localized in the right cerebral hemisphere.

Observers monitored displays of five circles for the presence or absence of a line in one of the circles during a 40-min vigil. Displays were updated 6, 12, or 24 times/min (event rate). Signal detections varied inversely with event rate when observers monitored for the absence of the distinguishing feature but not when monitoring for the presence of that feature and judged the workload of their assignment to be greater when monitoring for feature absence than presence. In addition, the availability of information processing resources, as indexed by transcranial Doppler sonography measurements of cerebral blood flow, was exhausted more rapidly when observers monitored for feature absence than for feature presence. This effect was limited to the right hemisphere. The results are consistent with the view that detecting feature absence is more capacity demanding than detecting feature presence and with previous brain imaging findings indicating right hemispheric control of vigilance.Search asymmetry is a well-established finding in brief attention tasks (Quinlan 2003;Treisman & Gormican, 1988). This effect refers to more rapid detections when searching for the presence of a distinguishing feature in an array of stimuli as opposed to its absence. Indeed, when searching for presence, the distinguishing feature appears to be so salient that it seems to "pop out" of the display. The phenomenon of search asymmetry has been accounted for by the feature integration model (Treisman & Gormican, 1988) which suggests that searching for the presence of a feature is guided by preattentive, parallel processing while more deliberate, serial processing is required for determining its absence.Studies by Schoenfeld and Scerbo (1997;1999) have extended the presence/absence distinction to the accuracy of signal detections in long-duration sustained attention or vigilance tasks. Performance efficiency in vigilance tasks varies inversely with the information-processing demand imposed by the task as indexed by the number of stimulus elements that must be scanned in search of critical signals (Grubb, Warm, Dember, & Berch, 1995). The view that detecting the absence of a feature is more capacity demanding than detecting its presence led Schoenfeld and Scerbo (1997;1999) to predict that increments in the number of array elements to be scanned in separating signals from noise in vigilance would have a more negative effect upon signal detection in the stimulus absence than in the stimulus presence case and that perceived mental workload would be greater when critical signals for detection were defined in terms of feature absence than presence. Consistent with those predictions, they found that when observers were required to detect the absence of a feature, signal detectability declined as the size of the stimulus array was increased from two to five elements. Increasing array size, however, had no effect on performance when observers were required to monitor for the presence of that feature. In addition, observers rated the workload of their ...

Using Transcranial Doppler sonography, cerebral blood flow velocity (hemovelocity, CBFV) was recorded from the middle cerebral arteries during the performance of 40-min auditory and visual vigilance tasks. Reductions in stimulus duration were the critical signals for detection in both tasks, which were equated for stimulus salience and discrimination difficulty. Signal detection responses (correct detections and false alarms) and CBFV declined linearly over time in both modalities. In addition, the overall level of CBFV and the temporal decline in this measure were greater in the right than the left cerebral hemisphere. The results support the view that a right hemispheric system is involved in the functional control of vigilance and that this system operates in a similar manner in the auditory and visual channels.Vigilance or sustained attention concerns the ability of observers to detect infrequent and unpredictable signals over prolonged periods of time. This aspect of human performance is important to human factors/ergonomic specialists because of the critical role that vigilance occupies in automated human-machine systems such as air-traffic control, cockpit monitoring, airport baggage inspection, nuclear power plant regulation, and industrial-process/quality control (Davies & Parasuraman, 1982: Hancock & Hart, 2002Wickens & Hollands, 2000). Hence, knowledge of the factors that control vigilance performance and their underlying neurophysiological mechanisms is critical for system reliability and productivity and for public safety (Nickerson, 1992;Warm & Dember, 1998).Investigations using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) procedures have been successful in demonstrating that changes in cerebral blood flow and glucose metabolism are involved in the performance of sustained attention or vigilance tasks (Parasuraman, Warm, & See, 1998). These studies identified multiple brain regions that are active during the performance of such tasks, including the frontal lobes, the cingulate gyrus, the intralaminar region of the thalamus, and the midbrain reticular formation. However, as Parasuraman et al. (1998) emphasized, an important limitation of these studies is their failure to correlate brain activity with performance efficiency, perhaps due to the high costs and restrictive environments associated with PET and fMRI. Thus, the functional role of the brain systems identified in the imaging studies remains largely unknown. Gazzaniga, Ivry, and Mangun (2002) have also underscored the importance of linking neuroimaging results to performance efficiency for enhanced understanding of research in cognitive neuroscience.The high costs and the restrictions of PET and fMRI may be circumvented in studying brain systems in vigilance by employing transcranial Doppler sonography (TCD) -a relatively inexpensive and noninvasive procedure that allows for continuous monitoring of cerebral blood flow velocity (CBFV) in the main-stem intracranial arteries. When an area of the brain becom...

No abstract