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.
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.
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