Abstract

The evaluation of vigilance would be facilitated by using brief and self-paced simple tests. Recently, we developed and tested a pencil and paper task - a Letter Cancellation Task (LCT) - requiring the search for letter targets within a matrix of alphanumeric stimuli written with the same character fonts. Previous results showed that this LCT is sensitive in revealing the effects of time of day and of 24 hours of sleep deprivation. In the present study we assessed the sensitivity of two forms of the LCT respectively with 2- (2L) and 3-target letters (3L) in revealing the effects of time of day, considering performance on LCT with a fixed completion time (5 min.) or without a time limit. In addition, we evaluated time of day effects on six Visual Analogue Scales (VAS) measuring subjective activation-deactivation. Results showed that both LCT.2L and LCT.3L with or without a fixed time are able to reveal effects of time of day, but a grater sensitivity was shown by LCT.3L with a fixed time. Furthermore, results indicated that performance was lower when a fixed time of 5 min. was allowed with respect to condition in which no time limit was given, and that attentional load modulated difficulty of the task, with higher proportion of hits on LCT.2L than to LCT.3L. Effects of time of day were also revealed by VAS data. The present study confirm that both LCT and VAS can be advantageously used for evaluating vigilance in studies requiring the testing of many subjects and in field studies in which the use of a brief self-paced performance task allows minimizing the intrusiveness of the measurement on the people studied.