A double interference Stroop task: effect of nocturnal alertness reduction

This study points to evaluate the effect of a reduction of alertness, obtained by sleep reduction as well as circadian phase, on the inhibition of automatic behavior to allow a voluntary one. One of the most used task to this purpose is the Stroop Task (Stroop, 1935). In the scientific literature mixed results have been reported about this subject (Sagaspe et al., 2006). Methods: A modified version of the Stroop Task has beenused (Besner & Stolz (1999). Stimuli were words naming colors, and letters compounding them were colored in two different colors. Participants have to name the central letter’s color, which was congruent or incongruent as respect to the meaning of the word (e.g. rosso, Italian word for red, presented with the central S in red or in green). The other letters were in a different color as respect to the central letter. One hundred and fifty millisecondsearlier the word presentation, a small circle (spatial cue), surrounded the central letter (valid condition), the letter on the right or the left of the central one (invalid condition) or the entire word (neutral condition). Participants have been invited to ignore the cue. Participants have performed the task at 12.00 p.m. and 2.00 a.m. Results: An ANOVA 2 Session · 2 Conflict · 2 Cue on the average of the vocal responses (RT) has revealed main effects of Session (F1,8 = 11,45; P < 0.01), Conflict (F1,18 = 23,9; P < 0.001), and Cue (F3,24 = 13,86; P < 0.001). The Session · Cue (F3,24 = 3,36; P < 0.03) interaction was also significant. In the Night Session RT were slower in the invalid condition (664 ms) as respect to the valid condition (620 ms; P < 0.00004). Conclusion: Reading a word and the attentional capture by a spatial cue have been considered as automatic process, which must be inhibited to allow the voluntary task of naming the central letter’s color. In the task presented here there was no need to move the focus of attention from the center of the word, because the color of the letter to be named was always presented in the same position. Nevertheless, in the night session, Participants seem to be more sensitive to the effect of the attentional capture exerted by invalid cue.