DOES THE APPARITION MOMENT OF MENTAL FATIGUE VARY AS A FUNCTION OF AGE? INVESTIGATION OF TIME-ON-TASK EFFECT IN YOUNG, MIDDLE-AGED, AND OLDER PEOPLE

Introduction.
Young people show an increase in their reaction time (RT) between the first and the last 40 minutes of a 160-minute Stroop task (Wang et al., 2016). Our study is aimed at replicating Wang et al. (2016) results but also to test for the first time this Time-on-Task effect in middle-aged and older people.
Method.
Twenty-one Young (MAge=21.29), 17 Middle-aged (MAge=50.47), and 17 Older (MAge=65.06) performed a 160-minute Stroop task comprising facilitator (FA), interfering (I), and neutral (NE) items, these later ones systematically appearing one out of two. The total duration was divided into eight blocks of 20min. with the elimination of the Block 0 (habituation block). 3(Groups) X 7(Blocks) repeated measures ANOVAs were carried out on mean and coefficient of variation (CV) of the RT.
Results.
Mean. The Young showed a RT increase between the 1st and the 5th block on NE items (p=.026) while this increase appeared in Block 4 for Middle-aged (p=.001) and Older (p=.042).CV. Young showed an increase in CV between the 1st and the 7th block (p=.002) on NE items while Middle-age showed this increase on the 6th block (p=.03). By contrast, Older did not significantly vary in their CV.
Discussion.
Mental fatigue triggered by Time-on-Task in aging seems to manifest by a general slowdown of information processing: Middle-aged and Older being more quickly exhausted as compared to Young. However, while Young and Middle-aged seem to be affected in their CV, more advanced aging seems to preserve intra-individual variability from Time-on-task.