The same-object benefit is influenced by time-on-task

Previous studies indicated that mental fatigue particularly compromises the control of attention. To our knowledge, the present study is the first to test this notion in a divided attention paradigm that involves comparing targets placed on one versus two background objects. In general, comparing targets on two objects is less efficient than on one object because it puts more demands on divided attention. This is the well-known same-object benefit. Based on the notion of lowered control of attention under fatigue, we hypothesised that this same-object benefit becomes more pronounced in fatigued participants. We tested this with an experiment in which participants performed a visual attention task (same/different task) for 2.5 hours without rest. As a function of time-on-task, participants showed a decline in performance that was significantly more pronounced in the two object condition versus the one-object condition. These findings suggest an increased same-object benefit with time-on-task, which is likely due to compromised divided attention under fatigue.