Cognitive Processing dissociation and Mental Effort manipulation in long demanding tasks

Individuals uses cognitive resources to modulate performance in demanding tasks and a non-invasive and reliable way of measuring mental effort is pupillometry. This study aimed to test the mental effort related to different processing systems in long tasks with controlled and automatic demands. We conducted two experiments with healthy subjects: in Experiment 1 (n=15), using a metronome to ensure control on task pace, participants performed a serial number generation task (Counting; little to no effort tasks), a random number generation (RNG; effortful tasks), and no task (Unfilled interval; no effort at all). In experiment 2, (n=15) participants performed counting tasks with or without additional intermediary beeps produced by a metronome to assess the effect of a possible increase in effort demanded by the distractors. Experiment 1 showed differences between unfilled interval, counting and RNG. Experiment 2 showed that the intermediate beep made the counting tasks more demanding than the normal counting tasks. Notable in both experiments was the tendency of participants to demand mental effort at the beginning of the trial. These results indicate that previously effortless automatic tasks can become controlled, or at least more demanding, with a simple experimental manipulation. They also reveal that tasks that require mental effort over a long period will demand more than automatic ones, but even so the peak of this demand is in the initial trial period. Moreover, they reveal the high sensitivity of pupillometry for the measurement of mental effort employing different processing systems and cognitive resource modulation.