COMBINED EFFECTS OF MENTAL LOAD AND BACKGROUND-NOISE ON CNS ACTIVITY INDICATED BY BRAIN DC POTENTIALS

To assess combined effects of noise and mental load on brain activity, DC potential shifts were evaluated. In a 4-way repeated analysis of v ariance (ANOVA) design with Type of Noise, Sound Intensity, Mental Loa d, DC Recording Location as factor, 2-min epochs of noise exposure wer e compared in 18 subjects. Significant main effects were found for Typ e of Noise (white noise and street noise showing greater positive shif ts than music sound), Mental Load (more positive shifts for mental loa d vs. no mental load), and DC Recording Location. Statistically signif icantly higher order interaction effects were also found. Low intensit y of music sound diminished the mental load CNS activity (DC shifts), interpreted as a possible compensatory effect of soft music on mental load. The effect of mental load under street noise and white noise con ditions depends on the CNS activity (DC shifts) caused by these backgr ound noises alone, showing a ceiling effect. Results indicate that CNS activity (DC shifts) apparent during mental load are changed by acous tic stimulation additionally applied and that this effect is dependent on type of noise/sound and sound intensity.