Doing the math: detection and neural processing of auditory task-unrelated stimuli while solving arithmetic tasks

Load Theory proposes that perceptual load impairs the processing of task-unrelated stimuli. However, there is increasing evidence that not only perceptual demands but also cognitive task load affect the processing of task-unrelated stimuli. The current event-related potential (ERP) study investigated the effects of cognitive load induced by arithmetic operations on the detection and neural processing of intensity-modulated beep tones. The tasks were based on different instructions regarding perceptually identical displays of numbers. Results showed decreased stimulus detection and reduced P3b in the ERP to auditory stimuli under high compared with low load across different signal-to-noise ratios (SNR). However, the N1 amplitude was unaffected by load based on our typical analytical pipeline using an average reference. Using a linked mastoids reference and strong filtering revealed an effect of load on the N1 for the highest SNR. Thus, analytical pipelines may affect the results. Nevertheless, the lower probability of reported awareness of task-unrelated auditory stimuli during difficult mathematical tasks across SNR levels seems to be driven predominantly by a late neural effect.