Cross-modal multitasking processing deficits prior to the central bottleneck revealed by event-related potentials.

We investigated whether concurrent processing of a tone (T1) interferes with early sensory-perceptual processing of a visual target (T2) in variants of the psychological refractory period paradigm using the event-related potential (ERP) method and 70-channel electroencephalographic recordings. T1, which required a speeded response, was presented in all trials. In half of the trials, T1 was followed by a bilateral visual display, T2, which also required a speeded response. A single T1-T2 stimulus onset asynchrony was adjusted dynamically to maximize task overlap in a hard-Task1 condition while minimizing task overlap in an easy-Task1 condition. The ERP to T1 in trials with only T1 presented (uncontaminated by T2) enabled us to subtract T1-related activity from the dual-task T2-locked ERPs. An attenuation of the T2-locked occipital N1 was observed in the hard-Task1 condition, relative to the easy-Task1 condition, both when T2 required a discriminative response and a detection response. An attenuation of the visual P1 component was also observed when T2 required a discriminative response. The N2pc was also attenuated, and the sustained posterior contralateral negativity (SPCN) was delayed, by concurrent processing in the discrimination task. Implications for models of dual-task interference are discussed.