Activation of brain mechanisms of attention switching as a function of auditory frequency change.

The activation of the cerebral network underlying involuntary attention switching was studied as a function of the magnitude of auditory change. Event-related brain potentials (ERPs) were recorded during the performance of a visual discrimination task in which task-irrelevant auditory frequency changes of six different levels (5%, 10%, 15%, 20%, 40% and 80%) occurred randomly within the same stimulus sequence. All the frequency changes elicited a typical ERP waveform, characterized by MMN, P3a and RON, their respective amplitudes increasing linearly as a function of the magnitude of change. The results indicate that attentional processes in the brain may follow a linear function of activation, contrasting with the well-established logarithmic functions underlying perceptual and psychophysical processes.