Early attention effects in human auditory-evoked potentials

A fundamental question in attention theory concerns the earliest processing stages that can be modulated by selective attention. A series of experimen ts is reported in which very early attention effects are found under specif ic conditions in the frequency-following potential (FFP). a brain stem resp onse to low-frequency tone stimuli. In two experiments, stimuli of two diff erent modalities were applied, and attention directed to one of the modalit ies. In two further experiments, only auditory stimuli were presented. In t he first of these last two experiments, a dichotic paradigm with sustained attention to one ear was used, in the second a monotic paired-stimuli parad igm was used, in which the first stimulus served as reference for the secon d one. Only in the last experiment significant attention effects were found in the latency, but not in the amplitude of the FFP. The results show that a very early attention effect on the latency of the FFP can bt demonstrate d, but only under highly specific conditions. The sire and preconditions of the attention effect suggest that it reflects subtle intramodal tuning mec hanisms in the cochlea or in the lower brain stem.