The effect of attention on the auditory steady-state response.

40-Hz auditory steady state responses to amplitude modulated tones were recorded with magnetoencephalography to investigate the effect of focused attention. A modulation discrimination task and a destructive visual task established the attended and the non-attended experimental conditions. A strong contrast between these conditions was demonstrated by largely enhanced sustained responses under the attention condition. A significant attentional effect on the ASSR amplitude was observed mostly in the left hemisphere between 200 to 500 ms after stimulus onset. In contrast, transient gamma-band and N1 responses were not affected by the different states of attention.