Did You Listen to the Beat? Auditory Steady-State Responses in the Human Electroencephalogram at 4 and 7Hz Modulation Rates Reflect Selective Attention.

Abstract

The acoustic envelope of human speech correlates with the syllabic rate (4-8Hz) and carries important information for intelligibility, which is typically compromised in multi-talker, noisy environments. In order to better understand the dynamics of selective auditory attention to low frequency modulated sound sources, we conducted a two-stream auditory steady-state response (ASSR) selective attention electroencephalogram (EEG) study. The two streams consisted of 4 and 7Hz amplitude and frequency modulated sounds presented from the left and right side. One of two streams had to be attended while the other had to be ignored. The attended stream always contained a target, allowing for the behavioral confirmation of the attention manipulation. EEG ASSR power analysis revealed a significant increase in 7Hz power for the attend compared to the ignore conditions. There was no significant difference in 4Hz power when the 4Hz stream had to be attended compared to when it had to be ignored. This lack of 4Hz attention modulation could be explained by a distracting effect of a third frequency at 3Hz (beat frequency) perceivable when the 4 and 7Hz streams are presented simultaneously. Taken together our results show that low frequency modulations at syllabic rate are modulated by selective spatial attention. Whether attention effects act as enhancement of the attended stream or suppression of to be ignored stream may depend on how well auditory streams can be segregated.