EEG responses to natural and artificial auditory stimuli: a 40 Hz amplitude-modulated paradigm study

This study investigates the EEG activity of 48 participants in response to a set of four auditory stimuli: a pure tone (used as a reference), cicada song and cat's purr (natural sounds), and brownian noise (an artificial signal with a spectral content similar to that of certain natural sounds, such as water noise). In addition, a silent condition, corresponding to the absence of auditory stimulation, was included for subsequent analyses. The stimuli are amplitude-modulated by a 40 Hz sinusoid (modulation index = 1) and have a duration of 10 seconds. The experiment is conducted at two loudness levels (60 and 66 phons, diotic presentation), with 24 participants each. EEG acquisition is performed using a 24-channel mBrainTrain headset (international 10–20 system, passive electrodes, impedance maintained below 10 kΩ), coupled with a Smarting module, at a sampling rate of 500 Hz. The measurement consists in one session of two 10-minute runs (separated by a 5-minute break), each including 50 trials (10 repetitions per condition), spaced by intervals ranging from 6 to 10 seconds. Stimuli are presented in a pseudo-random order to avoid immediate repetitions of the same stimulus and to prevent a stimulus ending a sequence of five trials from starting the next sequence.