For the recording of detection performance, stimulus ratings, and EEG activity, the chemosensory stimuli were presented according to the method described by Kobal [28], using a constant flow, six channel olfactometer (OM6b, Burghart Messtechnik GmbH, Wedel, Germany). Both nostrils were stimulated simultaneously, and accordingly, both air streams (100 ml/s each) were controlled by separate mass flow meters. In the olfactometer, the glass tubes containing the stimuli were stored in a warm-water chamber, and the stimuli were delivered (duration = 0.5 s) to the participants through a teflon tube. The temperature of the gas flow at the exit of the olfactometer was 37°C and the relative humidity was set above 80%. White noise of 80 dB (A) was presented binaurally over earplugs (Etymotic Research, ER3-14A), in order to prevent the participants from hearing the switching valves of the olfactometer.
