Within an odorant block, four odorant stimulations were delivered in alternate order (e.g. Beer, Whiskey, Beer, Whiskey) with a 9 second stimulus onset asynchrony (SOA), during which subjects heard through noise dampening headphones, “Ready, Sniff, [Tone].” A computer-controlled odorant valve opened for a 2-second period to release the odorant at the “Sniff” command and closed at the tone, which signaled subjects to exhale. Subjects had been instructed to press 1 of 2 buttons on a response-box (Neurostim, Sterling, VA) after the tone to reflect their ability to detect the odorant (button 1 = yes, button 2 = no). This procedure served to help subjects focus on the task, and to verify compliance.
