H2S concentrations and blank air were presented 40 times, and for any given block, stimuli were delivered to either the right or left nostril (4 blocks each in a counterbalanced order). Stimuli were presented in a pseudorandomized sequence based on Latin squares, with each of the four conditions occurring once within four consecutive trials. Before beginning the OERP test, participants were given four practice trials to ensure that they understood the task.
