Olfactory adaptation consists of both cortical and peripheral components. Since there was no significant effect of adapting side [F (1, 11) = 0.40, p = 0.54], adapting odorant [F (1, 11) = 0.55, p = 0.47], testing side [F (1, 11) = 0.004, p = 0.95], or testing odorant [F (1, 11) = 0.27, p = 0.61], the 16 combinations of adapting side, adapting odorant, testing side, and testing odorant (see Supplemental Experimental Procedures for details) are collapsed into four categories: same nostril same odorant, same nostril different odorant, different nostril same odorant, and different nostril different odorant. Same or different is with respect to the adapting nostril and adapting odorant; e. g. ‘same nostril same odorant’ means the same nostril that had been pre-adapted to an odorant (PEA/n-butanol) was presented with the same odorant (PEA/n-butanol). The y-axis depicts the difference in the intensity ratings obtained after and before the adaptation on a 100-unit visual analogue scale. Error bars represent standard errors of the mean. The asterisks indicate significant difference from zero or between conditions, p < 0.05.

Binaral rivalry. (A) All twelve subjects tested experienced switches between perceiving predominantly ‘rose’ and predominantly ‘marker’ (y-axis, similarity rating to ‘rose’ or ‘marker’ on a 100-unit visual analogue scale as shown in Figure 1B) over 20 intermittent samplings (x-axis) of PEA and n-butanol, one presented to each nostril. Dots above the middle line indicate an olfactory percept of predominantly ‘rose’. Dots below the middle line indicate an olfactory percept of predominantly ‘marker’. (B) Illustration of the visual analogue scale used for olfactory similarity ratings. (C) Histogram of the mean similarity ratings across the 20 samplings from the 12 subjects. How biased one was towards perceiving ‘rose’ or ‘marker’, as reflected by his/her mean similarity rating, follows a normal distribution with the mean at 53.9% similar to ‘marker’. (D) Histogram of the similarity ratings (240 ratings from 12 subjects, each with 20 samplings). The distribution can be modeled with the sum of two normal distributions (dotted curve): , where h₁, μ₁, σ₁ are the height, mean, and standard deviation, respectively, of the first normal distribution, and h₂, μ₂, σ₂ are the height, mean, and standard deviation, respectively, of the second normal distribution. Here μ₁ corresponds to 66% similar to ‘marker’, and μ₂ corresponds to 65% similar to ‘rose’.

Mononaral rivalry. Ten out of the twelve subjects tested experienced switches between perceiving predominantly ‘rose’ and predominantly ‘marker’ (y-axis, similarity rating to ‘rose’ or ‘marker’ on a 100-unit visual analogue scale) over 20 intermittent samplings (x-axis) of a 1:1 mixture of PEA and n-butanol. Dots above the middle line indicate an olfactory percept of predominantly ‘rose’. Dots below the middle line indicate an olfactory percept of predominantly ‘marker’.