Fig. 2.

Relationship between glomerular activity maps and perceptual responses. (A) Raw glomerular activity maps evoked by 2-hexanone (25 and 75 ppm) and methyl valerate (25 ppm) predict that 2-hexanone presented at 25 ppm should be perceived as more similar to methyl valerate (at 25 ppm) than to itself at 75 ppm. (B) In contrast, z score-normalized glomerular activity maps predict that 2-hexanone will be perceived as more similar to itself, irrespective of concentration, than to methyl valerate. (C) Results from a cross-habituation study demonstrate that these odorants are more perceptually similar to themselves across concentrations than they are to other odorants. After a baseline presentation of mineral oil solvent (MO) followed by four presentations of the habituating stimulus (n-pentanal or 2-hexanone at 25 ppm; H1–H4), rats responded to presentation of a novel odorant at 25 ppm (n-pentanol or methyl valerate, respectively) with a significantly greater novelty response than they did to presentation of the habituation odorant at a higher concentration (75 ppm; ∗, P < 0.01 in both cases). (D) For both odor pairs, perceptual dissimilarity (red) covaried with the dissimilarity in normalized (black) and not raw (blue) glomerular activity maps. Solid lines, 2-hexanone vs. methyl valerate; dashed lines, n-pentanal vs. n-pentanol.