Rabbit Neonates and Human Adults Perceive a Blending 6-Component Odor Mixture in a Comparable Manner

Abstract

Young and adult mammals are constantly exposed to chemically complex stimuli. The olfactory system allows for a dual processing of relevant information from the environment either as single odorants in mixtures (elemental perception) or as mixtures of odorants as a whole (configural perception). However, it seems that human adults have certain limits in elemental perception of odor mixtures, as suggested by their inability to identify each odorant in mixtures of more than 4 components. Here, we explored some of these limits by evaluating the perception of three 6-odorant mixtures in human adults and newborn rabbits. Using free-sorting tasks in humans, we investigated the configural or elemental perception of these mixtures, or of 5-component sub-mixtures, or of the 6-odorant mixtures with modified odorants' proportion. In rabbit pups, the perception of the same mixtures was evaluated by measuring the orocephalic sucking response to the mixtures or their components after conditioning to one of these stimuli. The results revealed that one mixture, previously shown to carry the specific odor of red cordial in humans, was indeed configurally processed in humans and in rabbits while the two other 6-component mixtures were not. Moreover, in both species, such configural perception was specific not only to the 6 odorants included in the mixture but also to their respective proportion. Interestingly, rabbit neonates also responded to each odorant after conditioning to the red cordial mixture, which demonstrates their ability to perceive elements in addition to configuration in this complex mixture. Taken together, the results provide new insights related to the processing of relatively complex odor mixtures in mammals and the inter-species conservation of certain perceptual mechanisms; the results also revealed some differences in the expression of these capacities between species putatively linked to developmental and ecological constraints.

Experience shapes our odor perception but depends on the initial perceptual processing of the stimulus

“…Another blending mixture, RC (six components, smelling like red cordial, also named grenadine; Le Berre et al, 2008;Sinding et al, 2013) was used as a control stimulus during testing but not during the preexposure sessions.…”

“…Indeed, to be rated as more configural, the AB mixture should have obtained a typicality score greater than 8 (maximum median value observed here, 10 being the possible maximum value), which is unlikely. This methodological issue might be overcome by using complementary methods, such as a similarity test or a free-sorting task (see Sinding et al, 2013, for tests of a sixcomponent mixture). A free-sorting task would allow for assessing the similarity between the mixture and its components, and we could expect that the group preexposed to the mixture would consider the mixture more distant perceptually from its components than control groups would.…”

Configural processing of odor mixture: Does the learning of elements prevent the perception of configuration in the newborn rabbit?

“…In Experiment 3, we also used the RC mod mixture, which was composed of the 6 odorants included in RC but in different proportions (5/4.3/2.8/41.8/4.3/41.8%, respectively for V/F/IA/B/EA/D). At these proportions, RC mod is elementally processed by newborn rabbits [17].…”

“…The components of the RC and RC mod mixtures and of the submixtures tested here induce no spontaneous sucking response in pups [17,18]; they were therefore considered neutral stimuli before conditioning.…”

“…Rabbit pups indeed perceive the 6-component Red Cordial (RC) odor mixture in the weak configural way. As for AB, the conditioning to the mixture induces responsiveness to the odorants, but conditioning to one element does not promote responsiveness to the mixture [17]. Moreover, pups do not respond to RC after conditioning to 2 or 3 RC odorants, but they do after conditioning to RC submixtures of 4 or 5 elements [18].…”