Newborn Rabbit Perception of 6-Odorant Mixtures Depends on Configural Processing and Number of Familiar Elements

Abstract

Perception of odors, i.e. usually of mixtures of odorants, is elemental (the odorants' odor qualities are perceived in the mixture) or configural (the odor quality of the mixture differs from the one of each odorant). In human adults, the Red Cordial (RC) mixture is a configurally-processed, 6-odorant mixture. It evokes a red cordial odor quality while none of the elements carries that odor. Interestingly, in newborn rabbits, the same RC mixture is weak configurally perceived: the newborns behaviorally respond to all the elements after conditioning to the whole mixture, but not to the mixture after conditioning to a single element. Thus, they perceive in the RC mixture both the odor quality of the RC configuration and the quality of each element. Here, we aimed to determine whether this perception is modulated by quantitative (number of elements) and/or qualitative bits of information (nature of elements) previously learned by the animals. Newborns were conditioned to RC sub-mixtures of different complexity and composition before behavioral testing to RC. Pups generalized their sucking-related response to RC after learning at least 4 odorants. In contrast, after conditioning to sub-mixtures of another 6-odorant mixture, the elementally perceived MV mixture, pups responded to MV after learning one or two odorants. The different generalization to RC and MV mixtures after learning some of their elements is discussed according to three hypotheses: i) the configural perception of RC sub-mixtures, ii) the ratio of familiar/unfamiliar individual information elementally and configurally perceived, iii) the perception of RC becoming purely elemental. The results allow the first hypothesis to be dismissed, while further experiments are required to distinguish between the remaining two.

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

“…Specifically, is the perception of a configuration permanent in a mixture, or is it modulated by experience and early exposure to the mixture components? The previous results did not allow us to draw definitive conclusions on this question; therefore, two concurrent hypotheses have been suggested [18]:…”

“…The [17,18]. 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).…”

“…Then, the single odorant concentrations were the same as the concentrations of each odorant in the mixture. Previous analyses showed that the concentration of odorants or their respective vapor pressures are not involved in pups' responsiveness and that the stimuli are considered iso-intense by humans [18].…”

“…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]. Such responsiveness to the whole mixture after conditioning to a sufficient number of its elements raises the question of odor mixture processing in animals, a critical skill for the representation of their chemosensory world.…”

“…Then, we tested the hypothesis of the perceptual disappearance of the RC configuration through a single conditioning trial to sub-mixtures of 4 or 5 RC elements 24 h before the repeated conditionings to RC (Experiment 2). As conditioning to elemental sub-mixtures is equivalent to simultaneous conditioning to the distinct elements that compose the sub-mixture (i.e., the pups later respond to each element [18]), we suspected that after learning more than 50% of the RC elements, pups would not perceive the RC configuration in the whole mixture anymore. Finally, to examine the same hypothesis while taking into account that the single early conditioning to an elemental sub-mixture could be altered by the subsequent repeated conditionings to the mixture, pups were daily conditioned to both the sub-mixture and whole RC mixture for three days (Experiment 3).…”