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Odor sampling and
Odor discrimination
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Iversen, I.H. (2008).
An inexpensive and automated method for presenting olfactory or
tactile stimuli to rats in a two-choice discrimination task.
Journal of the Experimental Analysis of Behavior, 90, 113-124.
An inexpensive and automated method for presentation of olfactory
or tactile stimuli in a two-choice task for rats was implemented with the use
of a computer-controlled bidirectional motor. The motor rotated a disk
that presented two stimuli of different texture for tactile
discrimination, or different odor for olfactory discrimination.
Because the solid olfactory stimuli were placed outside the chamber
in metal pods with a mesh at front for odor sampling, “washout”
of odors between trials was not necessary. To avoid differential auditory
cues from motor rotation, the stimuli were arranged such that on each trial
the motor always rotated exactly one quarter revolution (in 1s), left
or right, to present the next stimulus at trial start. To illustrate the use
of the equipment, 2 rats were trained on tactile discrimination and 2 rats on
olfactory discrimination. The rats sampled the stimulus on the disk through
a port on the back wall by sniffing at it (olfactory) or touching
it (tactile). The task was a go-left/go-right discrimination with
the stimulus on the disk being discriminative for which lever provided
reinforcement. The rats reached a stable level above 90% correct after 21
and 32 training sessions for tactile and olfactory discrimination, respectively.
The article outlines how the equipment was constructed from low-cost components.
Inputs from and outputs to the equipment were implemented through the parallel
port of a personal computer without the use of a commercial interface board.
The method of automated and low-cost presentation of olfactory or tactile stimuli
should be of use for a variety of experimental situations such as matching-to-sample
and cross-modal discrimination.
Key words: olfactory discrimination, tactile discrimination, two-choice task, automated stimulus presentation, bidirectional motor, rats