Six CD-1 mice were used in this study to determine the olfactory detection thresholds for "green" odors using an automated olfacatometer.An operant chamber was connected to the olfactometer via a sampling port in which the odorants were presented. When inserting the nose into the sampling port (making a nose poke) the mouse breaks a photo beam triggering the 2 s presentation of either an odorant used as the rewarded stimulus (S+) or a different odorant used as the unrewarded stimulus (S–). A correct response to the S+ consists of licking at a waterspout in the sampling port, water reinforcement is presented by the opening of a reinforcement valve for 0.04 s presenting a water droplet of 2.6 µl through the waterspout. For an incorrect response (licking the waterspout in response to the presentation of the S-) no water reinforcement is presented.  

For all the critical tests, five to seven blocks (depending on the time taken by the individuals to complete the blocks) of 20 trials each using a given stimulus pair were conducted per animal and day. Each block consisted of 10 S+ and 10 S- presentations in pseudo randomized order.  “Green” odors with different concentrations were used as S+ and near-odorless diethyl phthalate was used as the S- in all critical tests. Starting with a gas phase concentration of 1 ppm, each S+ was presented in 10-fold dilution steps for a total of 40 trials until an animal failed to significantly discriminate the odorant from the solvent (diethyl phthalate). Subsequently, an intermediate concentration (0.5 log units between the lowest concentration that was detected above chance and the first concentration that was not) was tested in order to determine the threshold value more exactly.