Measurement of Olfactory Threshold in Normal Korean Adults with Combined Use of Bounded CCCRC Test and Step Method

The high variability of measured olfactory thresholds in humans reflects very broad range of sensitivity within and among individuals. This can be derived from the strongly compressive nature of olfaction, which makes it relatively hard to compare the size of two stimuli in odor sensation. However, we know that some portion of the variation is the result of extrinsic factors e.g. the method used to measure the olfactory threshold. For this reason, in order to address the bias and reliability of a psycophysical method, we combined the use of the CCCRC (Connecticut Chemosensory Clinical Research Center) test with the step method in 40 normal Korean adults twice a week for the evaluation of threshold. The measured thresholds showed high test-retest reliability and the threshold estimates remained consistent during the testing without trial-biases. Based on the results, we can conclude that a combined test using the CCCRC test and step method can be used in the measurement of olfactory threshold in a clinical context.

Comparison of Olfactory Threshold Tests:CCCRC Test versus Step Method / 대한이비인후과학회지

There are many variables that can be manipulated in the study of olfactory thresholds. They include the choice of odorant, the way to bring the stimulus to the subject's nose, number of trials, interval between trials, dilution method, environmental conditions, as well as psychophysical method. The focus of this study lay on how much differences were made by the psychophysical method, the sequence of presentations of stimuli that led to calculation of an index of sensitivity and how reliable the result of step method in olfactory threshold testing is. The olfactory threshold tests entailed comparison of procedures: 1) a procedure of two-alternative forced-choice(2AFC) testing by an ascending method of limits(CCCRC test), 2) a two-alternative forced-choice(2AFC) version of step method that used a computerized algorithm to calculate threshold on an ongoing basis throughout testing. As a result, mean concentration difference of 7.6-fold was achieved in the thresholds by the two procedures and inter-test correlation coefficient was 0.46. Estimation of threshold in the step method remained relatively constant after 10 trials to the end of the 30 test-trials without biases, which meant step method showed coherent data. Accordingly step method is suitable for olfactory threshold test despite of relatively long testing time.