BILATERAL DETECTION THRESHOLDS IN DEXTRALS AND SINISTRALS REFLECT THEMORE SENSITIVE SIDE OF THE NOSE, WHICH IS NOT LATERALIZED

Several fundamental questions remain enigmatic concerning human olfact ory sensitivity, including (i) whether detection threshold differences exist between the two sides of the nose (and, if so, whether such dif ferences are influenced by handedness) and (ii) whether bilateral (i.e . binasal) stimulation leads to lower thresholds than unilateral stimu lation (and, if so, whether the degree of facilitation is inversely re lated to general olfactory ability). In this study, a reliable and wel l-validated single staircase procedure was used to establish bilateral and unilateral detection thresholds for the cranial nerve I stimulant phenyl ethyl alcohol in 130 right- and 33 left-handed subjects. No di fferences in sensitivity between the left and right sides of the nose were observed in either group. Bilateral thresholds were lower, on ave rage, than unilateral thresholds when the latter were categorized in t erms of left and right nares. However, the bilateral thresholds did no t differ significantly from those of the side of the nose with the low er threshold. Overall smell ability, as measured by the University of Pennsylvania Smell identification Test, did not interact with any of t he rest measures. These data imply that (i) the left and right sides o f the nose do not systematically differ in detection threshold sensiti vity for either dextrals or sinistrals and (ii) if central integration of left:right olfactory threshold sensitivity occurs, its effects do not exceed the function of the better side of the nose.