Discrimination Results. Mean (± SEM) digging times for unilaterally bulb-x mice during 60 sec discrimination trials comparing two sand-filled dishes containing either S+ or S- odors. Data in the left column (controls) are from three of four trained adult mice that had normal nares. Data in the right column (occluded) are from three of four trained adult mice that had a naris occluded on the first postnatal day positioned contralateral to their subsequent adult bulb-x. Mice were tested on their ability to discriminate the S- and increasingly diluted S+ in S- stock (see methods). Filled arrows designate threshold as determined by lowest dilution (just left of arrow) at which the mouse showed significant discrimination by Mann-Whitney test (p < 0.05) in a six trial block. Note that a mouse had to fail to discriminate a given dilution on two consecutive days to establish threshold. In the case of Mouse S (lower right panel), after threshold was determined its formerly occluded naris was opened surgically (open arrow). The traces in the inset are recordings from a thermistor probe placed just inside the external nares after naris opening. These traces establish that respiration was restored through the surgically reopened naris. After a two-day recovery period following naris reopening, Mouse S again failed to discriminate the dilution (0.08% S+ stock in S- stock) it had previously failed on during threshold testing.