Studies in Olfactory Acuity. I: Measurement of Olfactory Thresholds in the Rat

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Abstract
The capacity of the rat to respond to olfactory cues has been studied in three experimental situations: (i) an elevated Y-maze, (ii) a rectangular choice apparatus in which extraneous environmental cues were present, and (iii) a circular choice apparatus from which such cues were either excluded or randomized. No rat showed any sign of learning on the Y-maze even after extensive training and the application of electric shock as deterrent for error. Some rats succeeded in performing an olfactory discrimination in the rectangular choice apparatus but learning was retarded, and in some cases inhibited, by the counter-influence of non-olfactory factors. All rats readily learned an identical discrimination when shielded from such cues in the circular choice apparatus which provides a satisfactory medium both for training and for the study of olfactory acuity. Differences in the behaviour of rats on these three types of apparatus suggest first, that the formation of learned habits based on olfaction depends on the close contiguity of stimulus and reward, and second that the sense of smell possesses weak orientating properties by comparison with those exerted by other modalities. The findings thus help to explain differences in the ease or difficulty uith which olfactory discriminations have been established by earlier workers.