Abstract: In studying behaviour supposedly motivated by fear or by exploration, consideration should be given to the biological functions of these two systems and to the ways in which the experimental environment may affect the performance of ‘natural’ responses. Extreme caution is needed in comparing the effectiveness of different stimuli and the amounts of fear or exploration represented by different responses. In particular, it should never be assumed when making such comparisons that the relative intensities of different stimuli and responses are constant.
