An experiment was designed to establish optimum conditions for using Hall's open-field test of emotionality in white rat. A large (N = 192) factorial design permitted simultaneous evaluation of following components of test which were thought to be productive of emotional responses: size of test arena, intensity of illumination and intensity of sound. effects of pre-trial shock, food deprivation and sex difference were also investigated. Other variables were strictly controlled.

results, principally analysed in terms of defecation and ambulation scores, show that females defecate significantly less than males and ambulate more, that noise is a potent factor in evoking emotional elimination and light less so. Arena size does not affect defecation, but rats run farther in a larger arena. Pre-trial shock reduces defecation, whereas food deprivation has no significant effect. Interactions are few, and mostly concern sex differences in response.

It is concluded that test can yield sensitive indicators of an emotional response, and that this response is susceptible, within limits, to experimental control. implications for use of test are discussed.