Effects of Environmental Variables

Abstract

During the early 1950s systematic investigations of the open-field as a dependent measure of activity were begun. One of the main variables studied has been illumination of the open-field. In addition to illumination, the author has shown that the dimensions of the open-field can influence activity levels, in fact the dimensions can cause a reversal in the traditional orderings of activity (Whitford & Zipf, 1975). This paper explored the effects of dimension of the field and illumination level on open-field activity of pure strain mice. Twenty studies were randomly sampled from a review article by Sprott and Staats (1975), with the constraint that the studies deal with open-field activity. The dimensions of the open.fields sampled varied greatly, for example, McClearn (1959) used a 30- x 30-in. field with 36-in. sides, while Blizard (1971) used a circular field. In this sample none of the open-fields had the same dimensions. In view of the strain rank-order reversals reporred earlier (Whitford & Zipf, 1975) this is a serious problem. It has been demonstrated by many investigators that illumination levels affect activity in the open-field. The illumination levels reported in this sample varied from 0 ft-c, to 480 ft-c., with only six studies reporting any illumination levels. In a recent study by the author albino mice were differentially affected by various levels of illumination, with the greatest activity under intermediate illumination levels, not the lowest levels (Whitford & Zipf, 1974). In a second study in which pigmented and albino strains were allowed to select their own illumination levels (10 ft-c., 30 ft-c. or 165 ft-c.) neither albino nor pigmented strains chose the lowest illumination levels, as might be expected (Zipf & Whitford, 1975). It seems clear that, if conclusions currently being drawn concerning open-field activity are to be valid and the results both comparable and replicable, authors should report accurately all measurable variables, such as size. illumination and ceiling height of the open-field. The time to investigate and control for these environmental variables has long since passed. It is quite clear that the results of an open-field experiment can be reversed by simply changing one environmental variable (Whitford & Zipf, 1975). In view of the magnitude of the implications being drawn from open-field studies, many previous studies should be re-evaluated and without systematic control of these environmental variables the conclusions drawn from the increasing number of studies utilizing the openfield should be seriously questioned.