The effects of variation of intertrial interval on exploration of elevatd and enclosed mazes

The interval between exploratory trials was varied in experiments using simple elevated or enclosed mazes. Activity on the second trial was depressed for short intertrial intervals but had recovered after about 10 min.; the degree of recovery was different in the two types of maze. A second decrease in second trial activity was found with inter-trial intervals of more than 20 min., but a further experiment suggested this was due to the effects of delay itself, rather than to previous experience of the environment.     

The use of extreme groups to test for the presence of a relationship

Experimenters in psychology frequently investigate the relationship between two variables by selecting extreme groups on the first measure and comparing their mean scores on the second. This paper considers the efficacy of this procedure from the criterion of the power of the statistical tests. Optimal cutting points for the extreme groups are defined, and the power of the difference approach is compared to that of significance tests for the productmoment correlation coefficient.     

Shorter articles and notes two more visual theorems

The basis of the widely held opinion that the spectral sensitivities of the mechanisms determining trichromacy must be linearly related to the spectral mixture functions is examined, and a proof from simple assumptions is stated.

It is proved also that, on the van der Velden hypothesis of independent sensitive units, a spatial or temporal summation law of the form AIⁿ = c implies a frequency-of-seeing curve of the form Q = I—e^-KIn (Q = probability of detecting a stimulus of size A and intensity I; n, c and K are constants).