Page:Philosophical Review Volume 3.djvu/245

] changes caused by the approach of an object. Observers blindfolded could distinguish changes in the character of a screen placed before the face. When the face was covered and the ears left open, this ability was not diminished. When the ears were stopped and the face exposed, this ability was entirely lost. Introspection on the part of the observers indicates that the judgments were based upon changes in the character of sounds from beyond the screen.

Exner was led to believe that the reaction time was 10σ longer when the stimulus was applied to the reacting hand than when applied to the other. Some 500 experiments made in the psychological laboratory at Clark University show that the reaction time is practically the same, whether the stimulus is applied to one hand or the other.

The experiments consisted in sorting a pack of different kinds of cards, as indicated by a word or a picture, into piles of the different kinds. After the cards had once been sorted with the piles in a certain order, a longer time was required to sort them with a different arrangement of the piles. This interference from the previously formed associations decreased rapidly during the first eight seconds, afterwards more slowly, vanishing entirely in less than twenty-four hours.

The method consists in a classification of artificial stars into groups separated from each other by equal magnitudes. The changes in the magnitudes of the stars were made by means of an episkotister increasing in darkening value from circumference to centre. The