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PHYSIOLOGICAL FACTORS OF THE ATTENTION-PROCESS. 299 attract attention to itself is a fact that has not escaped the notice of psychologists. Thus Dr. Stout writes: "Dead silence and monotony of colour in the environment are in my own case very unfavourable conditions [for mental work]. The sound of running water, a well-lighted room, a variety of objects in it, an open window with a pleasing prospect are very favourable conditions, even though I take no notice of them." 1 And the favourable effect of gentle muscular exercise, such as walking, has been frequently remarked. But the most valuable evidence in support of the view I am suggesting is afforded by certain experiments made by Dr. C. Fere. In an article in the Revue Philosophique 2 he reports experiments which prove that the energy of a movement of reaction to a sensory stimulus of given strength is considerably increased by the simultaneous stimulation of other sense organs, e.g., a reaction to a touch-stimulus may be made more energetic, and the time of the reaction may be shortened, by allowing light to fall on the retinae, and " con- versely, the taking away of all light determines in perfectly normal subjects a prolongation of the time of reaction, which may exceed one-fourth or even one-third of the normal time." And he shows that similar effects can be produced by heat, sound and electrical stimuli. Fere shows also that a general state of tension of all the muscles of the body favours rapid and energetic movement of any one set of muscles, that, e.g., the time of a certain reaction is shorter when the subject stands than when he reclines during the experiment. In his book Sensation et Mouvement' 3 Fere reports other observations which bear out this view. He shows (p. 7) that the converse of the above statements is true, that not only is a state of general muscular tension favourable to mental activity, but mental activity is favourable to muscular work, that the force of a maximal voluntary contraction measured by the dynamometer may be increased by as much as 25 per cent, through immediately preceding intellectual activity. On comparing the maximal muscular efforts that persons of different classes are capable of putting forth, he finds that persons accustomed to intellectual work can produce momentary contractions of greater force than can be produced by manual labourers, and he sums up the result of -his observations of this kind in the statement that " the force of the maximal momentary contraction varies with the 1 Analytic Psychology, vol. i., p. 172. 2 Oct., 1890. 3 Paris, 1900.