Experimental physiology.

Edward Albert Sharpey-Schäfer

Date:: 1912

Credit: Experimental physiology. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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$Discrimination time—For the measurement of this the observed person places one finger over each lever. It is agreed beforehand that he is only to react to a stimulus received on the one side, not on the other. The experimenter may stimulate either. It will be found that the reaction time is lengthened by a certain interval, and this increase of reaction time is termed the discrimination time. Determine and record this. Volitional time.—Similar arrangements are made, but with the understa^nding that it is only the hand on the side which receives the stimulus which is to be used for the response. The reaction time is now found to be still more lengthened because the observed person has to make a double decision ; viz., to determine not only which of the two hands has been stimulated, but also which one he has to use in response to the signal. Variations of the above experiments can be made with the employment of different sounds and the exhibition of different colours, but the methods for re- cording the reaction times are essentially the same. For rapid and accurate work it is usual to employ a specially constructed clock which can register the time of a reaction to a fraction of a second. Exiitatioa of tae coriex cerebri.—A monkey, anaesthetised with ether, is used for this demonstration. A considerable portion of the skull cap is removed on one side by trephining the skull and enlarging the aperture by bone-forceps. The dura mater is then cut through below and reflected towards the middle Line, thus exposing the cerebral surface. A pair of blunt-pointed platinum electrodes, with their points 1 mm. apart, is connected with a du Bois key in the secondary circuit of an induction-coil (use the Helmholtz modification) and applied to various spots in the excitable region of the frontal lobe, the first temporal gyrus, and tlie occipital lobe, and the results .are noted. The monopolar method of stimulation may also be employed for these observations. In this case one electrode is a flat pad of wash leather wetted with strong salt solution, and the other [stimulating] electrode is a small spiral platinum wire with blunt point, which is apphed to the excitable areas of the cortex.$

Experimental physiology.

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