LOCALITY (Lat. loealitas, from loealis, re lating to place. from locus. place), PEacErrioN OF. If we are touched upon sonic part of the skin, we are conscious of a pressure. which is definitely localized. Similarly, the various objects in the field of vision possess a definite position. Again, we are able to describe the position of our limbs when they are entirely concealed from our view. In other words. pressure. color, and articular ( joint) sensations are interpreted not only as cutaneous and articular pressures and colors, but also as pressures and colors at a particular place; they are somehow 'localized' in objective space. The problem of the perception of locality consists in a determination of the accuracy of localization, and an explanation of the conditions of its operation.
The accuracy of cutaneous localization is de termined by touching the skin of the observer with a pencil. On the removal of the pencil, the observer endeavors. with closed eyes, to place his own pencil upon the stimulated spot. On the wrist. the average error of localization is from 5 to 10 mm. The accuracy of cutaneous localization within one and the same area (the 'linen of separation') is determined by the simultaneous application of two points upon the skin. (See EXTENSION; LIMEN.) The fineness
of the visual perception of locality is measured by the minimal visual extent. The 'movement Innen.' or the least noticeable difference in the position of a limb, depends upon the joint at which the movement takes place. The larger joints have, as a rule. smaller movement listens; the shoulder discriminates a difference in the position of the hand better than does the elbow; the hip is noticeably more sensitive than the ankle (.5° and I° respectively).
Auditory impressions are also localized; but, since sounds do not themselves possess the spatial attribute, extension (q.v.), our judgment of the direction whence they come is effected indirectly by a process of 'associative supplementing.' (See ASSOCIATION OF InEAs.) By experience, definite tactual and visual space positions become inti mately associated to definite corresponding inten sive differences in the auditory impressions of the two ears. For the perception of locality in the third dimension, see DISTANCE, or DEPTII.
Kucl pe. Outlines of Psychology, trans lated (New York, 1895) ; Lotze, Medizinische Psyehologie (Leipzig. 1852) Titehener, Out line of Psychology (New York, 1899) \Vundt, Physiologisehc l'sychologic (Leipzig. 1893).