FIGURE, or FORM (Lat. figura, from fin (fere, to fashion, to feign; with Gk. 01)76urtv, thinyanein, to touch, Skt. dill, to smear, Moth. deiyan, to knead, OM:. teie, Ger. Teig, Icel. deig, AS. dab, Eng. dough). PERCEP TION or. The spatial attribute extension (q.v.) is ascribed only to certain classes of sensations, the visual and tactual; spatial relations, on the contrary, are predicable of all sensations alike, since all are localizable. Form, or figure. as used in psychology, is defined (Kuelpe) as "the general term comprehending all the spatial char acteristies that can be attributively predicated of an impression." The perception of the figure of an objeet may then be regarded as the perception of a sum of extensions. and the problem: involved are limited in their application to those .sense departments to which extent may be assigned.
The cutaneous perception of figure has re ceived but little investigation. By allowing the judgment to be made in visual term:, and by working with the 'procedure with knowledge' (see PsYcuoeirrsrcs) Major was able to deter mine the limes of form at various parts of the skin. The forms, angles, open and filled circles, and filled triangles, were applied to the tip of the tongue, the lips, and the tip of the middle finf,*er, and were gradually increased in size until the observer cognized tlie form. The results showed that the open circle was most easily cog nized; and that the capacity of the surfaces for cognition of the forms was. in order of excellence, tip of tongue, tip of finger. lips. On the tip of the finger. the following liminal values were ob tained: Angle with sides 1.13 nun., open circle :3 mm. in diameter, filled circle 5 min. in diameter, filled equilateral triangle with sides 4.3 mm. in length. The largest stimuli used: angle 10 mm., open circle 11 nun., tilled circle 12 nun., and triangle 9 mm., were too small to be cognized on the forehead, cheek, ball of thumb, and volar side the wrist. This dependency of the form-limen upon the place stimulated is illustrated by the simple experiment of drawing a pair of dividers along the arm from the elbow to the finger-tips, or from the lobe of one ear to the lobe of the other, across the face. The objectively parallel lines seem to diverge toward the wrist, and as they pass the lips. The cutaneous linen for form is susceptible of marked decrease through prac tice, as is well shown in the ability of the blind to read by touch from raised letters or from raised points of varied number and arrangement.
The visual perception of figure may, like the perception of simple extension, be obtained by the resting eye in monocular vision, but for its full development binocular vision is essential. The visual perception of figure furthermore in volves not only the perception of surface, but the perception of depth, or the apprehension of extension in the third dimension. One prob
lem of the perception of surface consists in recon ciling the fact that the field of vision pre sents a continuous surface with the fact that the sensitive parts of the retina. the rods and cones, form a mosaic of discrete points separated by non-sensitive areas. (The diameter of a ret inal cone is estimated at 0.0015-0.0044 mm., and the distance from the centre of one cone to the centres of adjacent cones at 0.0040 mm.) While explanations have been made in terms of binocu lar vision, of eye-movement, and of our a priori bias toward continuity, Kuelpe asserts that there is no real problem here at all. See also BLIND SPOT.
Of special importance to the perception of the third dimension of figures are those optical phenomena known as the prevalence and rivalry of contours. When we observe the form of an object, the images which are cast upon the retinas of the two eyes differ slightly, owing to the difference in the position from which the two eyes view the object. If now these two images completely fused, the principal factor in the perception of depth would be removed; if, on the other hand, the two images remained obstinately disparate, it would be impossible to refer them to a single external object. It is the 'prevalence' and 'rivalry' of contours which "prevent the fusion of the two retina] images, and secure to a certain amount of independence" (Hering) although "the impressions of the two eyes always fuse to a single idea" (WillIll. The contour phe nomena are easily demonstrable with the aid of the stereoscope. If. e.g. the right eye be stimu lated by a uniform surface of white, and the left eye by a black letter A upon a white background, there is afforded a pure instance of the prevalence of emitour. The A is not made grayish, not washed over by the white of the right monocular field, but is seen in perfect clearness in the re sultant single field: its contour suppresses or prevails over the surface presented by the white field. If each retinal field contours. and thesc contours possess little congruence, the phe nomenon of 'rivalry of contours' is observed. Thus, if the letter IT were presented to the left eye, and \\' to the right, or a vertical Noel: band to the loft eye, and a horizontal black band to the right, there would be no fusion of the two images, nor would either image permanently pre vail over the other; but there will be a constant rivalry and alternation of the two fields.
The visual perception of form plays an ha. portant part in the production of what are known as the "elementary :esthetic feelings." (See _ESTHETICS, EXPERIMENTAL.) Filially, the per ception of figure is extremely subject to illusion; small angles are overestimated, the height of a square is overestimated, etc. (See article IL