272 



SCIENCE 



[N. S. Vol. XXVII. No. 685 



liberated after showing them to curious 

 friends. 



J. Stanford Brown 



SPECIAL ARTICLES 



RIGHT-HANDEDNESS AND PERIPflERAL VISION 



Op- right-handedness, three facts seem to be 

 fairly well established: it is hereditary, it 'de- 

 velops by a method of trial and error in the 

 seventh month of life, it is due to some as yet 

 unknown ascendency of the left hemisphere of 

 the brain. That it is inheritable points to 

 its origin as a congenital variation. That it 

 develops in the seventh month of life points 

 to its dependence upon the ripening of some 

 bodily structure. The precise manner in 

 which it is dependent upon the left hemisphere 

 has never been satisfactorily explained. In 

 fact, the very pertinent question whether the 

 ascendency of the left hemisphere rests in the 

 sensory or motor areas has, seemingly, never 

 been raised. Reflection will show that the ini- 

 tial difference must be sensory and not motor. 

 If the reflex act concept of the manner of 

 working of the nervous system is correct, and 

 if, as a consequence of that concept, currents 

 of innervation flow only from afferent to effer- 

 ent neurones, always in the " forward direc- 

 tion," it follows that the ascendency of the 

 left hemisphere must, in the first instance, 

 exist in the sensory neurones. For, the con- 

 traction of muscles of the right arm is merely 

 a consequence of the discharge of nerve cells 

 in the left motor cortex. But, the discharge of 

 these cells is, again, a consequence, merely, 

 of the discharge of sensory cells which are 

 situated either in the sensory cortex or, pos- 

 sibly, in the periphery. If this reasoning is 

 sound, ■ it follows that where there is motor 

 bilateral asymmetry there must first be sen- 

 sory bilateral asymmetry. 



Experiments' carried out during the past 

 year, on the comparative sizes of objects which 

 are seen in indirect vision, brought to light the 

 fa;ct that a marked difference in the percep- 

 tion of size exists between the right and left 

 halves of the retinae of the two eyes. The 



' For a full rejiort on these experiments, see a 

 forthcoming article in The Psychological Review. 



experiments were made with a perimeter. The 

 objects compared were the orbits described by 

 two black spots which were borne upon the 

 peripheries of two slowly moving white card- 

 board discs. The spots were attached to 

 movable -radii so that the orbit of the appar- 

 ently larger disc could be reduced until it 

 equaled, subjectively, the orbit of the smaller. 

 In this way, quantitative measurements were 

 made for four meridians, vertical, horizontal 

 and two oblique, and for three parallels of 

 latitude, 10°, 20° and 25°, of the visual field. 

 The observations were either (a) peripheral 

 comparisons, in which the discs were situated 

 in the periphery of the field of vision, upon 

 some one of the four meridians, on opposite 

 sides of the fixation point or (5) foveal-periph- 

 eral comparisons, in which one disc covered 

 the fixation point and the other occupied some 

 position in the periphery. The results of both 

 (a) and (h) follow, (i.) The discs on the 

 upper vertical, right-upper oblique, right hori- 

 zontal and right-lower obliqiie meridians ap- 

 pear larger than similar discs symmetrically 

 placed on opposite sides of the fixation point 

 or at the fixation point, (ii.) This result is 

 constant for hoth eyes, (iii.) The enlarge- 

 ment is greatest at 25° from the fixation point 

 and least at 10°. (iv.) The enlargement is 

 gTcater in the right-upper field than in the 

 right-lower field. When it was seen that ob- 

 jects in the right half of the field of vision are 

 imaged upon the left corresponding halves of 

 the retinsB and that these halves of the com- 

 bined eye are connected with the left occipital 

 hemisphere, it was suggested that the illusion 

 of size might be reversed with left-handed 

 persons, who are, presumably, right-hemi- 

 sphered. To test this point, crude observations 

 were made with small clay discs and larger 

 cardboard discs, placed upon a table, about 12 

 cm. apart, in front of the observer. The ob- 

 server looked with one eye at a time, from a 

 height of about 75 cm., at the middle point 

 between the discs and compared, in indirect 

 vision, their size. 183 observations were made. 

 To 100 persons, the right disc appeared larger 

 to both eyes. To 45 persons, the left disc ap- 

 peared larger to both eyes. These results, as 

 unequivocal, are the only ones that need be 



