PERCEPTION 



^35 



much as 4 mo.)- The resulting observations are a 

 severe test for any theory of perception. 



It is clear from Kohler's reports that motor read- 

 justment precedes 'perceptual' readjustment by days 

 or weeks. Both motor and perceptual reorganization 

 seem 'easier' with up-down than with right-left 

 reversals. There are large individual differences in 

 rate and extent of readjustment, and there may be 

 systematic differences with age. Motor readjustment 

 (especially to up-down reversals) goes quite far, 

 permitting subjects, after 2 weeks or more, to engage 

 in fencing, skiing or riding a bicycle in heavy traffic. 

 There still remain tendencies, however, to make 

 'false starts,' and these persist to the end of the ex- 

 perimental period. In the perceptual sphere, adap- 

 tation is peculiar (Kohler says 'unreasonable')) in 

 that there seem to be piecemeal readjustments 

 within the scene. With right-left reversing spectacles, 

 subjects may report at some stages that they 'see' 

 cars on the correct (right) side of the street and hear 

 the engine noises as emanating from the correct side, 

 yet the cars bear license plates in mirror writing. 

 With up-down reversing spectacles, subjects note, 

 with amazement, that snow falls steadily downward 

 past trees that are seen as upside down. There are 

 similar but reversed 'piecemeal' effects when the 

 nl.issrs arc removed. 



The aftereffects are particularly variable from 

 subject to subject. For instance, apparent tilts of the 

 scene, with every tilt of one's head, can last for 2 

 weeks following removal of right-left reversing spec- 

 tacles (that had been worn continuously for 24 davsi. 

 Another subject, after wearing the same spectacles 

 for 37 days, reached a stage of 'nearly correct per- 

 ception,' but complained of diplopia (including 

 monocular diplopia) for some time after the glasses 

 had been removed. 



PARTIAL SPATIAL REORGANIZATION DURING SHORT-TERM 



experiments. It will be apparent that in spite of 

 these detailed and sensitive reports, much remains 

 to be done to delineate conditions for adaptation and 

 to explore the curious aftereffects. In view of the 

 difficulties of the long-term experiments, there has 

 been renewed interest in analogous short-term 

 studies involving rearrangement or disarrangement 

 of perceptual inputs. Some improvement of eye-hand 

 coordination during the first hour of wearing prisms 

 (laterally displacing the view of targets and hand) 

 was noticed already by von Helmholtz (501). Wundt 

 (552) reported the gradual disappearance of dis- 

 tortions and displacements of contours (meta- 



morphopsiae) after an inflammatory process in his 

 own retina had been arrested; he compared this 

 apparent adaptation to the overcoming of 'diop- 

 trically induced metamorphopsiae,' i.e. the dis- 

 tortions imposed by prisms or imperfect lenses. The 

 prism effects were restudied by Gibson (151) who 

 observed that the colored fringes gradually dis- 

 appeared (to reappear, briefly, in reverse orientation 

 when the prisms were removed); the apparent 

 curvature of (objectively) straight lines also di- 

 minished, and on removal of the prisms, objectively 

 straight lines seemed curved slightly in the opposite 

 direction. Most important was Gibson's insight that 

 the prism acted merely as a means for producing 

 curved lines. The same effect could be obtained by 

 looking at a curved line with bare eyes for several 

 minutes, during this period, the line became (sub- 

 jectively) less curved, and this effect could be 

 measured by the amount to which, immediately 

 afterwards, an objectively straight line had to be 

 curved in order to appear straight. Analogous effects 

 cm be found on prolonged inspection of straight 

 lines deviating by some degrees from the objective 

 horizontal or vertical: their deviation diminishes on 

 prolonged inspection ( 1 ",-', [53, 158, 281, 388). 

 I'.Hccts of this sort, obtained in a particular region 

 of the visual field, are essentially restricted to that 

 region; if obtained on monocular inspection, the 

 ell eel 'transfers' to the other eye (281 ).-' 



A possible binocular analogue is the gradual 

 adaptation to aniseikonic spectacles which distort 

 one monocular view against tin- other in a particular 

 meridian (6, 77). Reduction in the various subjective 

 distortions of depth, distance and size (see above) 

 occurs at different rates in different observers and 

 remains fractional in relatively unstructured environ- 

 ments [e.g. in Ames' 'leaf room' which lacks the 

 usual vertical and horizontal lines (6)]. In normal 



-'These changes in spatial organization on prolonged 

 inspection of particular stimulus patterns are much smaller in 

 extent than the gradual 'righting' of a complex scene, e.g. a 

 room seen through a slanting mirror (9, 536) or of an actually 

 tilted room viewed from an adjustable tilting chair (10). When 

 viewing such a room which is actually tilted by 30 , many 

 subjects accept the room as upright, especially if their own 

 body, on the chair, is tilted 30° with or against the tilt of the 

 room. There are, however, large and fairly consistent individual 

 differences in the extent to which subjects are influenced by the 

 visual scene under these and similar conditions. Witkin, whose 

 interests have turned lately to these individual differences, 

 ascribes greater 'field dependence' in such tasks to female as 

 compared with male subjects, and to children as compared 

 with adults (5441. 



