PERCEPTION 1609 



is no adequate quantitative comparison of the mo- 

 nocular with the binocular conditions. 9 



Possibly a variant of this procedure is the wipe-out 

 phenomenon which results when an information- 

 bearing visual stimulus (e.g. a triangle) is flashed 

 tachistoscopically, and followed within critical time 

 by a white flash, with appropriate time-relation. The 

 first (figured) flash cannot be reported; it has been 

 'wiped out' by the bright field which followed (324). 

 Unfortunately, this effect seems to appear only if 

 both exposures are given to the same eye; it is thus 

 possible that the second (unfigured) flash serves 

 merely to obliterate an afterimage that would nor- 

 mally appear and assist in the perception of the 

 briefly exposed pattern. 



Ontogenetic Considerations 



Our knowledge of shape perception in children is 

 surprisingly scant, and a good deal of the work is 

 contradictory. It has been asserted that children shovt 

 the effect of the 'laws' of grouping more than adults; 

 or, differently put, that they can overcome these ef- 

 fects less (e.g. by selective attention to detail, set or 

 instructions). Thus, hidden figures (like those illus- 

 trated in fig. 14) are difficult to unscramble for chil- 

 dren; in fact, most of the patterns developed by 

 Gottschaldt (164, 165) present insoluble perceptual 

 tasks for children below the age of six, according to 

 Witkin (542) and Ghent (148). There also are marked 

 individual differences in the performance of adults in 

 this respect (542). As Ghent (148) has pointed out, 

 the crucial source of difficulty may be the sharing of 

 contours; the young child is disproportionately handi- 

 capped whenever the contours of the embedded 

 figure also form integral contours of the embedding 

 configuration. By contrast, the partial concealment ol 

 figures by intersecting lines ("mixed figures') presents 

 less difficulty to normal children (fig. 7). 



According to Stern (447, 448), children below the 

 age of six are less disturbed than adults in recognizing 

 patterns shown to them in unusual orientation (<■ g. 

 upside down). Such an observation would weigh 



9 The phenomenon gains in interest in view of recent dem- 

 onstrations that resolution of successive light flashes at cat 

 or monkey optic cortex (where it is measured by discrete 

 evoked potentials) can be improved by intercurrent electrical 

 stimulation of the midbrain reticular formation 1 3^4 1. Micro- 

 electrode recordings for individual neurons of the optic cortex 

 of the cat have revealed a similar effect, trains of light flashes 

 are followed by discrete neural discharges at higher than normal 

 rates if reticular formation or nonspecific thalamic nuclei are 

 intercurrently stimulated (245)- 



FIG. 7. "Mixed figures' employed in testing normal child- 

 ren and those with brain injury. Bach of the nine composite 

 drawings was presented individually and without the num- 

 bers shown See Teuhei (t)-, illustrated subsequently in 

 Ghent 1 148).] 



against the virus n| Hebb 1188), since it would imply 

 greater rather than less transposability of shape at 

 younger ages. Actually, the evidence is unclear. 

 Children who cannot read often look at drawings in 

 picture books which they hold upside down; their 

 own drawings may show orientations on the page 

 which are peculiar From the adult standpoint (5771. 

 Yet more recent studies (22g, 230; Ghent, unpub- 

 lished observations) indicate that children may have 

 more (not less) trouble than adults in identifying in- 

 serted pictures. Their preference for holding picture 

 books in peculiar ways may be related to consistent 

 positional preferences which they exhibit just as 

 strongly when presented with unfamiliar geometric 

 patterns. 



A weakness of many of the available studies of child 

 perception is their failure to employ converging opera- 

 tions. The indices of a particular perception are often 

 drawings made by the children [cf. Eng (113), 

 Yolkelt (493) and Osterrieth (372)], which preclude 

 decision as to whether the peculiarities lie in the 

 child's perceiving, in his drawings, or in both. Less 

 ambiguous results can be expected from systematic 

 application of identical methods for the study of form 

 perception in children and in nonverbalizing sub- 



