J— PSYCHOLOGY 203 



ground or as a row of white fleurs-de-lys on a black background. Thus 

 we have a single stimulus pattern on the retina giving rise to two wholly 

 different perceptions. The after-image of a circle, moreover, will look 

 large or small as it is projected on to a far or a near object respectively, 

 although the area of retinal activity remains unchanged. And if a subject 

 seated below the object glass of a projection lantern looks at a picture 

 projected on to an inclined screen, he sees the picture as distorted although 

 it is easy to demonstrate that his retinal image is identical with that which 

 he would have received if the screen had been at right-angles to his line 

 of vision. 



Such facts as these are not easily reconcilable with the theory of simple 

 transmission of a retinal picture to the brain. That there is a close 

 relationship between the condition of physiological stimulation of the 

 retina and of the resulting pattern of visual perception is, of course, 

 obvious and is denied by nobody, but the relationship may not be of the 

 kind suggested by the analogy with telegraphic transmission. 



A better analogy for the modern view of perception is, I suggest, the 

 construction of one of the charts published with weather forecasts. The 

 lines of equal pressure on the charts are constructed from information 

 received from various land stations and ships, just as the perceptual 

 picture constructed by central activity depends on information received 

 from the sense organs. If no information as to barometric pressure is 

 received from a certain area, this does not mean that the corresponding 

 area must be left blank, but that the person constructing the chart must 

 fill it up by guess-work, which he generally does by constructing smooth 

 curves consistent with the other information. In the same way, in 

 Fuchs's experiments, it was found that central perceptual activity tended 

 to fill in areas from which no information was received from the retina 

 by simple completions providing ' good continuation ' with the figure 

 received on the rest of the retina. 



This view of visual perception may be expressed in various ways. We 

 may follow the Gestalt psychologists in speaking of perception as being 

 due to the combined effect of ' external forces ' belonging to the pattern 

 of retinal stimulation and of ' internal forces ' belonging to the central 

 factor in perception. Or we may speak of the processes of retinal stimu- 

 lation as ' cues ' for the resulting perception. These are different ways 

 of expressing the same fact that perception is regarded as a central activity 

 of which sensory stimulation is generally a determining cause, but not a 

 necessary condition. 



The analogy of the construction of a weather chart suggests a possible 

 way of looking at the process of visual perception which is alternative to 

 the transmission theory and which, I think, gives a much better account 

 of the experimental facts. It regards the mind (or the brain acting to 

 some extent as a unitary whole) as active in perception, responding to 

 information given by the sense organs and not merely reproducing a 

 pattern of stimulation from the sense organs. 



We have shown that seen shape is a product not only of the shape of 

 retinal stimulation but also of the perceived inclination in space of the 

 object looked at. Other experiments (to be mentioned later) show that 



