414 SECTIONAL TRANSACTIONS.— J. 



If these facts are so, then, in virtue of the rule of pathology we may say 

 that : 



(a) The function destroyed is in some way connected with the normal 



activity of the cerebrum, 

 (i) The function destroyed is not the power to receive sensations, nor 



the power to interpret the data of sense. 



There remains, therefore, a mental function intermediate between the 

 power to become aware of sensory qualities and the power to interpret the 

 data of sense. This intermediate function is here termed the synthetic 

 seme. 



III. The Theory of Perceptions. 



The synthetic sense is a complex group of functions. Thus the ability 

 to synthesise tactual data may be destroyed while the power to synthesise 

 other sensory data may remain intact. 



The process of synthesis is to a large extent dependent on past experience, 

 but experimental data show that the revival of the images of past experience 

 is not an essential element of the synthesis. 



But what Gestalt psychology recognises as differentiation between figure 

 and background is one of the elements in the process of synthesis. This 

 differentiation is not interpretation, but a necessary condition that inter- 

 pretation may take place. 



Sensory data of size, distance, relative position of object and parts, 

 motion (made possible by past experience) are combined with the present 

 sensory qualities into a single phantasm of perception. This synthetic 

 product (not the naked sensory qualities) is the basis of perception. 



The old sensationalism attempted to explain perception on the basis of 

 sensory quahties. 



The Berlin school of configurational psychology transcended sensational- 

 ism by pointing out the interplay of figure and ground and the sensory 

 basis of relational perception, rejecting the very important contribution of 

 the Gratz school which insisted on the Gegenstdnde hoherer Ordnung, the 

 intellectual elements in perception. 



Pathology differentiates for us very clearly : 



{a) The awareness of sensory qualities. 



(6) The sensory synthesis. 



(c) The interpretation of sensory data. 



Prof. C. Spearman, F.R.S. — The Chicago experiments (11.30). 



Dr. R. H. Thouless. — The effect of distance on apparent velocity (12.15). 



It is a fact well known to experimental psychologists that apparent size 

 and shape are not determined only by the size and shape of the retinal 

 image of a seen object but to a considerable degree (varying with different 

 individuals) also by the real size and shape of the object itself. Thus the 

 apparent sizes and shapes of objects can be regarded as intermediate between 

 retinal and 'real' sizes and shapes. The same principle holds for apparent 

 velocity. Two objects moving with equal real velocities across the field 

 of vision at different distances from the eye have different apparent speeds, 

 the near one appearing the faster. If, however, they are moving so as to 

 give equal retinal speeds, the far one appears to be moving the faster. 

 Apparent velocity also is a compromise between retinal velocity and real 

 velocity. 



