140 HAROLD C. BINGHAM 



It is not to be denied that a triangle with vertex up differs 

 from a triangle with vertex down. But we can scarcely say that 

 they are two different forms. They are both triangles; yes, 

 more than that: they are equilateral triangles. Where they 

 differ is not in form but in shape. When the extended base of the 

 triangle is so placed as to stimulate the region of the retina 

 which was formerly stimulated by the vertex of the triangle, a 

 condition occurs similar to that pointed out regarding Lashley's 

 ' forms:" the forms remain identical, but the lines of maximum 

 and minimum extension have interchanged. This fact led me 

 to conclude in my paper 8 that the apparent reactions to forms are 

 the result of keen perception of size differences. I might have said 

 they are due to perception of shape differences. The inversion 

 of the triangle causes certain particular size changes — vertex 

 or point interchanged with base or line — which causes a change in 

 shape, but no general change of size since the area remains con- 

 stant. Similarly the factor of triangularity remains constant 

 and the form is unchanged. Not ' the perception of form," 

 therefore, but the perception of shape ' is based precisely on 

 the unequal stimulation of different parts of the retina." 



Our definition, then, as separate from the distinction between 

 forms and patterns, must draw a line between forms and shapes. 

 Referring to the retinal area stimulated, there is form which is 

 general, e.g., triangle. But there is a particular feature about 

 this general distribution of light — it is equilateral, or isosceles, or 

 right angled — viz., shape. Forms are identical when their 

 areas are equal and their general retinal distribution is similar. 

 Shapes are identical when all extensions of the identical forms 

 are equal and in the same relative directions. Thus, the area 

 remaining constant, either or both form and shape may change. 

 The form remaining constant, the shape may change. Change 

 in form must always cause change in shape. 



Subsequent studies in this field should not fail to consider the 

 factors of ' shape ' and ' ' pattern ' in their relation to form 

 perception. Whatever system of control is adopted, such possible 

 disturbances as these factors must be considered and, as far as 

 possible, eliminated and isolated. Unquestionably my final test 

 for form discrimination by shifting the position of the form was 

 a severe one. Surely the factor of shape was a disturbing in- 



8 Op. Cit., p. 110. 



