THE SENSE OF VISION. 353 



Our estimate of the size of given lines, angles, and areas is influenced by 

 neighboring lines, angles, and areas with which they are compared. This 

 influence is sometimes exerted in accordance with the principle of contrast, 

 and tends to make a given extension appear larger in presence of a smaller. 

 and smaller in presence of a larger extension. This effect is illustrated in 



Fig. 168.— To illustrate so-called " confluxion " in space-perception (Muller-Lyer). 



Figure 165, in which the middle portion of the shorter line appears larger 

 than the corresponding portion of the longer line, in Figure 166, in which a 

 similar effect is observed in the case of angles, and in Figure 167, in which 

 the space between the two squares seems smaller than that between the two 

 oblong figure's. 



Fig. 169.— To illustrate so-called "confluxion" in space-perception (Muller-Lyer). 



In some cases, however, an influence of the opposite sort 1 seems to be 

 exerted, as is shown in Figure 168, in which the middle one of three parallel 

 lines seems longer when the outside lines are longer, and shorter when they 

 are shorter than it is itself, and in Figure 16S), in which a circle appears larger 

 if surrounded by a circle larger than itself, and smaller if a smaller circle is 

 shown concentrically within it. 



Fig. 170.— To illustrate the Influence of angles upon the apparent length of lines (Muller-Lyer). 



Lines meeting at an angle appear longer when the included angle is large 

 than when it is small, as is shown in Figure 17<>. This influence of the 

 included angle affords a partial explanation of the illusion shown in Figure 

 171, in which the horizontal line at B seems longer than at A ; but the distance 



1 For this influence the name "confluxion " lias been pro posed by Miiller Lyer, from whose 

 article in the Archivfiir Phygiologie, 1889, Sup. Bd., the above examples arc taken. 

 Vol.. II.— 23 



