ROUSE: THE VISUAL PERCEPTION OF DISTANCE. II7 



a range of 15 meters, the accuracy of judging the distance of an 

 approaching object is greater than in determining tliat of a reced- 

 ing one b}' the ratio of 63.05 to 58.75. 



In making estimates it was noticed that subjects quite generally 

 moved the head in different ways while looking at the objects, ap- 

 parently to give motion to the e3^e. Many were unable to tell with 

 which eye the}' saw the object, often mistaking monocular for bi- 

 nocular vision, and one kind of monocular vision for another. 

 Some subjects made their estimates quickl}', others slowly. Some 

 quickly at one time, but slowly at another. A coiuparison of the 

 results of these different subjects did not indicate that the time 

 element entered into the problem at all. Each subject required at 

 least an hour for the whole series of tests. 



(GENERAL CONCLUSIONS. 



1. There is a strong tendency to underestimate visible distances. 



2. The illusion of judging a large object to be nearer and a 

 small one farther, is less eoiiunon in biiioeiilar than in /iio/ioeitlar vis- 

 ion, although the value of this advantage must not be considered 

 too high, as it only shows a less variable relation betv/een differ- 

 ent estimates of binocular vision, all of which may be farther wrong 

 than the aggregate of monocular estimates, though severally more 

 variable. 



3. The greatest accuracy of judgment is that attained in binoe- 

 iilar vision, assisted by various clues (as size of objects, comparison 

 of other distances). 



4. When vision is in no way assisted, the order of accuracy is: 

 right eye, left eye, and botli eyes, in the ratio of .87: .86: .82 (true 

 distance being iinitv). 



5. The distance of appi-oaehing Q)h']^z\.?, is more truly judged than 

 that of receding ones, in the ratio of 63.05 to 58.75 (true distance 

 being 75.50). 



6. As the true distance increases the error steadily increases also. 



7. Distance perception has little dependence upon the time con- 

 sumed in the process. 



8. Movement of head to give motion to eye appears to be a factor 

 in distance perception. 



