J.— PSYCHOLOGY 207 



most people are unaware of these differences until they have been shown 

 to them by e^fperiment. This, however, should not surprise us when we 

 remember that most psychological individual differences remain un- 

 suspected until revealed by measurement. The enormous individual 

 differences in imagery, for example, are not generally known, and most 

 people imagine that others have much the same equipment of imagery as 

 themselves. In the same way, a colour-blind person is rarely aware of 

 the difference between his own and other people's colour perception 

 unless his attention is drawn to it by his inability to perform some task 

 such as that of recognising the difference between red-covered and green- 

 covered wires in a cable. 



So it is with phenomenal regression. The shapes and sizes of objects 

 in the phenomenal world differ widely for two people from the same 

 view-point, but they are not aware of this difference since neither can see 

 the world through the other's eyes and they have generally no occasion 

 to discuss apparent shapes and sizes. One can, however, easily start a 

 dispute between a group of people when driving through the country by 

 asking them whether the cows in a distant field look larger or smaller 

 than a sparrow perched on the hedge. The answers will be very different 

 and each will think that he is giving the only reasonable answer and that 

 others must have misunderstood the question. They will not easily 

 understand that the origin of the different answers is that the phenomenal 

 world does really look different to different persons. 



We may ask the question : Are there any laws governing these changes 

 of phenomena with changing distance, inclination, and illumination, 

 other than the fact that they differ from one individual to another (a fact 

 which suggests lawlessness rather than law) and that their amounts tend 

 to be approximately the same for any one individual ? It might be 

 possible that there were no invariant relationships within these indi- 

 vidual variations, and, however unsatisfactory that situation might appear 

 to the scientific mind, it might be necessary to accept it. It does not 

 appear, however, that things are as bad as this. I have found one invariant 

 relationship, within a certain range of distances, for phenomenal size. 



If we measure, for a given individual, the apparent size of a disc at 

 different distances we find that its linear dimensions decrease as the 

 distance becomes greater, this decrease becoming slower as the distance 

 is increased (as, of course, do the linear dimensions of the retinal image). 

 The decrease of apparent size is always much slower than the decrease of 

 retinal size (in accordance with the principle of phenomenal regression), 

 and with those individuals who have high phenomenal regression it is much 

 slower than with others. If apparent size is plotted on a graph against 

 distance, therefore, we have a curved line, which, so far, gives us no law. 



If we now plot on a graph the apparent linear size of the disc at various 

 distances for any one individual against the stimulus size (that is, against 

 a size proportional to the retinal projection), a law emerges. All the points 

 plotted fall on a straight line inclined upwards from the P axis. If pro- 

 jected backwards towards the P axis it would not pass through the origin 

 but would intersect the P axis above the origin. This means that the 

 relation between phenomenal and stimulus linear dimensions of the object 

 at different distances can be expressed by the equation P = a + b . S. 



