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SORT Aa at TAT Bugineering Division __,, : Memorandum Report Noe MCREXD69]j—-18D 2% april 1919 the autokinetic illusion (see Guilford, J. Pe, 192%). In the accon- panying figure the line AB looks approximately as long as the line CD, but when you measure them the two will be found to be of quite different lenrths. C +> A B Visual stimuli originatints within the eye itself also rive rise to mistaken observations. Muscae volitantes or "flvingmats" are small solid particles that float about in the fluids of the eye and oast Shadows on the retina, They often can be seen when you look up at the clear aky, or when you are reading. They move as your eyes move, It is somtimes possible also to see corpuscles or other objects that are circulating within the fluids in the retina of the eye. Then, of course, everyone from time to time mistakes sane more or less familiar object for another object, A probable explanation for many reports of unidentified aerial phenomena is that the object is really something quite familiar, such as an airoraft, a light, or a bird. The observer simply fails to identify it correctly. These errors arise chiefly as a result of inability to estimate speed and distance, (2) Mistaking Imaginary for Real Events. This error of observation is usually made mwky by children, by individuals of low intelligence (people who are very suggestible), by people who see visions, or by the mentally ill, It usually is not diffioult for an Declassification Authority: NND 57565