To investigate psychological determinants of the fact that perception is often nonveridical, stimulus items (mostly groups of letters) were presented tachistoscopically to 100 subjects. A 50-msec. exposure maximized opportunity for misperception. A substantial proportion of subjects misperceived, and as many as 88% reported identical misperceptions of various stimulus items. Many of the misperceptions were regularizations of the stimulus in the direction of the more familiar, i.e., transformations in the direction of a similar physical stimulus frequently encountered in the past. Results are explained in terms of principles of (1) perceptual insertion (UNIVERITY became UNIVERSITY), (2) perceptual deletion (HOSPPITAL became HOSPITAL), (3) perceptual transposition (WAHSINGTON became WASHINGTON), and (4) perceptual modification (UNCONSCIOUS became UNCONSCIOUS). These processes are believed to operate in ordinary everyday observation.