Wide distribution of external local sign in the normal population.

The extent of the apparent visual field was determined for a group of 78 naïve visual observers. We find that there exists a minority (less than 10%) that is essentially veridical, but that the majority of the population experiences an apparent visual field of only about 90 degrees, thus much narrower than the dioptrics of the eye would suggest (a little over 180 degrees). This is in good accordance with available (albeit mainly anecdotal) evidence, though formal data have been lacking thus far. The finding is discussed in the context of metrical calibration of the topological structure of the visual field, an aspect of "local sign".