TARGET CODING BY MEANS OF VISUAL FLICKER.
JOHNS HOPKINS UNIV BALTIMORE MD PSYCHOLOGICAL LAB
Pagination or Media Count:
Conclusions Flicker used for coding must be coarse flicker, not fine flicker. Therefore, it will be necessary to stay well below the fusion frequency at all times. The range of frequencies available for scaling into a usable code system is from about one-half to not more than 45 flashes per second. The upper value is probably too high and it may well be that 30 fps is a better figure. To obtain 45 fps without fusion, retinal intensities of about 1000 millilamberts are required. For 30 fps, this value is about 10 millilamberts. It seems likely that little discriminable difference will be found between frequencies from 20 to 40 fps i.e., flicker at 20 fps will look much like flicker at 30 or 40 fps. The more readily distinguishable steps will be found under 20 fps. The number of discriminable steps between one-half fps and 30 fps is unknown. This is also true of the reliability of such discriminations which may be a matter of practice. Crude observations suggest that about 15 steps are what can be expected. Factors such as the area and position of the retine affected by flicker are of undetermined importance in the practical application. However, it appears that the size of the retinal image should not be appreciably under two degrees and that the targets should always be viewed along the line of sight. It seems likely that using flashes of light in certain special patterns of intermittence would be a profitable area to explore. Author