Minimum exposure time?

Michael Hucka hucka at
Tue Dec 6 17:36:09 EST 1994

I've been trying to determine what is the minimum presentation time of a
visual stimulus that will allow a human observer to extract *some*
information.  Of course, this is going to be very task- and
experience-dependent, but for recognizing simple forms or making simple
discriminations, what is generally accepted as being a valid lower limit on
exposure time?

>From what I've been able to determine, 20 msec exposure, when followed by a
pattern mask, is pretty much the shortest feasible viewing time.  This comes

 * Sperling, in his visual search work in the early 1970's, used a technique
   of flashing arrays of letters and asking observers to detect the presence
   of a numeral in one of the arrays [G. Sperling & M.J. Melchner, "Visual
   search, visual attention, and the attention operating characteristic",
   _Attention and Performance VII_, ed. Jean Requin, 1978].  Each array in a
   sequence contained a set number of letters, from two to twenty-five, and
   was flashed for a fraction of a millisecond, with a uniform (grey?) field
   displayed between presentations of arrays for a (constant) period varying
   from 10 msec to 320 msec.  Because the arrays were presented sequentially
   back to back, each new stimulus acted as a pattern mask for the previous
   one.  In his experiments, observers seemed to have a non-zero probability
   of being able to detect a target with 20 msec presentation times in 2-item

 * Biederman, in work in the late 1970's, used a forced-choice scene
   recognition test with presentation times as low as 20 msec (e.g.,
   [Biederman, Rabinowitz, Glass and Webb, "On the information extracted from
   a glance at a scene", J. Exp. Psych., 103(3):597-600, 1974].)  One of the
   experiments involved presenting pictures of common scenes (e.g., a
   ``shopping plaza'') to subjects for 20 to 4000 msec, followed by a pattern
   mask for 300 msec, and then followed by a discrimination test in which the
   subject had to select between two verbal labels (words or phrases)
   describing the scene.  When the scene labels were dissimilar (e.g.,
   ``shopping plaza'' versus ``kitchen''), subjects averaged approximately
   65% correct responses at 20 msec and over 70% correct at 50 msec.
   Performance, however, was worse when the labels were similar (e.g.,
   ``shopping plaza'' versus ``busy road and stores''); subjects averaged 55%
   correct responses at 20 msec and 65% correct at 50 msec.

But 20 msec seems awfully short to me, so I wanted to check with others and
ask if this seems reasonable.
   Mike Hucka (michael.hucka at
   University of Michigan, Ann Arbor, Mich.

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