Electrical and Psychophysical Responses of the Human Visual System to Periodic Variation of Luminance

¹ Walter S. Hunter Laboratory of Psychology, Brown University, Providence, R. I.; Department of Ophthalmology, Tufts University School of Medicine, Boston, Mass. 02111
² Walter S. Hunter Laboratory of Psychology, Brown University, Providence, R. I.

The temporal resolution of the human visual system has been determined at photopic and scotopic levels of luminance, by measuring responses to periodic variations of luminance. At any given level of luminance, the contrast level of the light is varied over a range of frequencies in order to determine the minimal contrast at each frequency for eliciting a response. Three different modes of response have been explored: (1) psychophysical judgments of flicker or fusion, (2) electrical responses of the eye (electroretinogram), and (3) potentials evoked in the occipital region of the cortex (visually evoked cortical potentials). A periodic variation (contrast) of 5 per cent is sufficient typically for detection by photopic vision at low frequencies, whereas detection by scotopic vision requires significantly higher contrast. Even with 100 per cent contrast (i.e., with flashes of light separated by dark intervals of equal duration) scotopic resolution is limited to frequencies below 18 Hz, while at photopic levels the frequency range extends typically above 50 Hz. Significantly higher (above 60 Hz) resolution is shown by the electroretinogram responses than by the psychophysical or cortical responses.

Note:

A preliminary report of these experiments was given at a meeting of the National Academy of Sciences, Oct. 1969.

Key Words: electroretinogram (ERG) • visually evoked cortical potentials (VECP) • temporal resolution • scotopic contrast sensitivity • photopic contrast sensitivity

Submitted on January 11, 1971
Accepted on February 1, 1971