Wavelength discrimination as a function of field intensity, duration and size

Wavelength discrimination was measured in 8 normal observers as a function of test field intensity (2.5-63 td), duration (0.5-5 sec) and dia (0.5-2 degrees) to determine the conditions under which the just noticeable difference (JND) is smallest. The wavelengths of the standard and comparison hemifields were always equated for the observer's sensation luminance. For field intensity and duration, the wavelength JND was found to decrease until these parameters were increased beyond a certain value--25 td and 1.0 sec, respectively--and to remain constant thereafter. For field diameter, however, the JND was smallest only within a very limited range of values--between 1.0 and 1.5 degrees--and increased sharply with smaller and larger values.