Abstract
The relationship between luminous intensity and the max-
imum frequency of flicker that can be detected defines the
limits of the temporal-resolving ability of the human visual
system. Characterizing this relationship has important the-
oretical and practical applications and it is best described
by the Ferry-Porter law, which states that critical flicker
fusion (CFF) increases as a linear function of log retinal
illuminance. This law has been shown to hold for a wide
range of stimulus over four orders of magnitude; however,
beyond this, it is unknown if the CFF continues to increase
linearly. We determined the flicker fusion threshold for
five participants over six orders of magnitude at 35 eccen-
tricity. Our results show that up to 104 Trolands, the data
conform to the Ferry-Porter law with a similar slope as
previously established for this eccentricity (22 Hz/decade)
and a maximum average threshold of 77 Hz (5 Hz); how-
ever, beyond this value and up to 106 Trolands, the CFF
function flattens with a slope that falls within the error of
the measurements (4 Hz/decade). We conclude that for
35 eccentricity the Ferry-Porter law holds over four
orders of magnitudes, after which point, saturation is
reached and the time constant no longer decreases with
increasing luminous intensity.
