Malgorzata Perz a,b
Raymond H. Cuijpers a
Dragan Sekulovski b
Heterochromatic flicker perception
in the periphery substantially
deviates from central vision
Introduction
LEDs can change colours over a much wider range of chromaticities and brightness
levels and with much higher frequencies than conventional light sources. Although
this is a great advantage, colour transitions can produce unattractive and undesirable
colour flicker. Previous studies already measured flicker visibility thresholds in human
central vision (Sekulovski, 2007). Here we determine visibility thresholds for
peripheral vision and compare the results to those for central vision.
a
Human-Technology Interaction, Eindhoven
University of Technology, The Netherlands
b
Philips Research Europe, The Netherlands
Results
Lightness Flicker
The visibility thresholds for Lightness flicker were independent of base colour, so we
averaged across them. Thresholds were about 1 unit ∆E higher at 35 deg in the
periphery than for central vision (panel A). Thresholds dependency on flicker
frequency was U-shaped with a minimum near 10Hz. For high flicker frequencies
(>20Hz) thresholds rapidly increase with eccentricity angle, but for low frequencies
(5Hz) the opposite pattern was observed (panel B).
Methods
Central and peripheral vision
8
Subjects performed a smooth pursuit taks in central vision. Meanwhile they pressed
a button as soon as they saw flicker of the light source in the visual periphery.
Threshold ∆Ε
7
6
5
4
35 deg
3
2
0 deg
1
A
0
5
Move the grey disk with the mouse to avoid three moving black dots
10
20
Peripheral vision
10
9
8
7
6
5
4
3
2
1
0
40
90 deg
60 deg
35 deg
B
10
5
20
40
Frequency (Hz)
The stimuli were custom built LED lamps the intensity profile of which is close to
bell-shaped. The colour was varied around a red, green or blue base colours (defined
in CIE LCh space) along the Lightness, Chroma or hue direction.
LCh colour space
Luminance profiles
Chroma and hue Flicker
Visibility thresholds for Chroma and hue ficker are about 10 times higher than for
Lightness flicker. The further into the periphery the less Chroma and hue flicker is
perceived. For Chroma flicker observers are much less sensitive around the “green”
base colour than around “blue” and “red”. In fact, Chroma variations around ”green”
are practically undetectable in the periphery of human vision. Observers are much
less sensitive to hue flicker for the red base colour.
green
red
blue
35 deg
5
10
20
90 deg
60 deg
5
10
20
5
10
Hue flicker
Threshold ∆E
Flicker frequencies were either 5Hz, 10Hz, 20Hz, 40Hz or 60Hz. The flicker
amplitudes (5 in total) differed across stimuli and were defined after pilot tests.
In the first experiment we measured the visibility thresholds for peripheral vision
(35deg, 60deg and 90deg), in the second for central vision. Thresholds were
expressed in units of the CIE LCh colour space (indicated by ∆E). For central vision
one unit ∆E corresponds the JND of static colour perception.
Threshold ∆E
Chroma flicker
80
70
60
50
40
30
20
10
0
90
80
70
60
50
40
30
20
10
0
red
green
blue
35 deg
5
10
20
90 deg
60 deg
5
10
20
5
10
20
Frequency (Hz)
Discussion and Conclusions
If flicker amplitudes are sufficiently large, some Chroma and hue changes can be perceived even at visual angles as large as 90 degrees. This is in line with Hansen et al.
(2009), who argued that cone-opponent channels, however sparse, are still present at very large visual angles. Interestingly, we found that sensitivity to Lightness flicker is
higher in central vision. Previous studies by Tayler & Hammer (1990) indicated that the retinal region of the highest flicker sensitivity is 35 degrees. However, they investigated
flicker sensitivity in terms of Critical Fusion Frequency (CFF). We computed the CFF by interpolating our Lightness curves. Indeed, we obtain the highest sensitivity for an
eccentricity of 35 deg. The very high sensitivity to Lightness flicker for low frequencies (5Hz and 10Hz) at 90 degrees is explained with the fact that although rods can detect
faint light, they cannot detect signals that modulate faster than about 10 - 15 Hz.
Our results clearly show that people can detect colour changes in the periphery, but the sensitivities deviate substantially from those in central vision. This implies that CIE’s
LCh colour space is inadeqate for peripheral vision.
References
[1] Sekulovski, D. Vogels, I.M. Beurden, M. and Clout, R. (2007). Smoothness and flicker perception of temporal color transitions, 15th Color Imaging Conference
[2] Hansen, T. Pracejus, L. and Gegenfurtner, K.R. (2009). Color perception in the intermediate periphery of the visual field, Journal of Vision, 9
[3] Tyler, C.W. and Hamer, R.D. (1990). Analysis of visual modulation sensitivity. IV. Validity of the Ferry-Porter law, Journal of the Optical Society of America A, 7, 743-758.
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