This document summarizes key aspects of visual psychophysics discussed in Chapter 3, including: 1. Spatial and temporal vision properties like visual acuity and the phi phenomenon. 2. Anatomy of the eye including distribution of photoreceptor cells and higher density in the fovea. 3. Perception of motion, color, and luminance in the visual periphery compared to the fovea. 4. Implications for attentional design of visual displays to accommodate differences between foveal and peripheral vision.

1. Eye Tracking Meeting
Chap. 3 Visual Psychophysics
Hayato Maki (AHC-Lab, NAIST)
2/12/2016

2. Contents
• Spatial Vision
• Temporal Vision
• Perception of Motion in the Visual Periphery
• Sensitivity to Direction of Motion in the Visual
Periphery
• Color Vision
• Implications for Attentional Design of Visual Displays
• Summary and Further Reading

3. Visual Angle
Table 3.1. When looking at a U.S. quarter coin…
Distance Angle
Arm s length 1.5 -2
85m 1 minute
5km 1 second
Eye
A S
D
Looking from above
Object
A
D
S

4. Visual Field
Major Horizontal Axis
(looking from above)
Minor Vertical Axis
(looking from side)
0°< A <180° 0°< A <130°
The entire visual field
= 180° × 130° = 23400 square degree

5. Visual Acuity (視力)
• At 5°, acuity is only 50%.
Acuity Visual Angle
Highest A < 2
Higher A < 4 5
↓̶ Acuity sharply drop off ̶↓
Useful A < 30
Poor A > 30

6. Photoreceptor Cells (光受容細胞)
•Photorecepter cells are cones (錐体) and rods
(桿体).
‣ Cones support daytime vision and color
perception.
‣ Rods support dim-light vision and black-
and-white vision.
•Cones makes the largest contribution to
deeper brain centers and spatial resolvability.

7. Fovea (中心窩)
Fovea
• It contains closely
packed cones
(147,000 cones/
mm2) and no
rods.

8. Distribution of Cones and Rods

9. Temporal Vision (Visual Response to Motion)
• Human visual response to motion is
characterized by 2 facts.
• Persistence of vision (視覚の残存？),
temporal sampling rate of human visual
system.
• Phi phenomenon (ファイ現象),
a threshold above which the human visual
system detects apparent movement.

10. Persistence of Vision
• The retina (網膜) can not
same rapidly changing
intensities.
• A stimulus flashing at about
50-60 Hz (Critical Fusion
Frequency) will appear
steady.
• This is the reason why
flicker is eliminated in
motion picture and
computer displays.
temporal frequency (Hz)
contrastsensitivity

11. Phi phenomenon
• When viewed in rapid succession, a series of
images are perceived as continuous motion.
• This explains the illusion of old-fashioned
moving neon sign.

12. Perception of Motion in the Periphery
• The fovea is more receptive to slower motion
than periphery.
• The velocity of a moving target appears slower
in the periphery than in the fovea.
• At higher velocities, the effect is reversed.

13. Color Vision
• Color vision is given by 3 types of cones, roughly
corresponding to red, green and blue.
• Of the 7 million cones, most are tightly packed into the
central 30° region of the fovea.
• Hence, peripheral color vision is quite poor.

14. Peripheral Color Vision
• Fig. 3.7. shows visual fields for right eye.
• There is much yet to be learned about peripheral vision.
Fig.3.7.

15. Implications for Attentional Design of Visual Displays 1
• Both the structure and functionality of
human visual system components place
constraints on the design of a visual
communication system.
• Particularly, foveal and peripheral vision
must be distinguished.

16. Implications for Attentional Design of Visual Displays 2
• Spatial resolution should remain high within
the foveal region, and smoothly degrade
within peripheral region.
• Temporal resolution must be available in the
periphery. Sudden onset events are potential
attentional attractors.
At low speed, motion of peripheral targets
should be increased to match apparent
motion in the central view.

17. Implications for Attentional Design of Visual Displays 3
• Luminance (輝度) should be coded for high
visibility in the peripheral areas because the
periphery is sensitive to dim objects.
• Chrominance (色度) should be coded for high
exposure almost exclusively in the foveal
region, with chromaticity decreasing sharply in
to the periphery.
• Contrast sensitivity should be high in the
periphery.