eye tracking meeting

Eye Tracking Meeting Chap. 3 Visual Psychophysics

Hayato Maki (AHC-Lab, NAIST) 2/12/2016

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

Visual Angle

Table 3.1. When looking at a U.S. quarter coin… Distance AngleArm’s length 1.5°-2°

85m 1 minute5km 1 second

Eye

A S

D

Looking from above

Object

AD

S

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

Visual Acuity (視力)

• At 5°, acuity is only 50%.

Acuity Visual AngleHighest A < 2°Higher A < 4°~5°↓̶ Acuity sharply drop off ̶↓Useful A < 30°Poor A > 30°

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.

Fovea (中心窩)

Fovea

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

Distribution of Cones and Rods

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.

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)

cont

rast

sens

itivi

ty

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.

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.

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.

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.

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.


• 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.


• 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.

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