Visual Angle
Darian S., Alyssa H., Caleb V.W., Jeremy K.,
Ly V., Joey C.
Introduction
O The size of the stimulus object and its
distance are the most important
O Retinal size is measured in degrees of visual
angle (360)
O Objects that you are perceiving are
measured in many different ways
O Inches
O Miles
O meters
What is Visual Angle
O Visual Angle = Object size/ Distance
O For any object:
O As it gets CLOSER to the viewer the visual
angle INCREASES
O As it gets FURTHER from the viewer the visual
angle DECREASES
Example: Moon and Sun
O Objects that are different sizes can still have
the same visual angle
O The Moon is 3,500km in diameter and is
380,000 km away from earth resulting in a
0.5 degree visual angle
O The Sun is 1, 400,000km in diameter and is
150,000,000km away. This also results in a
0.5 degree visual angle
How to Calculate Visual Angle
O Visual Angle= Object size/Distance
O For example: the moon
Size/ Distance = 3,500/ 380,000= .5
O Visual Angle of the sun: .5
O The larger size perfectly compensates for the increase in
distance from Earth
O How can the visual angle of two different objects be equal?
O Coffee mug (19cm), distance (90cm), visual angle
(11.92)
O Phone (12cm), visual angle (11.92), distance: ?
Activity:
http://sites.sinauer.com/wolfe3e/chap3/visangleF.htm
Visual Angle Illusion
O Look at the object on the next slide for 30
seconds
O Look at the following blank slide next
O Shift your vision to the blank wall closest to
you
O What did you see?
Visual Angle Illusion
Visual Angle Continued
O After you looked at the green dot a red
afterimage should have appeared when you
looked at the wall
O The green dot (now red) should appear
smaller on the wall than the blank slide
O Why is this?
Illusion explained
O After viewing the dot for 30 seconds the
afterimages created are “bleached out”
areas of your Retina
O This area doesn’t change in size as you
change the distance of the object that you
are looking at
O When the distance decreases, the visual
angle remains the same while the image
appears smaller