VISUAL ANGLES (3.1) BY ANIKA, ANGELA, DUY, HANNAH, LYDIA AND VALCIA INTRODUCTION • Visual Angle can be defined as the angle subtended by an object at the retina. • An important aspect of any stimulus is the size of the stimulus. • There is a crucial distinction to be made between the size of an object in the world and the size of the same object projected on the retina. • Object Size in the world is measured in millimeters, inches, miles etc. • Retinal size is measured in degrees of VISUAL ANGLE. • Visual Angle incorporates both the size of the object and its distance from the observer. WHAT IS THE VISUAL ANGLE? • Visual Angle ≈ • Visual angle is measured in degrees • 360° represents the entire circumference of the eyeball • Problem? • Visible area is at the back of the eye (the part of the world we can see) ≈ 180° THE SUN AND MOON Moon: Visual angle = 0.5 degrees Sun: Visual angle = also 0.5 degrees! • Even though the sun is farther away, it’s diameter is larger, which compensates for the extra distance. • Because the visual angles are the same, that’s why we can still see a ring of sun behind the moon during a solar eclipse. VISUAL ANGLE CALCULATOR • Visual Angel= Object size/ Distance • For example, to calculate the visual angel when we look at the moon. We have moon’s diameter/ Distance = 3,500/ 380,000= 0.5 • Or How to calculate a size of an object when we have eye visual angel is 5 degrees and the distance is 50 cm. we have the size is 4.4 THE VISUAL ANGLE ILLUSION Illusion that depicts the visual angle WHY DOES THE CIRCLE CHANGE SIZES? The distance changes the visual angle doesn’t Visual Angle = Object Size/ Distance • Distance (from computer)= 70cm • Visual Angle = 2° • Object Size = 2.5 cm • • • • Distance (from paper) = 15 cm Visual Angle = 2° Object Size = .5 cm Who cares? REFERENCES • http://sites.sinauer.com/wolfe3e/chap3/visangleF.htm • Wolfe, J., Kluender, K., Levi, D., et al. (2012). Sensation & perception. (3rd ed.). Massachusetts: Sinauer Associates, Inc.