Version 0.10 (c) 2007 CELEST VISI  N Star Light, Star Bright, Let’s Explore Light How You Perceive Light How many black dots can you count?

Version 0.10 (c) 2007 CELEST HOW DO WE SEE?

Version 0.10 (c) 2007 CELEST DO WE SEE LIKE A CAMERA? Unlike a camera, human vision is a perceptual process involving many parts of the brain. or digital sensor

Version 0.10 (c) 2007 CELEST What do we need in order to see? A source of light A source of reflected light an eye to receive light

Version 0.10 (c) 2007 CELEST When light falls on a surface, some of it is absorbed and some of it is reflected. HOW DO WE SEE OBJECTS THAT DO NOT PRODUCE LIGHT? reflected absorbed Our eyes can detect the reflected light.

Version 0.10 (c) 2007 CELEST DARK AND LIGHT SURFACES absorb most of the light that falls on them, and reflect little. reflected absorbed reflected absorbed Dark surfaces Light surfaces absorb little of the light that falls on them, and reflect most.

Version 0.10 (c) 2007 CELEST HOW DO WE SEE THINGS IN THE DARK? You can’t see in total darkness, because you need light to see. However, you can see if there is a little light. But how?

Version 0.10 (c) 2007 CELEST EDGE DETECTORS! Vision is sensitive to the difference or contrast between two surfaces. In terms of vision, contrast is the comparison between the reflected light of one surface and another. A comparison is computed as a ratio of two measures. How does contrast affect which owl you see in each picture?

Version 0.10 (c) 2007 CELEST HOW DO WE KNOW WHAT IS GOING ON AROUND US? Vision, one of the five senses, controlled by specific types of cells, that send messages to a specific part of the brain. Name the other four senses. All of the senses are controlled by different types of cells that send messages to different parts of the brain.

Version 0.10 (c) 2007 CELEST OUR FIVE SENSES LET US PERCEIVE THE WORLD Smell and Taste Vision Touch Hearing Back of head Front of head

Version 0.10 (c) 2007 CELEST WHAT IS “PERCEPTION”? Some perceptions are illusory. Perception is the process of acquiring, “interpreting,” selecting, and organizing sensory information. Do you always see what is “really” there?

Version 0.10 (c) 2007 CELEST WHITE’S ILLUSION How many shades of gray are in the picture?

Version 0.10 (c) 2007 CELEST WHITE’S ILLUSION Only one!

Version 0.10 (c) 2007 CELEST Are squares A and B the same shade of gray? ADELSON’S CHECKERED SHADOW ILLUSION

Version 0.10 (c) 2007 CELEST Yes! ADELSON’S CHECKERED SHADOW ILLUSION

Version 0.10 (c) 2007 CELEST How does the human brain and eye accomplish the task of perceiving?

Version 0.10 (c) 2007 CELEST THE HUMAN EYE The eye is actually an organ in the shape of a ball. From the outside you can see the pupil and the iris. The pupil is what lets light inside the eye. Pupil Iris The human eye is very complex

Version 0.10 (c) 2007 CELEST Inside the Eye… The lens directs the light to the retina at back of the eye where the photoreceptors receive the light and send information to the brain via the optic nerve. THE HUMAN EYE Lens Retina Optic Nerve Pupil Iris

Version 0.10 (c) 2007 CELEST VISION AND THE BRAIN Light stimulates photoreceptors sending messages to the visual cortex.

Version 0.10 (c) 2007 CELEST THE VISUAL PATHWAY Adapted from Frisby 1979

Version 0.10 (c) 2007 CELEST BASIC DEFINITIONS REFLECTED LIGHT Illuminant Illuminance Luminance Photoreceptors on the retina Based on the diagram, define illuminant, illuminance, luminance, and photoreceptor.

Version 0.10 (c) 2007 CELEST BASIC DEFINITIONS Brightness Perception Define reflectance and brightness perception. Reflectance