Sensation and PerceptionSensation and Perception

Sensations: take it inSensations: take it in Perception: what we do with itPerception: what we do with it

VisionVision

The eye receives light waves and The eye receives light waves and converts energy into neural converts energy into neural impulses by a process called impulses by a process called Transduction.Transduction.

http://www.exploratorium.edu/learning_studio/cow_eye/video_big_all.htmlhttp://www.exploratorium.edu/learning_studio/cow_eye/video_big_all.html

Wavelength = hueWavelength = hue Amplitude = brightnessAmplitude = brightness

Blue Man GroupBlue Man Group

http://www.youtube.com/watch?v=W-yLfmhttp://www.youtube.com/watch?v=W-yLfm5HsHc5HsHc

Rods and Cones are the visual Rods and Cones are the visual receiversreceivers

Rods: process black and white.Rods: process black and white.– denser on the outside, active in dim light,denser on the outside, active in dim light,

Cones: processes colorCones: processes color– clustered mainly in the center of the eye’s clustered mainly in the center of the eye’s

focus, focus, the foveathe fovea– Needs bright light to functionNeeds bright light to function– turns off in dim lightturns off in dim light– processes with more sharpness than rods.processes with more sharpness than rods.

Color visionColor vision

Young-Helmholtz Trichromatic Young-Helmholtz Trichromatic TheoryTheory: : there are three types of cones there are three types of cones each sensitive to the primary colors (red, each sensitive to the primary colors (red, blue, green). blue, green).

– The brain mixes the sensations from those to The brain mixes the sensations from those to create all the perceived colors we see. create all the perceived colors we see. Color Color blindness: people lack receptors for one of blindness: people lack receptors for one of the three.the three.

Two theories within a theory – do we add or Two theories within a theory – do we add or subtract? subtract? Depends on the situationDepends on the situation

Coloring book – additiveColoring book – additive Theater lighting - subtractiveTheater lighting - subtractive

ProblemsProblems

If the lens or cornea is If the lens or cornea is distorteddistorted in in relation to the eye then it effects the relation to the eye then it effects the acuity acuity or sharpness of the image seenor sharpness of the image seen. .

One is said to be either nearsighted or One is said to be either nearsighted or farsighted when this occurs.farsighted when this occurs.

The ProcessThe Process Light energy hits the rod or cone which Light energy hits the rod or cone which

creates a photochemical reaction creates a photochemical reaction Photochemical reaction creates an Photochemical reaction creates an

electrical impulse sent to electrical impulse sent to bipolar cellsbipolar cells, , which funnel the electricity to which funnel the electricity to ganglion cellsganglion cells

Ganglion cells, whose combined axons Ganglion cells, whose combined axons create the create the Optic Nerve,Optic Nerve,

which leads to the brain. The spot which leads to the brain. The spot where the where the Optic nerveOptic nerve leaves the eye leaves the eye is a is a blind spot.blind spot.

Color VisionColor Vision Opponent process theoryOpponent process theory: : states that some states that some

neurons receive one color and are turned off by neurons receive one color and are turned off by another. another.

– For instance, a neuron can detect red, but another is For instance, a neuron can detect red, but another is turned off by it, so you can’t see shades of certain turned off by it, so you can’t see shades of certain combinations reddish green. This theory is used to combinations reddish green. This theory is used to explain afterimages, where you wear out the explain afterimages, where you wear out the response in one neuron for one color and then can response in one neuron for one color and then can only see the opposing color when staring at a white only see the opposing color when staring at a white board, until the neuron replenishes.board, until the neuron replenishes.

http://www.grand-illusions.com/optihttp://www.grand-illusions.com/opticalillusions/amazing_dots/calillusions/amazing_dots/

Visual ProcessingVisual Processing

Feature detectorsFeature detectors: : Separate neurons and Separate neurons and neural neural networks in the brainnetworks in the brain which which are are sensitive to specific stimuli, sensitive to specific stimuli, angles, lines, edges, shapes or angles, lines, edges, shapes or movementsmovements– allowing the brain to differentiate allowing the brain to differentiate

individual objects or movements to individual objects or movements to concentrate on.concentrate on.

Where feature detectors detect.Where feature detectors detect.