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Chapter 3

Chapter 3

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University of Guelph
PSYC 2390
Lana Trick

PSYC 2390 Sensation and Perception Chapter 3 Introduction to Vision Focusing Light onto the Retina Vision begins when visible light is reflected from objects into the eyeLight The Stimulus for Vision Lighta band of energy within the electromagnetic spectrumElectromagnetic Spectrum a continuum of electromagnetic energy that is produced by electrical charges and is radiated as waves Photon the smallest possible particle of light energy Wavelength the distance between the peaks of the electromagnetic waves wavelengths range from extremely short gamma rays about 110 000 000 000 m toextremely long radio waves 10 000 m wavelengths ranging from 400700 nmThe wavelength of visible light is associated with the different colours of the spectrumThe Eye Light reflected from stimuli in the environment enters the eye through the pupil and is focused by the cornea and lens to form sharp images of the object on the retina which contains the receptors for vision Two kinds of visual receptors 1 Rods 2 Cones Visual Pigments lightsensitive chemicals in the visual receptors that react to light and trigger electrical signals The electrical signals triggered by visual pigments flow through the network of neurons that make up the retina The signals then emerge from the back of the eye in the optic nerve which conducts signals toward the brainLight is Focused by the Eye Once light is reflected from an object into the eye it needs to be focused onto the retina The cornea transparent covering of the front of the eye accounts for 80 of the eyes focusing power The lens supplies the remaining 20 of the eyes focusing power by changing shape to adjust the eyes focus for stimuli located at different distancesAccommodation the process in which the ciliary muscles at the front of the tighten toincrease the curvature of the lens to bend the light reflected fromobjects that are close by or relax for the light that is reflected fromobjects that are at distance light does not need to be bentVision Problems Related to Light Focusing Near Point the distance at which ones lens can no longer adjust to bring close objects into focus Far Point the distance at which a point of light is focused onto the retina
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