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Canada (162,359)
Psychology (3,337)
PSYC 2390 (118)
Lana Trick (87)
Chapter 3

Chapter 3

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Department
Psychology
Course
PSYC 2390
Professor
Lana Trick
Semester
Winter

Description
Chapter 3Intro to Vision Focusing Light onto the RetinaVision is based on visible light which is a band of energy within the electromagnetic spectrumproduced by electric charges and is radiated as wavesCan be described by its wavelength distance between the peaks of the electromagnetic waves which range from extremely shortwavelength gamma raysto longwavelength radio wavesVisible light is what humans can perceive having wavelengths ranging from 400 to 700 nanometersLight can also be describes as consisting of small packets of energy called photons with one being the smallest unitIn the wye light reflected from objects in the environment enters the eye through the pupil and is focused by the cornea and lens to form sharp images of the objects on the retina which contain the receptors for visionRods and cones are the receptorsthey contain lightsensitive chemicals called visual pigments that react to light and trigger electrical signalsthe signals flow through the network of neurons that make up the retina and then emerge from the back of the eye in the optic nerve which conducts signals toward the brainThe cornea accounts for 80 of the eyes focusing power but like the lenses in eyeglasses it is fixed in place so cant adjust its focus so the lens supplies the remaining 20 of focusing power and can change its shape to adjust the eyes focus for stimuli located at different distancesIf an object is far away the light rays that reach the eye are parallel and these parallel rays are brought to a focus on the retina but the object moves closer the light rays reflected from this obect enter the eye at more of an angle pushing the focus behind the retina but the image is stopped before this making it out of focusaccommodation keeps this from happening the ciliary muscles at the front of the eye tighten and increase the curvature of the lens so that it gets thicker it bends the light rays passing through the lens to pull the focus point back to the original spot to create a sharp image on the retinaThe distance at which your lens can no longer adjust to bring close objects into focus is called the near pointthe distance of the near point increases as a person gets older presbyopiaold eye the near point for most 20 year olds is 10 cm but increased to 14 cm by age 30 22 cm at 40 and 100 cm at 60Myopia or nearsightedness is the inability to see distant objects clearlyaffects 70 million Americansthe myopic eye brings parallel rays of light into focus at a point in front of the retina so that the image reaching the retina is blurred which can be caused by either 1 refractive myopia cornea and les bends the light too much or 2 axial myopia eyeball is too longmove the stimulus closerthe distance at which the spot of light becomes focused on the retina is called the far point when the spot of light is at the far point a myope can see it clearlyLASIK laserassisted in situ keratomileusis more than 1 million Americans have this surgery which sculpts the cornea with an excimer laser and a small flap is cut onto the surface the flap is
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