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Perception and cognition lec 2.docx

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University of Toronto Scarborough
Matthias Niemeier

Perception and cognition lec 2  Physics, optics o Light: a wave, stream of photons, tiny particles that each consist of one quantum of energy. o We are sensitive to 400-700 nanometers in wavelengths  Absorbed: energy is taken up by a medium and transformed to another form of energy  Transmitted: convey light from one place to another through a transparent medium  Reflected: energy that is redirected when it strikes a surface  Purkinje reflections, eye movements o When shining light on an eye, you typically see 4 reflections of light on that eye. (front/back of schlera, front/back of lense) o Eye tracking uses this  Diffracted: Bent or having waves that are spread out, (e.g., waves of sound or light as they encounter an obstacle, e.g. pass through a narrow apature)  Refracted: Energy is altered in its path as it passes into another medium, (eg: light passing through air, and then water)  Light gets bent, therefore a pencil in water looks bent  Works with lenses too o Most important sense  Advantage over touch in detection from a distance. o Evolution of the eye  Eye spots  Photosensitive pigments with which you can sense light, information is passed to brain.  Depression in photoreceptors can help indicate where light is coming from, but work better with a smaller aperture. o “pinhole” eye allows finer directional sensitivity and limited imaging.  Light sensitive protein: opsin  Development of membrane to cover cavity. Transparent humor develops inside.  Lens develops to more accurately refract light  Iris and separate cornea develop  Cornea in humans has stronger refraction rate than lens o Learn all components of the eyeball on slides o Refraction is necessary to focus light rays. This is done by the four optical components.  The ciliary muscles change the shape of the lens, and thus alters its refractive power.  The closer an object, the more the ciliary muscles contracts to bend the light onto the same point on the retina  This is called accommodation o Myopia is caused by the eyeball being too long for the lens  Refractory power of the lens is stronger than it has to be, light points diverge on the retina o All blood vessels converge on the optic disk o Light must pass through many structures in retina before hitting the photoreceptors  It is a bit illogical because it is not processed until it hits photoreceptors.  Information is then passed on to horizontal/bipolar cells, then ganglion cells. o Photoreceptors: cells in the retina that initially transducer light energy into neural energy. Duplex retinas:  Rods: Photoreceptors that are specialized for night = scotopic vision (90 million)  Cones: Photoreceptors that are specialized for daylight = photopic vision, fine visual acuity and color (4-5 million)  Some animals have mostly rod retinas  3 photoreceptor for circadian rhythm o Fovea is not sensitive enough for night vision o Visual pigments are molecules with two parts  Chromosphore (captures photons)
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