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PSYB51 cont'd
Chapter 2 & Lecture 2
| Question | Answer |
|---|---|
| Light | a form of electromagnetic radiation--- energy produced by vibrations of electrically charged material |
| Wave | an oscillation that travels through a medium by transferring energy from one particle or point to another without causing any permanent displacement of the medium |
| Photon | a quantum of visible light or other form of electromagnetic radiation demonstrating both particle and wave properties |
| Visible light waves | have wavelengths b/w 400 and 700 nanometers (nm) |
| Gamma rays | have very short wavelengths |
| Radio & television | have long wavelengths |
| Absorb | to take up light, noise, or energy and not transmit it at all |
| Scatter | disperse light in an irregular fashion |
| Reflect | to redirect something that strikes a surface- especially light, sound, or heat- usually back toward its point of origin (i.e. mirrors) |
| Transmit | to convey something (e.g. light) from one place or thing to another |
| Refract | (1) to alter the course of a wave of energy that passes into something from another medium, as water does to light entering it from the air. (2) to measure the degree of refraction in a lens or eye |
| Image | a picture or likeness |
| Cornea | the transparent “window” into the eyeball; made up of a highly ordered arrangement of fibers & contains no blood vessels or blood, which would absorb light |
| Cornea has | a rich supply of transparent sensory nerve endings, which are there to force the eyes to close and produce tears if the cornea is scratched, preserving its transparency. |
| Transparent | allowing light to pass through with no interruption so that objects on the other side can be seen clearly. |
| Amoebas | respond to light, changing their direction of motion to avoid bright light when it is detected |
| Eye | can form an image of the outside world, enabling animals that possess eyes to use light to recognize objects, not just to determine whether light is present and what direction it is coming from |
| Aqueous humor | watery fluid in the anterior chamber of the eye; fills the space immediately behind the cornea, supplying oxygen and nutrients to & removing waste from, the cornea and the crystalline lens |
| Crystalline lens | the lens inside the eye that enables changing focus; has no blood supply, is completely transparent and the shape of the lens is controlled by the ciliary muscle |
| Pupil | the dark circular opening at the center of the iris in the eye, where light enters the eye; controls the amount of light that reaches the retina via the pupillary light reflex |
| Iris | the colored part of the eye, consisting of a muscular diaphragm surrounding the pupil regulating the light entering the eye by expanding and contracting the pupil |
| “photic sneeze reflex” | emerging from a dark room into bright light the pupils will constrict but also a high chance of sneezing in response to the exposure to bright light; possibly a result of crossed wires in the brain |
| Vitreous humor | the transparent fluid that fills the vitreous chamber in the posterior part of the eye; vitreous chamber- located in the space between the lens and retina) |
| Floaters | common biodebris that drift around in the vitreous |
| Retina | light-sensitive membrane in the back of the eye that contains rods and cones, which receive an image from the lens & send it to the brain through the optic nerve; tell brain abt aspects of light that are related to the objects of the world |
| Accommodation | process by which the eye changes its focus (the lens gets fatter as gaze is directed toward nearer objects); allows lens to vary as much as diopters |
| Presbyopia | “old sight”; the loss of near vision because of insufficient accommodation; lens becomes sclerotic & capsule around lens loses elasticity |
| Cataract | Opacity of the crystalline lens; caused by irregularity of the crystalline lens; absorb & scatter more light than the normal lens |
| Refractive forces in the eye that are fixed | cornea- most powerful, aqueous humor and vitreous humor |
| Zonules of Zinn | tiny fibers; ciliary muscle is relaxed the zonules are stretched & lens is flat therefore the eye will focus on distant objects. Ciliary muscle must contract to view something closer & this contraction reduces tension on zonules & allows lens to bulge |
| Benjamin Franklin | invented bifocals; power at the top to view distant objects and power at the bottom to view near objects comfortably |
| Emmetropia | condition where there is no refractive error, b/c refractive power of the eye is perfectly matched to the length of the eyeball |
| Myopia- nearsightedness | condition in which light entering the eye is focused in front of the retina & distant objects can’t be seen sharply; corrected w/neg. lenses which diverge light before they enter the eye |
| Hyperopia- farsightedness | common condition in which light entering the eye is focused behind the retina; corrected w/pos. lenses which converge light before they enter the eye |
| Astigmatism | visual defect caused by unequal curving of one or more of the refractive surfaces of the eye usually the cornea; vertical lines focused in front of the retina & horizontal lines focused in front of retina (vice-versa) |
| Adult human eye is | 24 mm long |
| Transduced | referring to the conversion from one form of energy (e.g. light) to another (e.g. electricity); conversion of light into neural energy when light enters the retina that can be interpreted by the brain |
| Fundus | back layer of the retina--- what the eye doctor sees through an opthalmoscope |
| Optic disc | a white circle in the fundus where the arteries & veins that feed the retina enter the eye & where the axons of ganglion cells leave the eye via the optic nerve. Has no photoreceptors (blindspot) |
| Photoreceptors | light-sensitive receptors in the retina; stimulate bipolar, horizontal & amacrine cells (neurons) which connect to ganglion cells whose axons pass through the optic nerve to the brain |
| Rods | photoreceptors specialized for night vision; approx. 90 million & function under conditions of dim (scotopic) illumination |
| Cones | photoreceptors specialized for daylight vision, fine visual acuity, & color; approx. 4-5 million & concentrated in centre of fovea; function best in bright (photopic) illumination |
| Duplex | consisting of 2 parts: the rods & cones which operate under different conditions |
| Outer segment | part of a photoreceptor that lies b/w the outer segment & the cell nucleus; adjacent to pigment epithelium; stores visual pigments & incorporated into the membrane |
| Inner segment | part of a photoreceptor that lies b/w the outer segment & the cell nucleus; visual pigments are made here |
| Synaptic terminal | location where axons terminate at the synapse for transmission of information by release of a chemical transmitter |
| Chromophore | light-catching part of the visual pigment of the retina |
| Rhodopsin | visual pigment found in rods |
| Retina has 5 major classes of neurons | (1) photoreceptors (2) horizontal cells (3)bipolar cells (4) amacrine cells (5) ganglion cells |
| Visual pigments | consist of a protein (an opsin), the structure of which determines which wavelengths of light they absorb |
| Third photoreceptor ? | lives among the ganglion cells & that is involved in adjusting our biological rhythms to match the day & night of the external world |
| Photoactivation | activation by light; light into the outer segment of a rod & is absorbed by a molecule of rhodopsin, it transfers its energy to the chromophore portion of the visual pigment molecule (p.37) |
| Hyperpolarization | an increase in membrane potential where the inner membrane surface becomes negative than the outer membrane surface (p. 37) |
| Graded potential | an electrical potential that can vary continuously in amplitude |
| Eccentricity | distance b/w the retinal image and the fovea |
| Fovea | has high acuity and used to identify objects to read, & to inspect fine detail; use the periphery to detect & localize stimuli that we aren’t directly looking at (looking out from the “corner of the eye”) |
| Short wavelength sensitive cones (S-cones) | constitute only about 5-10% of the total cone pop. & are missing from the center of the fovea |
| Long wavelength sensitive cones & medium wavelength sensitive cones | twice as many L-cones as M-cones; the ratio of L- to M-cones varies enormously among individuals |
| Horizontal cells | specialized retinal cells that contact both photoreceptor & bipolar cells; run perpendicular to photoreceptors |
| Lateral inhibition | antagonistic neural interaction b/w adjacent regions of the retina; lateral connections formed by horizontal cells & photoreceptors is imp. to perception |
| Amacrine cells | retinal cells found in the inner synaptic layer that make synaptic contacts w/ bipolar cells, ganglion cells, & one another; receive input frm bipolar & amacrine cells & send signals to bipolar, amacrine, & retinal ganglion cells |
| Bipolar cells | retinal cells that synapse with either rods or cones (not both) & w/ horizontal cells, & then pass the signals onto ganglion cells |
| Diffuse bipolar cells | bipolar retinal cells whose processes are spread out to receive input from multiple cones;characteristic of the rod pathway & same sort of convergence occurs in the cone pathway in the peripheral retina |
| Sensitivity | (1) ability to perceive via the sense organs (2) extreme responsiveness to radiation, especially to light of a specific wavelength (3) ability to respond to transmitted signals |
| Visual acuity | measure of the finest detail that can be resolved by the eyes |
| Midget bipolar cells | small cone bipolar cells in the central retina that receive input from a single cone & pass it to single ganglion cell (P ganglion cells) |
| temporal sensitivity | detection of changes in light patterns over time |
| ON bipolar cells | bipolar cells that respond to an INCREASE in light captured by the cones |
| OFF bipolar cells | bipolar cells that respond to a DECREASE in light captured by the cones |
| Ganglion cells | retinal cells that receive visual info. from photoreceptors via 2 intermediate neuron types (bipolar cells & amacrine cells) & transmit info. to the brain and the midbrain; send msgs thru axons which gather @ the back of retina & known as optic nerve |
| P ganglion cells | small ganglion cells that receive excitatory input from single MIDGET bipolar cells in the central retina and feed the PARVOCELLULAR layer of the lateral geniculate nucleus; 70% *ganglion cells in human retina |
| M ganglion cells | ganglion cells resembling little umbrellas that receive excitatory input from DIFFUSE bipolar cells & feed MAGNOCELLULAR layer of the lateral geniculate nucleus; approx. 8-10% * ganglion cells in human retina |
| Receptive field | the region of the retina in which visual stimuli influence a neuron’s firing rate; influence can either be excitatory or inhibitory which increase or decrease the ganglion’s firing rate respectively |
| Stephen Kuffler | 1st mapped the receptive fields of individual retinal ganglion cells in the cat using small spots of light (42) |
| Kuffler’s discovery | spatial layout of the ganglion cell’s receptive field is essentially concentric; that is a small circular area in the center responds to INCREASE in illumination & surrounding annulus area responds to DECREASE in illumination |
| Ganglion cell | fires the fastest when the spot size matches the size * the excitatory center & reduces its firing rate when the spot begins to encroach on its inhibitory surround |
| Ernst Mach | Austrian physicist whose name is attached to units of sound; famous for Mach bands |
| Mach Bands (a) | visual illusion gets its name from the illusory bright stripe in the region marked B and illusory dark stripe marked D |
| Mach Bands (b) | actual intensity distribution of the Mach pattern illustrates a luminance ramp edge. |
| retinitis pigmentosa (RP) | progressive degeneration of the retina that affects night vision & peripheral vision. RP commonly runs in families & can be cause by defects in # of diff. genes that have been recently identified |
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Ugly.Beauty
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