Processing the Environment Sensory Perception PDF

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Processing the Environment Sensory Perception...

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Processing the Environment Sensory Perception Visual Cues − Depth, Form, Motion, Constancy − Binocular Cues ● Retinal disparity (eyes are 2.5 inches apart) ● Convergence – things far away, eyes are relaxed. Things close to us, eyes contract. − Monocular Cues ● relative size, interposition (overlap), relative height (things higher are farther away), shading and contour, motion parallax (things farther away move slower) ● Constancy – our perception of object doesn’t change even if it looks different on retina. ♦ Ex. size constancy, shape constancy, color constancy. Sensory Adaptation − Hearing - inner ear muscle: higher noise = contract. − Touch - temperature receptors desensitized − Smell – desensitized to molecules − Proprioception – mice raised upside down would accommodate over time, and flip it over. − Sight – down (ex. Light adaptation, pupils constrict, rods and cones become desensitized to light) and upregulation (dark adaptation, pupils dilate) Weber’s Law − 2 vs. 2.05 lb weight feel the same. − 2 vs. 2.2 lb weight difference would be noticeable. − The threshold at which you’re able to notice a change in any sensation is the just noticeable difference (JND) − So now take 5 lb weight, in this case if you replace by 5.2 weight, might not be noticeable. But if you take a 5.5 lb it is noticeable. − I = intensity of stimulus (2 or 5 lb), delta I = JND (0.2 or 0.5). − Weber’s Law is delta I to intensity is constant, ex. .2/2 = .5/5 = .1. ● Delta I/I = k (Weber’s Law) − If we take Weber’s Law and rearrange it, we can see that it predicts a linear relationship bet − ween incremental threshold and background intensity. ● Delta I = Ik. ● If you plot I against delta I it’s constant

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Absolute threshold of sensation − The minimum intensity of stimulus needed to detect a particular stimulus 50% of the time − At low levels of stimulus, some subjects can detect and some can’t. Also differences in an individual. − Not the same as the difference threshold (JND) – that’s the smallest difference that can be detected 50% of the time. − Absolute threshold can be influenced by a # of factors, ex. Psychological states. ● Expectations ● Experience (how familiar you are with it) ● Motivation ● Alertness − Subliminal stimuli – stimuli below the absolute threshold.

The Vestibular System − Balance and spatial orientation − Focus on inner ear - in particular the semicircular canals (posterior, lateral, and anterior) − Canal is filled with endolymph, and causes it to shift – allows us to detect what direction our head is moving in, and the strength of rotation. − Otolithic organs (utricle and saccule) help us to detect linear acceleration and head positioning. In these are Ca crystals attached to hair cells in viscous gel. If we go from lying down to standing up, they move, and pull on hair cells which triggers AP. − Also contribute to dizziness and vertigo ● Endolymph doesn’t stop spinning the same time as we do, so it continues moving and indicates to brain we’re still moving even when we’ve stopped – results in feeling of dizziness. Signal Detection Theory − Looks at how we make decision under conditions of uncertainty – discerning between important stimuli and unimportant “noise” − At what point can we detect a signal ● Origins in radar – is signal a small fish vs. large whale. ● Its role in psychology – which words on second list were present on first list. ● Real world example – traffic lights. Signal is present or absent (red). Strength of a signal is variable d’, and c is strategy − d’: hit > miss (strong signal), miss neural impulse, by a photoreceptor What is light? − Electromagnetic wave part of a large spectrum − EM spectrum contains everything from gamma rays to AM/FM waves. Visible light is in the middle ● Violet (400nm) – Red (700nm) − The Sun is one of most common sources of light Light enters pupil and goes to retina, which contains rods and cones − There are 120 million rods, for night vision ● Light comes in, goes through pupil, and hits rod. Normally rod is turned on, but when light hits turns off. ● When rod is off, it turns on a bipolar cell, which turns on a retinal ganglion cell, which goes into the optic nerve and enters the brain. − There are 6-7 million cones ● 3 types: red, green, blue ● Almost all cones are centered in fovea Phototransduction Cascade – when light hits rods and cones − Retina is made off a bunch of dif cells – rods and cones. − As soon as light is presented to him, he takes light and converts it to neural impulse. Normally turned on, but when light hits it’s turned off. PTC is set of steps that turn it off. − Inside rod are a lot of disks stacked on top of one another. − A lot of proteins in the disks. One is rhodopsin, a multimeric protein with 7 discs, which contains a small molecule called retinal (11-cis retinal). When light hits, it can hit the retinal, and causes it to change conformation from bent to straight. − When retinal changes shape, rhodopsin changes shape. − That begins this cascade of events – there’s a molecule in green called transducin made of 3 dif parts – alpha, beta, gamma ● Transducin breaks from rhodopsin, and alpha part comes to disk and binds to phosphodiesterase (PDE). ● PDE takes cGMP and converts it to regular GMP. Na+ channels allow Na+ ions to come in, but for this channel to open, need cGMP bound. As cGMP decreases, Na channels closes. ● As less Na+ enters the cell, rods hyperpolarize and turn off. Glutamate is no longer released, and no longer inhibits ON bipolar cells (it’s excitatory to OFF bipolar cells). ● So bipolar cells turn on. This activates retinal ganglion cell which sends signal to optic nerve to brain.

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Photoreceptors (Rods and Cones) − A photoreceptor is a specialized nerve that can take light and convert to neural impulse. − Inside rod are optic discs, which are large membrane bound structures – thousands of them. In membrane of each optic disc are proteins that fire APs to the brain. − Cones are also specialized nerves with same internal structure as rod. − Rods contain rhodopsin, cones have similar protein photopsin. − If light hits a rhodopsin, will trigger the phototransduction cascade. Same process happens in a cone. − Differences: ● 120 M rods vs. 6 million cones. ● Cones are concentrated in the fovea. ● Rods are 1000x more sensitive to light than cones. Better at detecting light – telling us whether light is present, ie. BW vision ● Cones are less sensitive but detect color (60% Red, 30% Green, 10% Blue) ● Rods have slow recovery time, cones have fast recovery time. Takes a while to adjust to dark – rods need to be reactivated. Photoreceptor Distribution in Retina − Where optic nerve connects to retina, blind spot – no cones or rods. − Rods are found mostly in periphery. − Cones are found throughout the fovea, and few in rest of eye. − If we zoom in on fovea – no axons in way of light, so get higher resolution. If light hits periphery, light has to go through bundle of axons and some energy lost. So at fovea light hits cones directly.

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