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Midterm

Sensation and Perception Midterm 2

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Department
Psychology
Course
PSYC 2390
Professor
Naseem Al- Aidroos
Semester
Winter

Description
webers law= difference threshold, dl/s=k stevens power law, magnitude estimation, p=ksto the power of n response compression: stimulus intensity is higher than percieved (exponent less than 1) response expansion: stimulus intensity is lower than percieved (exponent higher than 1) Visual search: find one stimulus amoung many as fast as possible Info can be passed within or between neurons -if passed within, the exchange is all electrical (change in potentials) -electricity in the brain: energy resulting from charged particles, (neg moving towards positive, vise versa) Charged molecules called IONS (positive is cations and negative is anions) -two types that play important role of electrical ions within axon: sodium ions (Na+), and potassium (more inside, k+) -organic anions (protiens) that have negative charges and are found inside the cell, they cause the stron negative charge to create a negative potential within the cell -resting potential of a neuron is -70 mV (millavolts) aka the inside of the cell is about 70 mV more negative on the inside than outsideAT REST, and this is a measurable electrical potential -microelectrode setup used to measure this potential -information is passed within a neuron by CHANGING this potential, polarization changes Action Potential -This process is called changing the action potential: -when part of an axon depolarizes, eg potential becomes slightly less than -70 that is the signal that that segment of the axon needs to be transmitted to the next cell -high concentration of sodium inside, but usually cant escape -voltage activated ion channels open and allow sodium to push its way into the cell -as soon as the axon becomes depolarizes the channel opens and ions diffuse, which means the next segment if axon becomes more positive and then the cycle continues down the length of the axon -AKAdepolarization-->ion channels open--->sodium rushes into cell, which depolarized next section of axon -this sequence is called the action potential (happens through depolarization that triggers sodium channels, we sometimes call them SPIKES in electrical activity. --after action potential, there is an imbalance and we need to get back to balance -to do this, the sodium channels close and potassium channels open which go from inside the cell to outside the cell -KNOW STAGES : resting, depolarization, re-polarize, hyper-polarize, back to resting Nerve Impulses All or none Law: The amplitude and velocity of an action potential are independent of the intensity of the stimulus that initiated it. This means that a stronger stimulus would not cause a different action potential. When you get it, you get it, always the same Rate-law: stimulus intensity instead is transmitted based on the rate of generation of action potentials, basically the frequency at which they occur. You need to look at an acion potential over time in order to understand a stimuli intensity Info moving from cell to another cell: Eventually the info passing inside cell will come to an end, at the end of this cell is a synapse -the transition between these is synaptic transmission, and this si a chemical, rather than electrical transmission -presynaptic is cell sending info, postsynaptic is the one recieving the information-the end of presynaptic terminal in axon is filled with sacs called vesicles which contain neurotranmitters (chemicals) . Chemicals are released into gaps -there are receptors sites on post synaptic, and if the site matches the neurotransmitter it triggers voltage change in postsynaaptic cell -nuearotransmitters bind with sites on receptor cell, we get a change in voltage of the dendrites -different kindas of chemicals can be released to recieving cell which causes it to become either more negative or more positive -Excitatory transmitters-cause depolarization (neuron becomes more positiveand increases the likelihood of an action potentialsInhibitory transmitters- cause hyperpolarization, the neuron becomes more negative and this DECREASES the likelihood of action potential -Regardless, the chnage in polarity will spread through axon Ho to taste salt? Sensory receptor on surface of tongue(it isnt naturally sodium full) you eat salt that dissolves into sodium, the sodium is passed from cells to neurons through sodium ions channels, travels down axons and causes Introduction to vision: -when you have incoming info that is excitatory, the frequency of action potentials increases, vise versa for inhibitory -however, at rest there is a baseline of occasional spontanious action potentials, which iil increase with excitatory and decrease with inhibitory -Neural Circuits -Groups of neurons connected by excitatory and inhibitory synpases -the behaviour of a circuit is governed by: 1) the pattern of its connections, and whether its excitittory of inhibitory -visual example: in the back fo our eyeballs there is photoreceptors that detect light -stimulate one photoreceptor, it excites cell B which causes it to increase rate of action potentials -the more we stikmulate more photoreceptors, there is not increase in level of excitation in cell B, it is the same level as if wee JUST stimulate photoreceptor 4 -convergance is when multiple recpetors combine and send info to a single postsynaptic cell -since only one photoreceptor effect cell b, there is NO convergence -in a more complex version, all of the photoreeptors can converge onto cell B -in this case, if you stimulate photoreceptors 3-5, there is a summate of the excititory signals causing agreater change in postsynaptic firing rate, therefore fires three times more -therefore, the more photoreceptors excited, the greater the firing rate within this cell -this is a convergent circuit -in a different circuit, some of the connections can be inhibitory. This has a diferent effect on behaviour of cell b in response to diff kinds of light -is receptors 1 and 2 become activated, they inhibit firing rate (same with 6 and 7) -firing rateof cell B will start to decrease once inhibitory signals occur receptive field: the set of all sensory receptors that affect the cell, also spimplifies description by ignoring intervening connections : three types of circuits: simple (photoreceptor 4), excititory (1-7) and excititory/inhibitory (1-7) Spatiotopic organization od sensory receptors in the eye : -sheet of visual sensory recoetors is called retina (the receptors are spatially organized) -many early neurons exhibit center-surround receptive field (which is and excititiry-center-inhibitory surround (like earlier when the middle three exhibit excititory and the outside exhibit inhibitory OR inhiitory- center- excititory surround Later stages of visual processing (cells further away from lreceptors) eventually it becomes impossible ot distinguish between stimuliand behaviour of cell -modern definition of receoptive field: -types of stimuli that affect the response of a neuron could refer to : 3d volume , feature, catagories What is sensory code? 1)specificity coding: the idea that any one single neuron may be associated with one specific stimulus, “granmother cell”, if only fires when youre looking at your grandmother 2) distributed coding: idea that individual stimuli arent recognized by a single neuron, but rather a pattern of firing across many neurons, eg several neurons fire but some more strongly than others 3) sparse coding: only a relatively small number of neurons are neccessary, but you do need to look at all of the ones it doooes activate (this is like a midpoint between specificty and distributed coding. Chapter 3: Light and the eyes: Four basic properties of light: 1)Light is a type of energy composed of tiny particles called photons, this is the type of energy we are going to sense -it travels about 300000 km/s -light is both a particle and a wave 2) Every photon has a wavelength -produces electromagnetic field which gets stronger and weaker , distance travelled during one complete cycle is the wavelength (one complete cycle of a photon), each photon can have different wavelengths. Most of the wavelengths are visible to us, few arent really long waves (radio) really short waves (radiation) 400-700 nanometres is the visible waves, these are the ones we recieve in different colours . If it is 700 nanometeres you will see it as red for example. 3) Light can vary in intensty, which it ultiatly how many photons there are in the light, if that spread of photons is spread out over space or time it will be dimmer---> intensity= # of photons / area x duration 4) Photons travel in straight lines, unless reflected, absorbed or refracted by matter. When they run into something they will reflect . Green paper will absorb all wave lengths (colours) except green, so we see green) , visual system uses light reflected off objects to make inferences about object Refraction: when light passes into an object the angle of the light changes, this change is greater for shorter wavelengths. Eg prisms How the eye focuses light: cricitcal parts of eye: -sclera: white membrane on outside of eye -cornea is the translucent part of the memberane at the front, where light passes through, it is slightly curved which effects refraction, plays important role in focusing light -iris: coloured part of light, contricts and dialates to make pupil bigger or smaller pupil: just a hole that allows light through-lens: behind pupil, disc that can be changed a bit, around the edges of the disk are muscles called.. – ciliary muscles, when these muscles contract it changes to shape of the lens, this allows us to refract more and focus on different things -retina: photoreceptors are sheet at back of eye, little pit called fovea: this is the pit in retina where you get most clear processing – -information from receptors fire neruons through optic nerves.As a consequence you dont see info in the small spot where the retina meet optic nerve (blind spot) Focusisng on images: -goal is all of the light off of an image to hit single point on retina -the distance an opbject is from you effects how important it is to focus light. -when an object is relly close to your ppil, light can actually pass through pupil at many diff angles. Thus, if you get more than 20 feet away from eyeball light enters through one direction, therefore the eyeball can focus all of that light on the back of the eyeball, the naturual shape of the eyeball -objects less than 20 feet , the point at which light is to be focused changes , the light then hit behind the retina. This is when we need to change the shape ofthe length that will make light hit the retina Cilliary Muscles: naturual state is relaxed, the lens is held by zonule fibers that are very taunt. However when the ciliary muscles contract, some of the tension is released thus the lens gets smaller and thicker which bring focus point forwared in the eyeball When cilliary musckes reeach max constiction it is called Near point, the distance at which you can not focus , this point gets further and further away from our eyes as we get olfder,mostly beause muscles get weaker and lens becomes less flexible presbyopia is what this old age does to the eye, in order to overcome this you need lenses eg redeading glasses If the lens is too short and fat when relaxed, objects that are more than 20 feet away cant be focused because light will hit closer to the centre of the eye, called myopiaB or near sightedness (almost like it is accomidating when you dont need to) axial mypoia- eyeball is to long hyperopia or farsightenness: challnege is that you have to accomadate for both long distances and short distance focussing, this happens when the lens and or cornia is too long/thin when relaxed Opsin-protein flds seven times through membrane, atached to this is photosensitive molectule called retinal (this is the place where the retinal is a single molecule attached to opsin and the opsin fold through -ypsychophysisists have perforemd test of “absolute threshold” the test how much photons need to be stimulated to create an action potential , turns out oyu inly need ONE proton -Hecht's psychophysical experiments cnfirmed that a single isomerization is sufficient to activate receptor, seven active rods needed to consciously see light Rods vs Cones: four physical differences: 1)distribution on retina 2)rate of visual pigment regeneration 3)spectral sensisitivy/absorbtion 4)neural connectivitiy These all result in diff behavioural responses. Rods: Fast responsees to smalll amounts oof light int he peripheral visio. Good for night vision. No colour and low acuity Cones: cponvery colour info, high acuity especially in centr eof retina (fove a), but require more light and have slower responses 1) distribution: light directly infront of you will strike fovea, thius has the largest number of densly packed cones, but no rods. This part gives us high spatial resolution. The other cells are also pushed to the side. Causing a pit in which light only passes to rods light in your peripheral view will strike to either side of the fovea. -more rods than conees (120 million rods, 5 million cones) -blind spopt: place where optic nerve leaves eye, we dont notice becauseone eye corrects for other, its loacted at edge of visual field, and the brain fills the spot Rods: good at processing in low light, but not great info, cones good spatial resolution and need high lights. Diseases that effect retina: Macular Degeneration -fovea and small surrounding area are destroyed -created blind spot ON retina -common in older individuals Retinitis pigmentosa: -genetic disease -rods are destroyed first -foveal cones can also be attacked -effects periphery, severe cases can cauase blindness 2. Rate of visual pigment regeneration -dark adaptation: (better at seeing things in dark after time), your pupils dialates and expands to alllow more light into your eye -photoreceptors become more sensitive psychophysics ccan be used to easure changes in light sensitivity over time when theyre observing light over time -after itme even a very faint loight can be detected -the rods and the cones each have their own adaptation curves Measuring dark adaptation: -experiment for cone adaptation: direct light straight into fovia, and changes will be dependent of cone sensivity and independent of rod. Sensitivity increases for three-four mins thenstops -cones change first but then plateu – whenr looking at subjects that only have rods in retinas, dont have cones – -although initially cones are more sensitvie than rods, it switches and rods eventually pass over and become more sensitive than cones. Therefore after about four mins you are using your rods rather than cones - this is why you only really see black and white when you are in the dark -SO how does this take place? -in cones the visual pgment regeneration happens quickly, rods more slowly -psychophysical dark adaptation curvesmatch rates of visualpigment regeneration of rods and cones -visual pigment of regeneration is when the retinal molecule changes shape (osomisized), then a little bit of the opsin molescule bleaches. If there is light, the retinal and opsin must recombine to respond to light -cone regenerates in six minuites -rod pigment regenerates in over 30 min. -BASICALLY we are studying how quickly the retina will become red over time ?(no longer bleached) 3. Spectral sensitivity/absorbtion - Beyond differences in how bright a light is, we can also ask are rods and cones differentially sensitive to waves lengths of light? - THEYARE! Many frequencies are invisible such as ultraviolet or infrared wavelengths - sensitivity also varies within the visual spectrum too -read text to see chart about rods and cones and wavelengths -cones are really good at yellow/green but not great at red -rods are reallty good at blue and green -this can also be examined using physiological methods, isolating oen photoreceptor and seeing hwo much is asorbs a certain colour (wavelength) - this kind o fstudy found that tere is 3 kinds of cones, one absorbs indigo(s cones, short waves), one green (m-cones, medium lengths) and one yellowy light (l-conees are long waves) -very few short cones, mostly m and l cones -if we only had one type of cones, we wouldnt be able to tell difference between a dim grena dn bright yellow light 4. Neural connectivity -how the receptor connects to subsequent neurons in system -vertical communication: receptors, to bipolar cells, to ganglion cells, slightly diff for rods and cones -horizontal communication: amacrine and horizontal cells, pretty similar for both rods and cones – ganglion cells are the ONLY means of getting information out of your eyeball, thus isphtooreceptor doesnt activate a repsonse in a ganglion celll no info is processed – lots ofConvergence of the retina : 126 millions rods and cones – only 1 million ganglion cells – higher convergence of rods than cones, average of 120 rods for each ganglion cells – lower convergence for cones, only average of 6 per ganglion. – In fovia there is a one to one relationship between cones and ganglion cells – The more convergence there is the more sensitivity there is to light, but you also lose the acuity -if ganglion clell requires at least 5 units of light before it reaches action potential and fires, the higher convergence would have higher units of lights (2 x 2 x 2 x 2 x 2) -in cones, since3 there is no convergence, any ganglion cell isn't getting enough accumulation of light therefore doesn't hit threshold for stimulating a response -THEREFORE the reason rods can see better in dimmer light is due to higher rates of convergence – however, the more convergnce there is the harder it is to tell the difference between the sources of light , particularity the spatial difference – because of convergence, you cant tell the difference in spatial from rods because you inly get oine single response in ganglion cell from numourous lights – what is the classical definition of sensory field? The set of sensory receptors that effect and whther they are excitatory or inhiitory. – Ganglion cells getting info from rods have a much larger receptive field than cone ganglion cells - generally, peripheral cells have larger receptive fields than more central/fovela cels (explains high acuity in fovea) Lateral Inhibition of neurons: -Horizontal communication from cells is usually inhibitory -Amacrine cells connect neighbouring cells -basically when on ganglion cell is stimulated, the neighbouring ganglion is inhibited due to lateral inhibition -all ganglion cells recieve some inhibition through neighbouring cells -centre surround ganglion cells are created through later inhibitiom -STRONGEST excitment hen centre is stimulated -Hermand Grid Illusion, you see circles in between squares onyl happens in periphery and not in centre -because each ganglion has centre surround resceptive fields (stimulation tocentre excites, stimulation to inhibirity surround inhibitiry) -cells beside the intersection has lots of excitatorys timulation and only a littlle inhibitory, however the oen in the intersection, we gets lots of centre because its stimulated, but also LOTS on inhibiroty because there is four white pathways that stimulate the surround. -you percieve these intercetions as a decrease in brightness due to the strong activation of inhibitory surround in your periphs -When you looks directly at interceptions, the recpetive fields of all the ganglion cells are completely stimulated therefore there is not difference between the intersection and the middle ganglion cells (they are stimulated in the same way). This causes the illusion to disappear when you look directly at intersection. -Mach Bands: another illusion created due to inhibiroty stimulation the brightest part of stimulus is at far right, however you percieve it to be just past half way. This is created as a consequence of lateral inhibition in the retina -one ganglion cell is 3 quarters in darkness and one quarter lightness. This ganglion cell wont be stimulated as much as the one to the far left.Although the centre one partially fall into light, the light is actually stimulating the inhibiroty surround. The centre is not excited by light, and is also inhibited by light (therefore almost like a negative stimulation) -lateral inhibitions functional purpose is to help you see the edges of things rememmber: ganglion cells are the output from eyeballs, the extent they get excited you percieve light, to the extent theyget inhibited you percieve darkness -the most bright light you see happens when ONLY the excititory sections are stimulated, whereas darkest is when inhibirity rsurround centre is stimulated Visual Cortex and Beyond: From retina, to LGN to cortex optic nerve= big bundle of ganglion axons left half of visual feld primarily stimulates the right half of your eyeball, and right visual field primarily detected by left half of your eyeball -fibres of opitc nerve passs through the optic chiasm, some of the fibres from the left side cross over to the right side, andsome stay (same with right side) -all of the info coming from left sideof field ends up hitting right side of eyeball and going to right hemisphere of brain -thus most info from right visual field processes in left side of brain Processing the Lgn -the first sight in which information goes in the brain -it is the nucleus of the thalmus -LGN have centre-surround receptive fields (same as ganglion cells) – soo their purpose? They not only recive info from retina, but tey also recieve info from higher levels of cortex – SO that means these cells recieve signals both bottom-up(from enviro to brain) and top-down (from brain to enviro) – for every 10 excitatory signals the LGN recieves from retina, aprox. 4 get sent to brain. – Basically it is a regulator that control amount of visual info going into brain – Lgn in both hemispheres – SO: leyers 1,4 and 6 only recieve info from contralateral eye (opposite eye), and 2,3,5 only get info from ipsalateral (from the same side eye) – thus diff eyes project to diff layers – some la
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