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PSYB51 Ch1-4 (Midterm1).docx

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University of Toronto Scarborough
Matthias Niemeier

PSYB51 MIDTERM # 1 CHAPTER 1  Perception + reality are products of evolution - Survival/importance of type of energy in the environment determines which senses have developed/may not see entire reality but we see what is important to our survival  Plato - Reality/perception is dependant on info gathered by our senses - understanding of reality is restricted to things we can perceive - forgot aspect of learning (added by Heraclitus) - truest sense of reality comes from people’s minds and souls (not from body) - Nativism= idea that mind produces ideas that are not derived from external source  knowledge is born with you  Descartes - Dualist view of the world both mind and body exist - mind-body dualism= the idea positing the existence of 2 distinct principles of being in the universe: spirit/soul and matter/body  Heraclitus - Can never step into the same river twice “panta rhei”= everything flows - Idea that perceiver cannot perceive the same thing twice in exactly the same manner experience/learning adaptation alters perception change (we pick out things at change and adapt to things that are constant)  Democritus - World is made up of colliding atoms sensations caused by atoms leaving object and interacting with our sense organs perception= result of physical interaction between world and our bodies - *true until today sensory transducers= physical energy to neural energy (hair in cochlea, taste-buds, retina in eyes)  Hobbes - Believed that everything that could ever be known/imagined had to be learned through our senses  Locke - Sought to explain how all thoughts, even complex ones, could be constructed from experience with a collection of sensations  Fechner - Invented PSYCHOPHYSICS and theory of PANPSYCHISM, thought to be the true founder of experimental psychology - Followed up Weber’s work on Weber’s laws/fractions  Adaptation: (Heraclitus) a reduction in response caused by prior or continuing stimulation - Ex. Looking at male/female faces and a hybrid, you perceive the hybrid as the opposite of what you were primed with because you pick out change= OPPOSING ORGANIZATIONS - Ex. Primed with rat, you see a rat/ primed with man, you see a man due to learning  Monism (opposite of dualism/Descartes)= mind and matter are formed from/reduced to a single ultimate substance or principal of being just mind or just matter - Materialism= type of monism=physical matter is the only reality and everything including the mind can be explained in terms of matter and physical phenomena  Empiricism (opposite of Nativism/Plato)= the idea that experience form the senses is the only source of knowledge not born with knowledge, learn from your senses  Reality= in btwn Nativism (Plato) and Empiricism born with and gradually learn knowledge  Panpsychism (Fechner)= idea that all matter has consciousness  Psychophysics (Fechner)= science of defining quantitative relationships btwn physical and psychological (subjective) events  Weber’s Law= smallest CHANGE in a stimulus, such as weight of an object, that can be detected is a constant proportion of the stimulus level - (delta)I= kI - delta I= JND/difference threshold, k= Weber fraction, I=stimulus level - JND= smallest detectable difference btwn 2 stimuli, minimum change in stimuli that can be correctly judged from the reference stimuli two-point threshold: minimum distance at which 2 stimuli can be distinguished (different depending on size of somatosensory cortex, Ex. Finger/shoulder)  Fechner’s Law: principle describing the relationship btwn stimulus magnitude and resulting sensation magnitude such that the magnitude of subjective sensation increases proportionally to the logarithm of the stimulus intensity (S increases less quickly than R) - S= k log R - S= psychological sensation, k=constant, R=physical stimulus level  Stevens’ Law: principle describing the relationship between stimlus magnitude and resulting sensation magnitude such that magnitude of subjective sensation is proportional to stimulus magnitude raised to an exponent - Expansion of Fechner’s law as there were some exceptions (Ex. Electric shock) - S=aI^b - S=sensation, I= stimulus intensity, b=exponent, a= constant - Used magnitude estimation to formulate graph - Exponent of 1 sensation and stimulus intensity rise proportionally, exponent of <1 S rises slower than I, exponent of >1S increases faster than I (exception to Fechner’s Law)  Absolute threshold= minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time (Ex. Absolute threshold for emotional experience when do u first detect a smile? Whereas JND would be how different do 2 faces have to be in order to notice the difference)  PSYCHOPHYSICAL METHODS 1. Method of constant stimuli (Fechner) - Many stimuli from rarely to almost always perceivable (or rarely to almost always perceivably different) are presented one at a time. Responses= y/n or same/different. Stimulus levels and responses are graphed and the intensity of the stimulus where it was perceived 50% of the time= absolute threshold. 2. Method of limits (Fechner) - Particular dimension of a stimulus/ difference between two stimuli is varied incrementally until the participant responds differently repeated trials, absolute threshold is line where 50% of the time was responded yes/no 3. Method of adjustment (Fechner) - Method of limits in which subject controls change in stimulus - *decreasing accuracy from 1-3 but increasing efficiency 4. Magnitude estimation - Participants are asked to assign values according to perceived magnitudes of stimuli (better if participant decides scale as well) 5. Cross-modality matching - Similar to magnitude estimation= matching intensities/magnitudes of sensations that come from different modalities  Signal Detection Theory: A psychophysical theory (not method) that quantifies the response of an observer to the presentation of a signal in the presence of noise - Calculate d’ (measures of sensitivity) based on hit/false alarm rates - Interprets the importance of internal noise vs. external noise - Influenced by biases (costs of decisions, probability of events, personality) - For a fixed d’= all you can do is change your pattern of errors by shifting the response criterion (shift to left= no misses, but increased # of false alarms and vice versa)  changing response criterion of a fixed d’= changes hits/false alarms in predictable way  Receiver Operating Characteristic (ROC) curve= in studies of signal detection, the graphical plot of the hit rate as a function of the false alarm rate hits= y axis, false alarm=x axis if hit/false alarm rate is the same= diagonal which means observer can’t tell difference btwn presence and absence of stimuli as the observer sensitivity increases, the curve bows upwards towards the upper left corner (d’ increases). - Upper left corner= perfect ability to distinguish signal from noise  Fourier Analysis= analyses that allow understanding about how complex sounds (music/speech), motions, images etc. can be decomposed into a set of simpler signals - Images= broken down into components (spatial frequencies) that capture how often changes from light to dark occur over a particular region in space -  spatial frequency= # of cycles of a grating per unit of visual space (usually specified in cycles per degree= # of pairs of light/dark bars per degree (size of a thumbnail at arms length) of visual angle - find that many individual neurons have strong preferences for frequency components  MULLER - Doctrine of specific nerve energies= states nature of a sensation depends not on HOW a nerve is stimulated but on WHICH sensory fibers are stimulated (Ex. Pressing on closed eye produces visual image even without light) - Not limited to cranial nerves= Ex. Capsaicin= chemical causes warmth fibers in skin to fire creating sense of heat despite stable temperature/ opposite for menthol= both can cause pain sensation if in high quanitity - Believed we are only aware of the activity of our nerves and we cannot be directly aware of the world itself - Vitalism- belief that special vital forces drive living organisms  HELMHOLTZ - Didn’t agree with vitalism thought brain + behavior should follow/ be explained by physical forces (vitalism violated law of conservation of energy) - Showed that activity of neurons obeys normal rules of physics/chemistry - First to effectively show how fast neurons transmit their signals time passes btwn when u stub your toe and when you feel itnot all neurons transmit at equal speeds (challenges vitalism)  Cranial Nerves (12 pairs) 1. Olfactory Nerves (#1)- smell (olfactory epithelia in nose olfactory bulb 2. Optic Nerve (#2)- vision (ganglion axons of retinaV1  brain) 3. Occulomotor Nerve (#3), Trochlear Nerve (#4) and Abducens Nerve (#6)= control muscles that move the eye 4. Vestibularcochlear/Auditory Nerve (#8)- connect inner ear with brain  Neurotransmitter- chemical substance used in neural communication at synapes (previously believed neural communication was all electrical signales) psychoactive drugs work by inc/dec effectiveness of these  Hodgken-Huxley Cycle: electrochemical process involving Na+ moving into the neuron, and K+ moving out via voltage-gated channels causing neurons to fire in all or none fashion  Entire populations of neurons work in concert to process info  Electroencephalography (EEG)= using electrodes on the scalp, measures electrical activity from populations (not individ) of many neurons in the brain roughly localize whole populations of neurons, and to measure their activities with TEMPORAL accuracy single behavioral measurement isn’t very informative, so many measurements are made and averaged  Event-Related Potential (ERP)= measure of electrical activity from a subpopulation of neurons in response to particular stimuli that is a resulted averaged waveform from may EEG recordings tells us about timing of nervous system responses to stimuli  Magnetoencephalography (MEG)= similar to EEG, measures changes in magnetic activity across populations of many neurons in the brain maintains good measure of timing with better localization more expensive  Computed tomography (CT)= standard x-rays used to form 3D images  Magnetic resonance imaging (MRI)= imaging technology that uses responses of atoms to strong magnetic field to form images of structures deals with the presence of H (or water) to see water-rich tissue in your head  Functional magnetic resonance imaging(fMRI)= most important MRI for study of senses shows activity of living brain through BOLD (blood-oxygen level dependant signal= ratio of oxygenated to deoxygenated blood) instead of looking for presence of water, looks for evidence for demand of more resources Drawback: takes a few seconds for BOLD signal to rise after a bit of the brain becomes active so temporal resolution isn’t s good as EEG/ERP and is also loud BUT makes it possible to measure localized patterns of activity in the brain results superimposed on MRI of the brain CHAPTER 2  Light= wave/stream of photons (tiny particles consisting of ONE quantum of energy) wavelength of visible light= 400 to 700 nm Violet=400nm, Red=650 nm can sense heat for example from other wavelengths  Light can be: - Absorbed: taken up and transformed into other forms of energy (Ex. Solar panel= light energy to electrical energy) - Transmitted= opposite of absorption= convey light from one place to another through a transparent medium (through optic filter) - Scatter= to disperse light in an irregular fashion - Reflected= energy that is redirected when it strikes a surface= not absorbed or transmitted= Purkinje reflections (light bounces of eyes in 4 reflections sclera + lens)= most light surfaces reflect majority of light which is what makes them look lightly colored - Diffracted= Bent or having waves that are spread out (waves of sound or light as they encounter an obstacle/ pass through a narrow aperture) - Refracted: energy whose course is altered as it passes into another medium (ex. Light entering water from air= difference in densities, rainbows) light is refracted in the cornea, lens, aqueous + vitreous fluids of our eyes  Sensing light is important for survival edible foods, view dangers/predators from a distance, social cues, circadian rhythms, trees to change color/adaptation mechanisms etc.  Evolution of the eye: eye spots with light sensitive protein opsin on flat surfaces with photoreceptors= simply region of photosensitive cells depressed/folded area forming cavity with photoreceptor allows more spatial sense (where does light hit and where it doesn’t) PINHOLE eye with water filled chamber allows finer directional sensitivity= smaller hole/ but downside is very little light enters so low contrast, there is no refraction transparent humor develops in an enclosed chamber which is more hygienic as nothing can enter but light distinct lens and flat cornea develops so pinhole can be larger/smaller iris and cornea develop so the spherical cornea helps with refraction (more power than lens)  Summary: region of photosensitive cells cavity pinhole with water chamber enclosed chamber with transparent humor distinct lens and flat cornea iris and spherical cornea EYE ANATOMY  Cornea= transparent window into the eyeball most light photons are transmitted through not absorbed or refleted but MAXIMUM refraction power no blood vessels because blood would absorb light rich supply of transparent nerve endings in case of damage form tears and close eye  Aqueous humor= fluid derived from blood, fills space immediately behind cornea and removes waste while supplying Ox and nutrients to cornea and lens watery fluid with refracting power  Crystalline lens= lens inside eye that enables changing of focus, connected to zonules of zinn and then the ciliary muscles ACCOMODATION: change in focus of lens altering its refractory power to focus light rays (ciliary muscles contract, zonules of zinn relax and lens bulges OR ciliary muscles relax, zonules of zinn pull and lens is flat) flatter lens allows for distant vision, blulged lens allows for closer/nearer vision  Pupil= dark circular opening at centre of iris where light enters the eye controls amount of light reaching the retina via pupillary light reflex  Iris= colored part of the eyes, muscle that expands and contracts the pupil  Vitreous humor= transparent fluid (egg-white) that fills vitreous chamber in posterior part of the eyes 80% internal volume of eye last refracting power  Retina= light-sensitive membrane in back of eye containing rod/cone photoreceptors fovea= depression in retina, surrounded by macula (dark spot in fundus view)= no blood vessels in fovea to prevent interference  *much light is lost in space/atmosphere because of absorption and scattering (1/2 light reaches from cornea to retina)  optic disk= where arteries and veins that feed the retina enter the eye, and where ganglion cells leave the eye via the optic nerve blind spot (different for different people)  compensate because 2 eyes, fill in the gaps for each other  Problems with Refraction: - Emmentropia= normal refraction refractive power=length of eye - Myopia= eyeball is too long for optical components image focused in front of the retina nearsightedness (can’t see distant objects), negative lens - Hyperopia= eyeball is too short for optical components (babies) image focused behind the reina farsightedness (can’t see near objects), positive lens - Eyes generally grow to match the power of optical components - Astigmatism= visual defect caused by unequal curving of one or more of the eyes refractive surfaces (usually cornea is not spherical)  5 classes of cells in the retina 1. Photoreceptors= neurons that capture light + initiate the act of seeing by producing chemical signals (transducers) light-sensitive receptor  photoactivation (activation by light)  can pass GRADED potentials unlike other neurons (vary continuously in amplitude due to possible hyperpolerization which is when inner membrane surface is more electronegative than outer) VERTICAL PATHWAY duplex retina: a. Cones (4-5 mil)= larger, more tightly packed in foveal centre (rod-free area) but density drops with retinal eccentricity (distance from fovea) 3 types of pigments: S (not found in fovea so fovea is essentially dichromatic), M, L differ in accepted wavelengths and therefore color visual acuity (low sensitivity and color processing PHOTOPIC VISION b. Rods (90 mil.)= contain Rhodopsin pigment nighttime vision (no rods in fovea, so only peripheral vision at night, low acuity, high sensitivty) SCOTOPIC VISION c. 3 photoreceptor for circadian rhythm melanopsin (sensitive to ambient light) d. *check graph for distribution of rods/cones e. *trade-off between acuity and sensitivity f. visual pigment in rods/cones= 2 parts, Protein opsin structure determines wavelengths of accepted light and chromophore which captures light pigments made in internal segment but stored in membranous discs of outer segment 2. Horizontal Cells= perpendicular to photoreceptors, making contact with multiple nearby photoreceptors implicated in the lateral pathway: interacting via lateral inhibition (antagonistic neural interaction btwn adjacent regions of the retina) 3. Amacrine cells= part of lateral pathway, also perpendicular to photoreceptors receive input from bipolar cells and other amacrine cells and send signals to biopolar, amacrine and ganglion cells 4. Bipolar cells= VERTICAL PATHWAY vertical cells that synapse with either rods or cones (NOT BOTH) and pass the signal to ganglion cells cellular intermediaries a. Diffuse bipolar cells: receive input from multiple photoreceptors (RODS + PERIPHERAL CONES)= CONVERGENCE increase sensitivity (see in dim light environments) but decrease acuity (so one strip of bright light is the same as multiple strips of dim light) b. Midget bipolar cells: receive input from a single cone in the fovea (each cone connects to two bipolar cells)= DIVERGENCE c. ON bipolar cells: respond to an increase in light captured by cones d. OFF bipolar cell: responds to decrease in light captured by cones e. DIVERGENCE each foveal cone connects to one ON bipolar cell and one OFF bipolar cell 5. Ganglion cells= retinal cells that receive visual info from photoreceptors via either bipolar or amacrine intermediaries VERTICAL pathway final layer of retina pass info to brain  axons gather to form part of the optic nerve can fire action potentials even in absence of visual stimulation receptive field= region in space/retina in particular for ganglion cells in which stimuli will activate a neuron (inhibitory or excitatory effect) spatial layout of retinal ganglion RF is COCENTRIC (off center/on center cell, fire most rapidly when size of spot of light matches the center exactly) function as filter (respond best to spots of a particular size and less to smaller/biggers ones) MOST sensitive to CONTRAST differences not to average intensity of light so view things the same despite lighting conditions Example of MACH BANDS= lateral interaction in the retina, neuron in middle transition has more surround antagonism so will appear darker or lighter a. P ganglion cell= small ganglion cell that receives excitatory input from single midget bipolar cells in the central retina and feeds the parvocellular layer of the LGN (1 cone photoreceptor in fovea midget bipolar cell in central retinaP ganglion cell parvocellular layer of the LGN)= smaller RF, finer spatial resolution/acuity, sustained responses, sensitive to colour= 70% of ganglion cells sustained responses because signal contrast not change over time b. M ganglion cell= a ganglion cell resembling an umbrella that receives excitatory input from diffuse bipolar cells and feeds the magnocellular layer of the LGN (rods/peripheral cones diffuse bipolar cell (convergence) M ganglion cell magnocellular layer of the LGN)= larger RF, coarser spatial resolution/acuity, transient responses, insensitive to colour= 8-10% of ganglion cells transient responses because signal info about how an image CHANGES over time, with a constant stimuli they return to spontaneous rate c. Koniocellular cell= neuron located between magnocelluar and parvocellular layers of the LGN (koniocellular layer of LGN)  Dark/Light Adaptations 1. Pupil Dilation - amount of light entering the eye is proportional to the area of the pupil, which is controlled by the iris muscles 4 fold change in pupil diameter (2 to 8mm) can result in a 16 fold improvement in sensitivity 2. Photoreceptors - Human’s duplex retinas Rods provide a lot of sensitivity at low light levels, but become overwhelmed when background becomes moderately bright loss in info quality cones much less sensitive than rods but operating range is much larger (10 to 100 to 1000 photons per second) after adapting to bright light= cones recover sensitivity very quickly and then saturate after adapting to low light= rods recover slowly but after 30 mins are very sensitive to dim light 3. Photopigment Replacement - Dim lighting condition= plently of photopigment available and rods and cones respond to as many photons as they can rod system is capable of detecting a single quantum of light! - After a photopigment is used to detect a photon (bleached) it must regenerate before it can work again slow regeneration= means in less light all photons are used which increases sensitivity, but in high light some photons are thrown out and others are used 4. Neural Circuitry of the Retina - Accounts for why we are not bothered by variations in overall light levels visual system regulates amount of light entering the eye by ignoring whatever variation in overall light level is left over cells will still fire at an above spontaneous rate when light falls on the entire receptive field as long as light is brighter on the ON portion than off portion as long as ganglion cells are not FULLY saturated= they will encode pattern of relative light/dark in retinal image pattern of illumination NOT overall light level= primary concern 5. SUMMARY of DARK ADAPTATION: how does visual system deal with variations in overall light level? First, reduce scale of problem by regulating amount of light entering eye (pupil dilation) then by using different photoreceptors in different situations (rods/cones) then by effectively throwing away photons we don’t need (photopigment bleaching) lastly by responding to contrast between adjacent neural regions= ganglions do their best to ignore variation in overall light level  Problems with Vision - MAN WHO COULDN’T SEE THE STARS= Retinitis Pigmentosa: family of hereditary diseases that involve the progressive death of photoreceptors and degeneration of the pigment epithelium commonly rods affected first so problems with nighttime + peripheral vision eventually spreads to fovea leading to total blindness age of onset/rate of progression varies complex variations of the genetics but recently due to human genome mapping= identified some implicated genes view of fundus: conspicuous clumps in the retinitis pigmentosa fundus that have a characteristic shape= BONE SPICULES 40-60% OF VF is impaired - Cataracts: opacity (loss of transparency of lens that are usually transparent because the crsytallins proteins that form is are packed very densely and regularly) of lens due to irregularities of the crystalins interfere with vision because they absorb/scatter more light than normal lens - Heteronymous: different visual field defects for the two eyes (heteronymous= lesion of optic chiasm, tumour in the hypothalamus, both temporal sides of vf is blind)
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