Summary Sensation and Perception Chapter 1 - 5 PDF

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PSYC 2018

1 Perception Chapter 1 Notes: Introduction

The Perceptual Process

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Stimuli (1-2) o Light is reflected/refracted around the stimuli, crating the principle of transformation which states that the stimuli is transformed between the environment to the percept  This light is further manipulated by the air particles (further objects seem bluer, fog/mist reduces light intensity)  Focused by cornea & lens then is picked up by the retinal receptors (rods/cones)  This creates the principle of representation where the tree is represented on the retina Receptor Processes (3) o Sensory receptors (1) transform environmental energy into electrical energy and (2) shape perception by their response. This is done through visual pigment and transduction o Three pigments (according to the tri-colour theory) respond to different frequencies of light (CONES ONLY) Neural Processing (4) o Neurons (1) transmit signals from receptors to the brain and (2) change/process the signals during transmission (Neural processing)

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o They initially travel to the primary receiving areas (V1 for vision, A1 for audio, in the Occipital lobe and temporal lobe respectively) Behavioural response (5-7) o Electrical signals are transformed into conscious experience (i.e. perception) o Ability to distinguish between perception (the sensory information) and recognition (categorising that information) o Patient Dr. P (in the man who mistook his wife for a hat) suffered from visual form agnosia – an inability to recognise objects. o Finally, Action (7) involves motor activities such as moving towards the object, or moving to react. Knowledge o Knowledge is any information the perceiver brings to the situation. This can be seen by the Man-Rat demonstration – where the perceived image will change meaning dependent on which form (more rat/man-like) is seen first o Bottom-Up Processing refers to processing based on the stimuli reaching the receptors – e.g. seeing a tree o Top-down processing refers to processing that is based on knowledge e.g. recognising that it is a tree  Interactions occur between the two e.g. reading an almost illegible doctors prescription (attempt to make sense, then use knowledge of drug names/prior experience to decipher)

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How to approach the study of perception  Psychophysical approach measures the relationship between stimuli and the behavioural response (stages 1-2 and 5-7) o E.g. experiment to test the oblique effect showing slanted lines and asking for response.  Physiological approach measures stimuli and physiological responses (stages 1-2 and 3-4) o Coppola et al (1998) used Optical brain imaging on ferrets, to measure activity in their visual cortex during a similar oblique effect. They found horizontal/verticle lines created larger brain responses. o Similarly Furmanski et al (2004) did this on humans, finding a larger physiological response of horizontal lines than slanted. Comparing this to the psychophysical response (better detection of horizontal) the perception corresponds with the physiology. Measuring Perception  Thresholds o Absolute threshold = the minimum stimulus intensity that can be detected. o Fechner (1860) proposed three methods for measuring absolute thresholds 1. Method of Limits – the experimenter presents stimuli in ascending or descending order, and the person indicates where the threshold is. 2. Method of adjustment – similar to limits, but the adjustment is performed b the observer (turning a knob to increase/decrease to the perfect amount) 3. Method of constant stimuli – Experimenter presents 5-9 stimuli with different, randomised, intensities. On each intensity the observer mentions if they can/cannot perceive it. – however this is time consuming as it needs many retrials to have a valuable percentage. o Fechner also mentioned the difference threshold (minimum difference between stimuli which is detectable.  The Weber fraction (Weber’s Law) states that the difference threshold is a percentage (around 2% for most senses, yet 8% for light)  Estimating magnitude 11/12/16

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o S. S. Stevens developed scaling/magnitude estimation whereby observers were given a ‘standard’ stimulus and assigns it a value (say 10). They are then presented with different intensities of the stimulus, and are asked to assign a proportional number to it.  Response compression is seen in the graph by light intensity (when the intensity doubles the estimate is less than double) while response expansion is seen by electric shock (when the intensity doubles the estimate is more than double)

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Beyond Thresholds and magnitudes o Phenomenological method is where a person is asked to describe their perception, or when it occurs. (seen in Dr. P) o Visual Search asks observers to find a specific stimulus among many as quickly as possible. (attention/Gestalt) this measures reaction times

Threshold measurement depends on how a person chooses to respond  Person 1 decides: “Say yes at any change, even if I assume it was one”  Person 2 decides: “Only report changes that are clear”  These difference response criterion will produce differing results.

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1 Perception Chapter 2 Notes

Light and Focusing  Visible spectrum between 400-700nm (x10^-9)  Light enters through the pupil and is focused by the cornea  Rods and Cones contain Visual Pigments, which absorb information and trigger electrical signals to pass through the optic nerve  Focusing o Cornea does around 80% of focusing while lens does the other 20%, as it can change shape this adjustment by the Ciliary muscles is called Accommodation. o The point which can no longer be accommodated is called the near point o This ability to accommodate is also lost with age – a condition called Presbyopia – which occurs due to the hardness of the lens increasing. Myopia & Hyperopia  Myopia is near-sightedness, this occurs when the light is focused far in front of the retina and therefore the image comes out blurred. o Refractive Myopia is when it bends light too much o Axial Myopia is when the eyeball is simply too long  Hyperopia is far-sightedness occurring when the image is focused behind the retina, and can be caused by the same reasons. Receptors and Perception  Transduction is the transformation of light energy into electrical energy to pass the information.  Visual pigments have two parts: the small light sensitive region the retinal and the long protein called opsin. o The Retinal goes from being curved to straight, when it is excited by light, this is called isomerization. Adapting to the dark

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Dark Adaptation causes an individuals visual system to become more sensitive when in the dark  The Dark Adaptation Curve shows that rods become much more sensitive in darkness than cones – explaining a loss of colour o Rods take around 20/30 minutes to adjust while cones will take 3 or 4 minutes this difference is due to Visual Pigment Regeneration  Pigment regeneration occurs after the retinal has been exposed to light, separates from the opsin, and is consequently bleached. To become sensitive again the retinal must reconnect.  Rods take over 30 minutes to recover while cones take around 6 minutes. (Rushton 1961) Distribution or Rods & Cones  Fovea contains only cones (around 1% of total), in the centre of the retina.  Peripheral retina includes all the area outside of the fovea, which contains both rods and cones. (Containing 120 million rods and 6 million cones)  Macular degeneration is a process in old age when the fovea is destroyed causing a blind spot 

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Retinitis pigmentosa is a genetic disorder which attacks peripheral cones, and can damage the fovea. Blind spot is a section with no receptors due to the optic nerve endings.

Spectral Sensitivity  Cones are more sensitive to long wavelengths while rods are more sensitive to shorter (both within the 400-700nm range)  The Purkinje shift describes the enhancement of short wavelength perception in the dark  Absorption Spectrum is a plot of the amount of light absorbed versus the wavelength. o Cones have 3 different absorption pigments S, M and L regarding the wavelength of light they absorb best.

Electrical Signals in Neurons

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Resting Potential = the difference in potential of -70millivolts Action Potential = lasts a second, and is the signal which passes down the nerve which lasts (at each terminal) for approximately 1 millisecond. o It is a propagated response, meaning once it is triggered it travels all the way without decreasing in size. o Increasing the intensity of the stimulus will increase the frequency of the firing rate however it’ll never increase the intensity of AP (70mv to +40mv is set)  However there is an upper limit to the frequency, due to the refractory period - the interval between nerve impulses being created.

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o APs which occur without stimulus are spontaneous activity, establishing a baseline level of firing. o APs occur due to Na+ and K+ ions interacting in the axons. As the Na+ flows in K+ ions are forces out, returning the level of charge to -70mV. This is called the rising and falling phase of action potential. Synapses o The response can be either excitatory or inhibitory.  Excitatory occurs when ions become more positive due to depolarisation (they lose some –ve charge)  Inhibitory occurs through hyperpolarization, increasing negativity. o Why these responses exists is explained in chapter 3 (remember?) Centre-surround etc.

Neural Convergence and Perception  Signals are generated in the Receptors (R), travel to the bipolar cells (B) ad then to the ganglion cells (G) o Only the Ganglion cells have axons, which transmit into the optic nerve.  Two types of neurons connecting across the retina o Horizontal cells – which pass signals between receptors. o Amacrine cells – which pass signals between bipolar or ganglion cells.  Neural Convergence – is a result of 126:1 receptor to ganglion ratio. o Rods have a greater level of convergence of around 5:1 o While Cones run on a relative 1:1 ratio  Due to convergence rods-related ganglion cells fire more in darkness as they provide enough light units for excitation.  However being less convergent causes cones to have better visual acuity  This can be explained by why we always look directly at what we want to focus on, because then it is on our cone-rich fovea.  This also helps us to detect sources as the cone system is more accurate than the rod.

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Developmental Testing  Preferential Looking o A technique used to see if children prefer looking at one type of stimulus to another.  This works as we know children prefer to look at certain types of stimuli.  Visual evoked potential is a second method which uses electrodes to monitor electrical responses in the visual systems.  Acuity is very poor in a child around 20/400-20/600 o This is because the fovea is extremely underdeveloped at birth.

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Neural Processing and Perception Sensation & Perception Chapter 3 Notes

Neural Processing – The interaction of the signals in many neurons  Electrical signals will travel through the nervous system, interacting with neurons in order to find the correct direction – like a car taking a detoured route and relying on directions. o Rod = high convergence = high sensitivity o Cone = low convergence = high visual acuity Lateral Inhibition  The effect of both convergence and inhibition  Pivotal experiment done on a Limulus (Horseshoe Crab) by Hartline, Wagner and Ratliff (1956) o Limulus’ eye structure allows for stimulation of single receptors (A&B) o Stimulating A, then A and B, then increasing the intensity, showed a steady decrease in the response of receptor A. o This is due to the Lateral Plexus, cell for lateral transmission across the retina. What Lateral Inhibition explains  Hermann Grid o Remember: Perception is not determined by the receptor, but by the neurons farther down the system. o Taking 5 receptors with A at crossing; The bipolar cells receive the initial response (100) minus the inhibition of all the surrounding (0.1x100x4=40) therefore A receives 100-40=60 o Taking 5 receptors with D (central on line, not crossing) it receives the same treatment, yet as two receptors are on black they have a lower value (say 20) therefore the overall response of D is 100-(10+10+2+2)=76 o This supports lateral inhibition, as the lines end up brighter than the crossings, due to the inhibition by surrounding neurons.  Mach Bands – sharp borders. o In a shadow/change in brightness there is a slightly darker, then lighter band separating the two. (Test with shadow) o If the light is measured, this is not present, yet if it is observed it is. Therefore we can safely conclude that it is illusionary. o

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Simultaneous Contrast

o Explained by lateral inhibition, as the inhibition of square B (right) is less due to the darker background creating an inhibition of 2 vs 10. Therefore the right square appears brighter than the left square. o However the edges of the squares aren’t effected, therefore lateral inhibition can’t be the entire story. What Lateral Inhibition can’t explain  White’s Illusion o All the grey bars are the same colour. o However a lateral inhibition answer would predict B is darker, however it is clearly not. o Alan Gilchrist et al (1999) explained this through ‘belongingness’. As A should be white it appears darker and B should be black it appears lighter. o However this is not necessarily true, only a theory. Yet this phenomenon does suggest something else is clearly happening, not just lateral inhibition.

Processing from the Retina to the Visual Cortex  Receptive field – The region of the retina that must receive illumination in order to obtain a response in any given fibre.  This receptive field will overlap between many (hundreds-thousands) of receptors

Neural Processing and Perception  Centre-surround receptive field found in cats, not frogs. This can work in either excitatory-centre(A) inhibitory-surround(B) or visa versa. o Therefore if a stimuli is larger that A the inhibitory response of B will reduce the intensity of the firing rate. o However in the alternative (Excitatory surround) the firing will only occur with a large enough stimulus.

 From the eye  Occipital lobe (Striate cortex) as visual receiving area. – Signals from the retina and LGN (lateral geniculate nucleus)  LGN function: o 90% of optic nerve fibres lead to LGN o Information from LGN to cortex is less than Retina to LGN therefore one role must be to regulate which information passes. o Receives more information from the cortex than the retina, therefore this feedback may cause the mediation of data. Hubel and Wiesel’s study of Receptive Fields  Shining a light onto a screen, which the animal looked at.  Anesthetising the cat/monkey subject ensures the eye stays stationary. This allows for a spot on the screen to correspond directly with one on the eye  Remember: The receptive field is ALWAYS on the retina, even if the neuron is far from there.  Found the occipital lobe (Striate Cortex) has a side-by-side ‘centre surround’ configuration, called simple cortical cells.

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Therefore this (Simple Cortical Cell) would respond best to vertical bars of stationary light, for highest firing. The Orientation tuning curve shows which orientation a cell responds (fires most) to. We have neurons which respond to all orientations. This happened with moving stimuli (across the entire field of view), which fired best at a specific orientation. (These are Complex Cortical Cells) End-stopped Cortical cells respond not to movement but moving lines of specific length, or angle, or corners. This cemented the idea that neurons responded to select stimuli. All these cells are called Feature detectors

Do Feature detectors play a role in perception?  It is important to always measure the physiology-perception relationship between things.  Selective adaptation causes the cells to become fatigued, or to adapt. o 1) the neuron fires less o 2) the neuron fires less if the stimulus is again presented immediately  Contrast Threshold the minimum change to be perceived, can be individual. See p67 for test. o Ultimately, adapting to a vertical stimuli makes the threshold smaller.  This supports feature detectors as the increase in contrast threshold reflects that of the cortical tuning curve. Suggesting the psychological and the physiological share similar results, therefore are likely to be cause/effect. Selective Rearing  If an animal is reared in an environment which holds predominantly one orientation the number of neurons which respond to that stimuli will increase. Creating a ‘use it or lose it’ scenario o This may seem to contradict the previous role of feature detectors, however their effect is only on the immediate – not the long term.  Kittens reared for 5 months in a vertical environment appeared to ignore horizontal stimuli (a horizontal rod) but responded to vertical. (Blakemore and Cooper, 1970) o The cats reared in the vertical environment had no horizontal receptors and visa versa. Higher level neurons  Charles Gross removed he inferotemporal cortex (IT, in the temporal lobe) from monkeys and found it reduced their ability to recognise objects. With a similar thing found in humans, called prosopagnosia o This began to move away from the above ‘stick-figure’ physiology limitation.

Neural Processing and Perception

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o They found that neurons responded to real-life stimuli, such as hands or faces, which refused to fire in the presence of any other stimuli. Later experiments in the 80s and 90s solidified these findings, and resulted in the discovery in 1997 of the fusiform face area (underside of temporal lobe in human cortex) o Single neurons that respond to complex real-world stimuli are now considered the norm.

Specificity coding vs Distributed coding vs sparse coding.  Specificity, one neuron for one stimuli (Qu… Halle Berry experiment)  Distributed, large groups of neurons to complete a stimulus  Sparse Coding In between, fewer than distributed, but multiple fire for one stimulus.

Mind-Body problem  The Physiology does not always directly reflect the percept, as seen by the visual illusions.  NCC (Neural correlate of consciousness) is the relationship between the stimuli, neurons, and perception.  Easy problem of consciousness – is the NCC, where correlation between neural firing in certain zones has been found in relation to perception.  Hard problem of consciousness – the understanding of how the physical becomes the perceptual (potassium/sodium flowing)

Psychology 2018 Notes

Chapter 4 Perception Chapter 4 Notes

Spatial Organisation  V1 (primary visual cortex) - Specific locations on the Striate Cortex correspond to specific points on the retina – this is called the Retinotopic Map o This results in close activation on the retina corresponding to close neurons in the brain. o However mapping is not uniform, there is a larger surface area for corresponding fovial cells, which makes sense as there are more of them. Accounting for 8-10% of the retinotopic map. This inflation of small fovea to large cortex is called Cortical Magnification o Cortical Magnification acts to allow focusing on whatever is in the centre of the vision. o However as cortical magnification results in better detail – not larger size of the stimulus – it suggests that we don’t perceive exactly what our brain...