Complete Psychology of Perception Notes (I 4.0ed this cours..
Complete Psychology of Perception Notes (I 4.0ed this course)

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Boston University
Psychological & Brain Sciences
CAS PS 222

PSYCHOLOGY OF PERCEPTION • Saccades – the time when you move from fixation to fixation o 2-3 saccades per second o During this saccade we don't see much • Blindsight – seeing without knowing it o Medical condition where people are blind but can actually see, they can avoid obstacles • Motion induced blindness – the pink circle disappears when you fixate in the middle o Always need changing/moving things for us to perceive • EVOLUTION o Perception and your sense of reality are the products of evolution o Sensory systems provide a survival advantage o Importance of type of energy in the environment for an animal determine which senses have developed o Human senses are limited to only certain kinds of energy in the environment o Therefore, humans’ sense of reality is also limited • Limit of our perception, some species sense energies that humans cannot o Bees see ultraviolet light o Rattlesnakes sense infrared energy o Birds, turtles, amphibians use magnetic fields to navigate o Duck-billed platypus can sense electric fields • Nativism – the idea that some skills are not derived from external sources, and that we have abilities and knowledge that are innate and not learned • Empiricism – the idea that all knowledge comes through the senses. Perception is the source of all knowledge about the world • Dualism – the idea that both mind and body exist and are separate entities • Monism – the idea that mind and matter are formed from, or reducible to, a single ultimate substance or principle of being o god • Materialism – the idea that physical matter is the only reality and everything, including the mind, can be explained in terms of matter and physical phenomena • Mentalism – another form of monism. The idea that the mind is the true reality and objects exist as aspects of the mind’s awareness PHILOSOPHERS AND PHYSICISTS • Gustav Fechner – invented psychophysics o first who really tried to measure perception o Psychophysics – the science of defining quantitative relationships between physical and psychological (subjective) events o Also believed in panpsychism – the idea that all matter has consciousness. Every matter has a soul o Fechner/bentham color illusion – perceiving color where there is none o Fechner’s law – a principle describing the relationship between stimulus magnitude and resulting sensation magnitude  Intensity of a sensation may increase in arithmetical progression, the stimulus must increase in geometrical progression  Geometrical is the one that is x2 • Ernest weber o Just noticeable difference changes in proportion o Intensity and noticeable difference (DI) is linearly proportional o Just noticeable difference – is a logarithmic function  The brighter the more intense…yeah woops candles in the dark o Absolute threshold – the minimum intensity of a stimulus that can be detected with a given degree of confidence (50% maybe) • Two point touch threshold – the minimum distance at which two tactile stimuli can be distinguished ESTIMATING THRESHOLDS • 3 main methods • Method of constant stimuli – many stimuli ranging from rarely to almost, and present all of them many many times. then you see what percentage of time • Method of limits – the magnitude of a single stimulus or the difference between two stimuli is varied incrementally until the participants responds differently o Go from loud to not very loud and see when the participant cannot hear. Then take the average of many trials o Trials stop when participant says no o Go from high to low and low to high • Method of adjustments – similar to the method of limits, but the participant controls the stimulus directly o A lot faster but the method isn’t very good • How to measure sensation o Magnitude estimation: the participant assigns values according to perceived magnitudes of the stimuli  Rate your pain on a scale of 1-5  Stevens’ power law: a principle describing the relationship stimulus magnitude and resulting sensation magnitude, such that the magnitude of subjective sensation is proportional to the stimulus magnitude raised to an exponent. S=kl^a SUMMARY • Weber’s law: linear relationship DI=kl. An objective measurement of the minimum stimulus change that can be perceived • Fechner’s law: logarithmic relationship DS= k log l. An estimate of our sensation based on the assumption that all JNDs are perceptualy equivalent. It is not always true • Steven’s law: power relationship DS=kl^a. a description model of rating data. It fits data well, but there is no way to know whether it is a correct estimation of sensation because it is subjective. MEASURING PERCEPTION • Cross modality matching – the participant matches the intensity of a sensation in one sensory modality with the intensity of a sensation in another o Example: match the bitterness of PROP to the experience of the sound of a fire engine. • A more modern approach: signal detection theory – a psychophysical theory that quantifies the response of an observer to the presentation of a signal in the presence of noise o So there is a signal, which is the true cancer. And there is “noise” which is everything else besides the cancer. It’s like the distraction o Four possible stimulus/response situations in signal detection theory Stimulus present Stimulus absent Answer yes Hit False alarm Answer no Missed Correct rejection • Correct rejection on responding to left of criterion under red curve • Hit on responding to right of criteria under blue curve • False alarm on responding to right of criterion under red curve • Missed on responding to left of criterion under blue curve • Red is shower noise alone • Blue is shower noise+phone • Sensitivity - D’ is the distance between the peak of two distributions. The larger d’ is the better o If D’ is larger, then there is higher sensitivity, meaning its easier to detect the difference of a fly and a plane • Receiver operating characteristics (ROC) – graph of hit over false alarm BIOLOGY OF PERCEPTION • Johannes muller – stating that the nature of a sensation depends on which sensory fibers are stimulated, not how the fibers are stimulated • Some areas of the brain are polysensory, info has combined senses • Hermann von helmoltz – first person to measure the speed of neural impulses o First to realize how the cochlea works o invention of the ophthalmoscope • Red eyes - The red color comes from light that reflects off of the retinas in our eyes. In many animals, including dogs, cats and deer, the retina has a special reflective layer called the tapetum lucidum that acts almost like a mirror at the backs of their eyes. If you shine a flashlight or headlights into their eyes at night, their eyes shine back with bright, white light. Humans don't have this tapetum lucidum layer in their retinas. If you shine a flashlight in a person's eyes at night, you don't see any sort of reflection. The flash on a camera is bright enough, however, to cause a reflection off of the retina -- what you see is the red color from the blood vessels nourishing the eye. • Santiago ramon y cajal o Created incredibly detailed drawings of neurons and neural structure • Charles Sherrington – discovered the synapse • Otto loewi – He dissected out of frogs two beating hearts: one with the vagus nerve which controls heart rate attached, the other heart on its own. Both hearts were bathed in a saline solution (i.e. Ringer's solution). By electrically stimulating the vagus nerve, Loewi made the first heart beat slower. Then, Loewi took some of the liquid bathing the first heart and applied it to the second heart. The application of the liquid made the second heart also beat slower, proving that some soluble chemical released by the vagus nerve was controlling the heart rate. He called the unknown chemical Vagusstoff. It was later found that this chemical corresponded to Acetylcholine FREQUENCYANALYSIS (Fourier spectral) • Spatial frequency: the number of cycles of a grating per unit of visual angle (usually specified in degrees) • All images can be remade with TONS of gratings with different frequencies, amplitudes, and phase (position) with a sin wave. o Metaphor: making a cake. You have all the ingredients to make the cake. The ingredients for a picture are the gratings. o The gratings are the exact same size o Amplitude is contrast in vision o Frequency is sharpness in vision o Phase is relative position of grating in vision NEURONS • So calcium comes in at the end which causes the synaptic vesicles to release the neurotransmitters (calcium pushes vesicles towards the membrane) • EEG (ELECTRIC) o takes measures from specific neurons in your brain o You take many measurements and then you average them to get an averaged ERP waveform. • MEG (MAGNETIC) o A technique similar to EEG that measures changes in magnetic activity across populations of many neurons in the brain o Not a lot of spacial recognition, but you can see how things change over time • CAT o An imaging technology that uses x rays to create images of slices through volumes of material o Beams of x rays in different direction • MRI o Uses the responses of atoms to strong magnetic fields to form images of structures like the brain o Structural image • fMRI o measures localized patterns of activity in the brain o activated neurons provoke increased blood flow, which can be quantified by measuring changes of oxygenated and deoxygenated blood to strong magnetic fields o blood oxygen level dependent signal: the ratio of oxygenated to deoxygenated hemoglobin that permits the localization of brain neurons that are most involved in task • PET o An imaging technology that allows us to define locations in the brain where neuron
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