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PSYC 220: The Senses Test 1- Philosophical Foundationso Rene Descartes (1596-1650) Everything you know comes from your senses Senses sometimes deceive him (illusions) Dreams appear real An “evil genius” could be manipulating his senses Cogito Ergo Sum- I think therefore I amo How do you define real?o Radical Skepticism We can believe nothing about our worldo Dualism- The body and soul are separateo Materialism- our perceptual world, i.e.- consciousness is an emergent property of our own body’s activity- Our perception is not the same as the physical worldo Naïve Realism- We see world a certain way because that is the way the world really is – DO NOT BE We can’t perceive what we can’t see.  Some animals are able to sense stimuli that humans cannot Just because we can senses something doesn’t mean we can perceive it Our perceptions are seldom in line with the exact physical situation- Division into physics, bio, and perceptiono Environment (physics)  Organism (Bio)  Perception (Psychology) Physiology, physiological psychology, psychophysics- Historyo Why do we study perception? Practical- When observations turn out to be error it may lead to acidents- We may want to replace the real world with some specially prepared substitute- We may wish to use a machine to replace or supplement a human observer- Medical diagnosis or treatment- Perceptual questions concerning consumer preference Philosophical Curiosity- What do we see? Space, time, causalityo Locke and the empiricists vs. Kan and rationalistso Common sense- Descartes- How behavior determines many of our actions Understanding how the brain works- 10 bill to 1 trill neurons in the brain-o Dawn of Psychophysics Fechner (1801-1887) invented psychophysics, thought to be the true founder of experimental psychology- Relating changes in the physical world to changes in our psychological experiences- Perception doesn’t just happeno Sun sends out energy in many different directions/ some fraction of that energy hits a tree  reflected light is scattered in different directions/some fraction reaches the observer and forms an image in the back of the eye  the light signal is TRANSDUCED into neural signals by receptor cells in the back of they eye  neural signals are transmitted from one neuron to the next until it reaches cells in the visual receiving area of the brain  the signals continue to be processed and analyzed by neurons in the visual receiving area and later of the brain  perception of the treeClass 2- Braino Brains from different mammals have similar structureso Nervous System The structure of the nervous system- tells us about brain function Brain organization- Mammilian plan Similarities- divided in 2, fissures, cerebellum, sits on top of spine- Development-  Differences- complexityo All brains contain neurons  Communication within a neuron- Neural Signalso Neurons are surrounded by a solution containing ions (carry electricalcharge) Na+/K+(positive) and Cl- (negative) electrical signals are generated when ions cross the membranes of the neurons- When voltage occurs, channel opens, NA rush in/K rushes out  depolarizd  channel closes  na leaves through another channel  hyperpolarized = balanced Membranes have selective permeability Electricity is transmitted in neurons by changes in membrane potential (determined by voltage gated ion channels)- Properties of Action Potentialso Show propagated response, remain the same size regardless of stimulus intensity, increase in rate to increase in stimulus intensity (rate)o Have a refractory period of 1 ms, firing rate is 500-800 impulses/seco Show spontaneous activity that occur without stimulationo If stimulus is strong enough, causes increase in action potential, firing rate above baseline (threshold)- Synaptic Transmission of Neural Impulses across a neurono NTs are released by the presynaptic neuron from vescicleso Received by the postsynaptic neuron on receptor siteso Used as a trigger for voltage change in the postsynaptic neurono Types of NTs Excitatory Transmitters- cause depolarization- Neurons become more positive, increases likelihood of an action potential Inhibitory NT- cause hyperpolarization- Neuron becomes more negative, decreases likelihood of action potential Organization of the cortex- occipital- vision, temporal- sound- Imaging techniqueso Computerized Axial Tomography (CT)o Magnetic Resonance Imaging (MRI) Measures magnetic field generated as hydrogen atoms spin back to aligned state- No magnetic field- random alignment - Magnetic Field- homogeneous magnetic field, alignment of H atoms- Radio Wave- Controlled tilt of H atomso Diffusion Tensor Imaging (DTI)o Angiogram- stroke, aneuryism, carotid arteryo fMRI show degenerative disorders of the brain (alzheimer’s)- Cortical atrophyPsychophysics- Heavier vs. Weighs more- perception is different- Fechner invented psychophysics/experimental psychologyo Changes in our physical world relate to changes in our psych experienceso Oct 22, 1850- Detectiono Absolute threshold- smallest amount of energy needed to detect a stimuluso Difference threshold- smallest detectable difference between stimuli (compares more than one stimulus)o Psychometric function- at 50%, is the threshold Psychophysical function measures 2 psychometric functions o Method of Constant Stimului  Alcohol in orange juice, threshold Staircase method- GREs graded, Reversalso Weber’s Law- when does something go above the threshold DL= (K) (Base stimulus) or DL/S= K- K= coefficient o Determine JND by Method of Constant Stimuli  At 50% thresholdo Weber fraction  Taste- saltiness- .083 Vision- brightness- .079 Audition- loud- .048 Touch- heaviness- .020 SO, more sensitive to touch than to saltinesso Fechner’s Law- S= k ln (I) Three way lightbulb- the more you change the intensity, the less response you geto SS Stevens Magnitude estimation Power law S= cI^n- If less than 1, decelerating/ more than 1, acceleratingo As the stimulus becomes stronger, the signal becomes stronger than the noiseo Absolute threshold There are differences in response criteria among participants- bias- Lax responder vs. strict responder - People of have different reponses, but sensitivity elvel for both of them may be the same Overcoming internal bias- Signal detection theory takes individual’s


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AU PSYC 220 - Test 1

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