PSYC 220 The Senses Test 1 Philosophical Foundations o 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 am o How do you define real o Radical Skepticism We can believe nothing about our world o Dualism The body and soul are separate o Materialism our perceptual world i e consciousness is an emergent property of our own Our perception is not the same as the physical world o Na ve Realism We see world a certain way because that is the way the world really is DO body s activity NOT BE We can t perceive what we can t see Our perceptions are seldom in line with the exact physical situation Some animals are able to sense stimuli that humans cannot Just because we can senses something doesn t mean we can perceive it Division into physics bio and perception o Environment physics Organism Bio Perception Psychology Physiology physiological psychology psychophysics History o 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 causality o Locke and the empiricists vs Kan and rationalists o 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 experimental psychology Fechner 1801 1887 invented psychophysics thought to be the true founder of Relating changes in the physical world to changes in our psychological experiences Perception doesn t just happen o 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 tree Class 2 Brain o Brains from different mammals have similar structures o 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 complexity o All brains contain neurons Communication within a neuron Neural Signals o Neurons are surrounded by a solution containing ions carry electrical charge 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 Potentials o 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 sec o Show spontaneous activity that occur without stimulation o If stimulus is strong enough causes increase in action potential firing rate above baseline threshold Synaptic Transmission of Neural Impulses across a neuron o NTs are released by the presynaptic neuron from vescicles o Received by the postsynaptic neuron on receptor sites o Used as a trigger for voltage change in the postsynaptic neuron o 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 techniques o Computerized Axial Tomography CT o Magnetic Resonance Imaging MRI Measures magnetic field generated as hydrogen atoms spin back to aligned state atoms No magnetic field random alignment Magnetic Field homogeneous magnetic field alignment of H Radio Wave Controlled tilt of H atoms o Diffusion Tensor Imaging DTI o Angiogram stroke aneuryism carotid artery o fMRI show degenerative disorders of the brain alzheimer s Cortical atrophy Psychophysics Heavier vs Weighs more perception is different Fechner invented psychophysics experimental psychology o Changes in our physical world relate to changes in our psych experiences o Oct 22 1850 Detection o Absolute threshold smallest amount of energy needed to detect a stimulus o 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 Reversals o 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 threshold o Weber fraction Taste saltiness 083 Vision brightness 079 Audition loud 048 Touch heaviness 020 SO more sensitive to touch than to saltiness o Fechner s Law S k ln I o SS Stevens Power law S cI n Magnitude estimation If less than 1 decelerating more than 1 accelerating Three way lightbulb the more you change the intensity the less response you get o As the stimulus becomes stronger the signal becomes stronger than the noise o 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 response criteria into account o Noise distribution Signal noise distribution where target is Beta decision criteria line d prime estimate of your sensitivity ROC curve plots of hits vs false alarms Eyes First evidence Cambrian era 530 mill years ago Light electromagnetic radiation Quality image needs a lot of light Field of view Our eyes move o