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Sensation and Perception CH. 1 INTRODUCTION Sensation: the ability to detect a stimulus and, perhaps, to turn that detection into a private experience • The ability to detect the pressure of a finger Perception: the act of giving meaning to a detected sensation How you understand the finger that runs down your back Thresholds: the range of senses you can handle Psychophysics: defines the quantitative relationships between physical and psychological (subjective) events. The relationship between sensation and the energy that gave rise to that sensation • Gustav Fechner (1801-1887)—mind and body relations o Fechner’s Law—a principle describing the relationship between stimulus and resulting sensation that says the magnitude of subjective sensation increases proportionality to the logarithm of the stimulus intensity  An extension of weber’s law o Absolute threshold—the minimum amount of stimulation necessary to detect a stimulus 50% of the time o Measuring: the higher the stimulus intensity, the higher the firing rate of neurons (the more the intensity of the stimulus, the more likely the “yes” response to it is) • Ernst Weber (1795-1878)—touch o Two-point touch threshold—used a compass like tool to measure the smallest distance between two points that was required for a person to fell two points instead of one o Just Noticeable Difference (JND)—the smallest detectable difference between two stimuli, or the minimum change in a stimulus that enables it to be correctly judged as different from a reference stimulus.  The difference required for detecting a change in weights o Weber’s Law—JNDs change systematically in a specific ratio  Size of difference is a constant proportion of the stimulus intensity  The principle describing the relationship between stimulus and resulting sensation that says the just noticeable difference (JND) is a constant fraction of the comparison stimulus  Involves a clear objective measurement. We know how much we varied the stimulus, and either the observers can tell that the stimulus changed or they cannot Psychophysical Methods: • Method of constant stimuli—Many stimuli, ranging from rarely to almost always perceivable are presented one at a time. Participants respond to each presentation: “yes/no” “same/different” o Creating many stimuli with different intensities in order to find the tiniest intensity that can be detected • Methods of limits—the particular dimension of a stimulus, or the difference between two stimuli, is varied incrementally until the participant responds differently o The point at which you can detect a stimuli (controlled by experimenter) o Instead of random presentation, tones are presented in order of increasing or decreasing intensity • Method of adjustment—the point at which you can/cannot detect a stimuli until you determine the avg. point at which you can just detect it and the point at which you cannot detect it. o The subject in this case is the one who steadily increases of decreases intensity of the stimulus • Magnitude estimation: the participant assigns values according to perceived magnitudes of the stimuli o Works best when the observers are free to choose their own range of numbers • Steven’s Power Law—a principle describing the relationship between stimulus and resulting sensation that says the magnitude of subjective sensation is proportional to the stimulus magnitude raised to an exponent o Going from 1 to 10 lit candles can be dramatic. But adding 10 candles to 100 is less dramatic and adding 10 to 10,000 is even less dramatic Cross-Modality Matching: the ability to match the intensities of sensations that come from different sensory modalities. This ability enables insight into sensory differences. • An observer adjusts a stimulus of one sort to match the perceived magnitude of a stimulus of a completely different sort. • Ask a listener to adjust the brightness of a light until it matches the loudness of a particular tone Signal Detection Theory: a psychophysical theory that quantifies the response of an observer to the presentation of a signal in the presence of noise. Measures obtained form a series of presentations are sensitivity and criterion of the observer • No matter how quiet the room and area you are in, you will ALWAYS be able to hear something or no matter how dark a room, you will always be able to see something • Criterion: an internal threshold that is set by the observer. If the internal response is above criterion, the observer gives one response. Below criterion gives another response o Adjusting your criterion may change your results o You are in the shower, that is noise, and you hear what may be a phone ringing, this is the signal. You must now determine whether to run naked and dripping to find the phone (nervous system exceeds criterion) or decide there isn’t a phone ringing and remain in the shower (below criterion). o *Hit: stimulus is there and you detect it o Miss: stimulus is there and you don’t detect it o False alarm: stimulus is not there, but you detect it o *Correct rejection: stimulus is not there and you don’t detect it o Adjusting the criterion level: the intensity of the stimulus also change the results o Increase changes sensitivity and where your criterion is • ROC Curve: the graphical plot of the hit rate as a function of the false-alarm rate. If these are the same, points fall on the diagonal, indicating that the observer cannot tell the difference between the presence and absence of the signal. As the observer’s sensitivity increases, the curve bows upward toward the upper left corner. That point represents a perfect ability t distinguish signal from noise (100% hits, 0% false alarms). Sensory neuroscience Johannes Muller: Wrote the Handbook of Physiology. Wanted to understand how we sense the world. Do we actually understand the outside world and what is going on inside our bodies and minds • Doctrine of Specific Nerve Energies: the nature of a sensation depends on which sensory fibers are stimulated, not on how fibers are stimulated. o It doesn’t matter what is stimulating the neurons, it is that they are being stimulated that will give you the stimulation o We are aware only of the activity in our nerves, and we cannot be directly aware of the world itself o Important to know which nerves are stimulated, not how Cranial Nerves: twelve pairs of nerves (one for each side of the body) that originate in the brain stem and reach sense organs and muscles through openings in the skull • They follow a specific order • Dedicated mainly to sensory and motor systems Herman von Helmholtz • Thought that the brain and behavior obeyed physical laws. All behaviors should be explained by physics only. • Measured the speed of nerve conduction—how fast our signals send from one part of the body to the other o Frog—90 ft/s o Human—165-330 ft/s Neuronal connections • Cajal—depicted neurons as separate cells with tiny gaps between them o He found that neurons do not touch each other. They bump up next to each other, but they do not come in contact to deliver messages • Sherrington—how the connections between neurons work o Named the synapse—the tiny gap between the axon of one neuron and the dendrite of the next o Speed of neural transmission decreases at the synapse • Loewi—believed that the transmission at the synapse was chemical not electrical o Experiment—took a frogs heart, it will still beat if put in saline  One heart had the vagus nerve attached and the other had it removed  If vagus was still attached, it still beat st nd  Stimulate vagus nerve of 1 heart, which slowed the heart, and poured saline mixture on 2 heart which slowed the heart • Alan Hodgkin &Andrew Hukley: o Squid neuron experiment—discovered tat neural firing is actually electrochemical o Isolated neurons form the quid and tested how the nerve impulse travels along the axon.  Because the axons were so large, they were able to pierce the axon with an electrode to measure voltage, and inject chemicals inside Neural Firing • EEG: a technique that, using many electrodes on the scalp, measures electrical activity form populations of many neurons in the brain o Doesn’t pinpoint exactly where they are, but gives a rough idea as to where they are o Measures how quickly responses are happening—time related issues • ERP: a measure of electrical activity form a subpopulation of neurons in response to particular stimuli that requires averaging many EEG recordings. o The brains response to a prick of the skin or a flash of light • MEG: measures changes in magnetic activity across the populations of many neurons in the brain o Takes advantage of the fact that neurons make very small changes in their local magnetic fields in addition to small electrical changes Neuroimaging: traditional X-rays. Only show structure, not detail • CT: uses x-rays to create images of slices through volumes of material • MRI: uses the responses of atoms to strong magnetic fields to form images of structures like the brain. The method can be adapted to measure activity in the brain, as well • fMRI: a variant of magnetic imaging that makes it possible to measure localized patterns of activity in the brain. Activated neurons provoke increased blood flow, which can be quantified by measuring changes in the response of oxygenated and deoxygenated blood to strong magnetic fields • PET: enables us to define locations in the brain where neurons are especially active by measuring the metabolism of brain cells using safe radioactive isotopes. CH. 2 FIRST STEPS IN VISION Light—physical stimulus of electromagnetic radiation • Wave: an oscillation that travels through a medium by transferring energy from one particle or point to another without causing any permanent displacement of the medium • Particle (photon): a quantum of visible light or other form of electromagnetic radiation demonstrating both particle and wave properties • Absorbed: to take light, noise, or energy and not transmit it at all • Scattered: to disperse light in an irregular fashion • Reflected: to redirect something that strikes a surface—especially light, sound, or heat—usually back toward its point of origin • Transmitted: to convey something from one place or thing to another • Refracted: to alter the course of a wave of energy that passes into something from another medium, as water does to light entering it from the air Environment  Optic array—what the person sees Range of vision  60° up  80° down  110° visible with both eyes  190° with visibility in only one eye Parts of the Eye • Aqueous humor: the watery fluid in the anterior chamber of the eye o Supplies oxygen and nutrients to, and removes waster from, the cornea • Crystalline Lens: the lens inside the eye that enables the changing of the focus o Clear, so no blood supply o Controlled by ciliary muscles o Accommodation: the process by which the eye changes its focus  Decreases with
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