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PSYB51H3 (306)
Chapter 1

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Matthias Niemeier

PsyB51 Chapter 1 Sensation: The ability to detect a stimulus and, perhaps, to turn that detection into a private experience Perception: The act of giving meaning to a detected sensation Methods for Studying the Senses: 1. Thresholds (ex. what is the faintest you can hear?) 2. Scaling- measuring private experience (ex. do you taste food exactly the same as others do? Or see colour exactly the shade others do?) 3. Signal detection theory- measuring difficult decisions 4. Sensory neuroscience 5. Neuroimaging Quale: In philosophy, a private conscious experience of sensation or perception Gustav Fechner  Founder of experimental psychology  Believed in panpsychism  Described the relationship between mind and body using math  Coined psychophysics : The science of defining quantitative relationships between physical and psychological (subjective) events Earnst Weber  Interested in touch  Tested the accuracy of our sense of touch useing a special device. He measured the smallest distance between2 points that was required for a person to feel 2 points instead of one (two-point threshold)  Coined “Just Noticeable Difference” when experimenting with weights Dualism: The idea that the mind has an existence separate from the material world of the body Materialism: The idea that the only thing that exists is matter, and that all things, including the mind and consciousness, are the results of interactions between bits of matter Panpsychism: The idea that the mind exists as a property of all matter- that is that all matter has consciousness Two-point threshold: The minimum distance at which two stimuli are just perceptible as separate Just Noticeable Difference (JND) or difference threshold: 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 Weber Fraction: The constant of proportionality in Weber’s Law Weber’s Law: The principal describing the relationship between stimuli and resulting sensation that says the JND is a constant fraction of the comparison stimulus Fechner’s Law: A principal describing the relationship between stimulus and resulting sensation that says the magnitude of subjective sensation increases proportionally to the logarithm of the stimulus intensity (Fechner’s law extends upon Weber’s Law) - S=K log R - Where S is the psychological sensation, which is equal to the logarithm of the physical stimulus level (log R) multiplied by a constant, K. - This equation describes the fact that our psychological experience of the intensity of light, sound, smell, taste, and touch increases less quickly than the actual physical stimulus increases Absolute Threshold: The minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time Psychophysical Methods Method of Constant Stimuli: A psychophysical method to measure an absolute threshold in which many stimuli, ranging from rarely to almost always perceivable (or rarely to almost always perceivably different from a reference stimulus), are presented one at a time. Participants respond to each presentation: “yes/no”, “Same/different”, and so on - its best to repeat the stimulus at different levels over and over again to make sure the person can/can’t hear it in case of a distraction or other reason - in general the intensity at which a stimulus would be detected 50% of the time is chosen as threshold Method of Limits: A psychophysical method in which the particular dimension of a stimulus, or the difference between 2 stimuli, is varied incrementally until the participant responds differently - instead of a random presentation of stimuli, the stimulus is presented in order of increasing or decreasing intensity - when the stimulus is presented from the least intense to the most intense, participants must report when they notice that stimulus (hear it for example) and vice versa - there is some overshoot with this method; it usually takes more intensity to report hearing the tone when the intensity is increasing, and it takes more decreases in intensity before a listener reports the tone cannot be herd Method of Adjustment: A method of limits in which the subject controls the change in the stimulus Scaling Methods and Supertasters Magnitude Estimation: A psychophysical method in which the participant assigns values according to perceived magnitudes of the stimuli - ex. rate the sweetness of this candy between 1 and 10 - sometimes the experimenter will pick a stimulus to be a 10 or a 1 for example so the participant has something to compare the rest of the stimuli to 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 b - S= aI - States that the sensation (S) is related to the stimulus intensity (I) by an exponent (b) - Pg 10 explains this with examples A comparison of the 3 laws presented: Weber’s Law: - Involves clear objective measurement. We know how much we varied the stimulus , and either the observers can tell that the stimulus has changed or cannot Fechner’s Law: - Begins with the same sort of objective measurement as Weber’s, but the law is actually a calculation based on some assumptions about how sensation works. - Fechner’s law assumes that all JNDs are perceptually equivalent (which is not correct in all cases we know now) Steven’s Power Law: - Describes rating data quite well, but notice that the rating data are qualitatively different from the data that supported Weber’s law. - We can record the subjects ratings and check if they are reasonable, but there is no way to know whether they are objectively right or wrong Cross Modality Matching: The ability to match the intensities of sensations that come from different sensory modalities. This ability enables insight into sensory differences. - For example, a listener might adjust the brightness of a light until it matches the intensity of a tone. Supertasters: An individual whose perception of taste sensations is the most intense 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 from a series of presentations are sensitivity (d’) and criterion of the observer - In short when people are detecting the smallest sound they can hear for example, they have to do it with their own internal “noise” (since no situation will ever be absolutely quiet, absolutely dark etc.) Criterion: In signal detection t
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