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Chapter 1

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University of Toronto Scarborough
Matthias Niemeier

PSYB51 Chapter 1 -ability to detect pressure of a finger and than maybe turn that detection into a private experience is sensation. -Perception is the act of giving meaning to thse sensations (how do you understand the finger running down your back) -variety of methods used in the study of senses >Thresholds, Scaling (measuring private experience), Signal Detection Theory, Sensory Neuroscience, and Neuroimaging -Thresholds: Fechner, relationship between mind and matter (dualism and materialism). Dualists say the mind has existence separate from material world of body and Materialists say the mind is NOT separate (mind is what the brain does) >Fechner proposed that the mind/consciousness is present in all of nature. Panpsychism: mind exists as a property of all matter. >Fechners goal was to show relation b/w mind (sensation) and matter (energy) using math. Called his methods and theory psychophysics >he was inspired by Weber who was interested in touch, tested the accuracy of our sense of touch. Used something like a compass (from geometry set) to measure the smallest distance b/w two points that was required for a person to feel two points instead of one. Fechner called this distance two-point touch threshold. >Weber would ask people to live a standard weight (weight stayed same over all the trials) and a comparison weight that differed in incremental amounts. Found that the ability of someone to detect a difference b/w the standard and comparison weight depended on the weight of the standard. When the standard was relatively light peple were BETTER at detecting a small diff when lifting the comparison weight. When the standard was heavier people needed a bigger difference before they could detect a change. He called this difference Just Noticeable Difference (JND). Another name forJND (smallest change in a stimulus tht can be detected is difference threshold) >Weber noticed that JNDS change in a systematic way. Smallest change in weight that was detected was always close to 1/40 of the standard weight. (i.e a 1g change could be detected when the standard weighed 40g. a 10g change was required with standard was 400g). he studid JNDs for other stimuli (brightness, pitch, time etc) and found that a constant ratio b/w change and what was being changed could dexcribe the threshold of detection. Frechner called these Weber Fractions >the size of the detectable diff (delta I) is a constant proportion (K) of the level of the stimulus (I) Weber’s Law >Frechner found a way to describe the relationship b/w mind and matter. Assumed the smallest detectable change in a stimulus (delta I) could be considered a unit of the mind (the smallest bit of change that’s perceived). Extended Weber’s law to make Frechner’s Law (describe relationship b/w stimulus and resulting seneation that says the magnitude of subjective sensation inc proportionally to the logarithm of stimulus intensity >our psychological experience of the intensity of light, sound, smell, taste, touch inc LESS QUICKLY than the actual physical stimulus increases. >Absolute Threshold: minimum amount of stimulation necessary for a erson to detect a stimulus at least 50% of the time. -Psychophysical Methods: method of constant stimuli (creating many stimuli with diff intensities to find the tiniest intensity that can be detected. >in this test the intensities of the stimuli would be not too far above or below the intensity where your threshold was expected to be. The tones would vary in intensity and be presented randomly, multiple times. Need to repeat the measure over and over again and then average out the responses. (observer varies, his attention might be somewhere else). >method of limits: experimenter begins with the same set of stimuli (e.x tones that vary in intensity). The tones are presented in dec or inc order. When presented in increasing order, listeners are asked to say when they first hear the tone. And hen going in dec order the listener says when the tone is no longer audible. >usually takes more intensity to report hearing the tone when intensity is inc, and it takes more dec in intensity before listere says the tone can no longer be heard. Take average of the crossover points (when listener shiter from reporting hearing the tone to not hearing it) as the threshold. >another measure of thresholds is method of adjustment. The subject is the one who inc or dec the intensity of the stimulus. Not usually used to measure thresholds bc its hard to get people to reliably adjust intensity to the same value across people/time -Scaling Methods: seeing the magnitude of your experiences. Magnitude of estimation: give observers a series of sugar solutions and ask them to assign numbers to the samples, the numbers only have to make sense to the observer. Sweeter solutions should get bigger numbers, and if solution A seems twice as sweet as B, it should get twice the number assigned to B. >participant assigns values according to perceived magnitudes of the stimuli >Stevens Power Law: describes the relationship b/w stimulus and the resulting sensation. says the magnitude of subjective sensation is proportional to the stimulus magnitude raised to an exponent. >e.x you have some lit candles, then you light 10 more. If you started with 1 candle, the change from 1-11 is pretty dramatic. But if you add 10 to 100 lit candles, the change will be modest. Adding 10 to 10,000 wouldn’t even be noticeable. Another e.x is adding an inch to a spider changes my sensory experience way more then adding an inch to an elephant. >cross-modality matching: ability to match the intensities of sensations that come from diff sensory modalities. E.x is asking person to adjust the brightness of a light until it matches the loudness of a t
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