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Chapter 5

chapter 5

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University of Toronto St. George
Michael Inzlicht

Psychology 100 Chapter 5 Notes Sensation, Perception and Attention Story about Helen Keller explaining that perception is the only bridge we have to the world. How Do We Sense Our Worlds? Sensory organs gain information by converting forms of physical energy into signals that our brain can understand. This system has been evolved, to solve adaptive problems. Each animal is sensitive to different types of physical energy, because each faced different adaptive problems. o Ex. Animals that hunt at night, have poor vision by excellent hearing Stimuli Must Be Coded to Be Understood by the Brain Sensory coding the way our sensory organs translate stimulis physical properties into neural impulses different features of the environment are coded by different patterns of neural activity. Receptors are specialized neurons in the sense organs that pass impulses to connection neurons when they receive physical or chemical stimulation. This is called transduction. o After transduction in the receptors, connection neurons in the sense organs transmit information to the brain, in form of neural impulse. Most sensory information first goes to the thalamus (structure in middle of brain) o Neurons in the thalamus then send info to the cortex where incoming neural impulses are interpreted as the five senses. Sensations refer to the transduced message that is carried by nerve impulses. Sensory coding two categories o Quantitative - intensity, brightness, and loudness (often indexed by the neural firing frequency higher the firing frequency the brighter, louder etc. the stimulus. more intense stimuli need to recruit more neurons. o Qualitative color and taste possible because different sensory receptors respond to different qualities of stimulus. Involves coarse coding > sensory qualities are coded by only a few receptors, each of which respond to a broad of range of stimuli. Psychophysics Relates Stimulus to Response 1 www.notesolution.com Psychophysics - the study of physical properties and how we sense or perceive them. Sensory Thresholds Absolute Threshold - How much of a physical energy source needs to be presented before our sensory organs detect it. The minimum intensity. o Ex. Faintest sound a person can hear. Difference Threshold just notable difference between two stimuli. The difference threshold increases at something is very noticeable. Principle of Webers law the size of a just noticeable difference is based on a relative proportion of difference rather than a fixed amount of difference. o Ex. Getting 610 on a test, or 96100 (both four points separate, but mean different things) the percentage is the important thing, not that absolute size of difference. Signal-Detection Theory An absolute threshold is not concrete, because of variable human judgment. Signal-detection theory detecting a stimulus requires making a judgment about its presence or absence, bias on a subjective interpretation of ambiguous information. o Ex. Task of radiologist has to make judgment calls, on whether someone has cancer. > Draws from previous health, age and family history etc. factors also motivation and attention of radiologist. Signal-detection is based on a series of trials some stimulus is presented, some it isnt. o One of four outcomes hit (correct) miss (failure to detect true signal) false alarm (detects a stimulus that wasnt even there) correct rejection (chooses correctly that the stimulus wasnt there) o The observers sensitivity is computed by comparing the hit rate, with the false-alarm rate. Response bias refers to the participants tendency to report the stimulus on ambiguous trials. Sensory Adaptation Your response to a stimuli changes over time. Sensory adaptation o Ex. When construction starts, when youre in a quiet place, you can notice it, overtime it starts to fade into the background. When certain aspects in our environment change, it is important for us to realize it, however it is less important for us to keep responding to 2 www.notesolution.com
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