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Lecture 9

Unit 2 - Lecture 9 - Psychophysics.docx

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Department
Psychology
Course
PSYO 1011
Professor
n/a
Semester
Fall

Description
PSYO 1011 Psychophysics 1 Lecture 9: Psychophysics October 13, 2009 Sensation & Perception: • Sensation o Involves transduction of the physical world into neural impulses o Stimulus­detection process by which sense organs respond to & translate environmental  stimuli into nerve impulses that are sent to the brain • Perception o Involves binding these sensory impulses into a representation of the world o Makes ‘sense’ of what our senses tell us  Active process of organizing stimulus input & giving it meaning • REF: Figure 5.1 (170) Sensory Processes: • Sensory impulses processed by distinct brain regions • 5 classical senses o Vision, hearing (audition), touch, taste (gustation) & smell (olfaction) o Can be subdivided into separate senses • Note: There are other senses o i.e.) Senses that provide info about balance & body position • Psychophysics o The relationship between physical stimuli & the sensations about them that we  experience o Psychophysicists study  Detection  Discrimination  Scaling o Concerned w/ 2 types of sensitivity  Absolute limits of sensitivity  Sensitivity to differences between stimuli Measuring Sensory Thresholds: • Detection (Sensory) Threshold o The quantitative amount of a stimulus required to be detected PSYO 1011 Psychophysics 2 • Method of Constant Stimuli o Amounts of a stimulus are presented on different trials o Participant reports if a stimulus was detected • Absolute Threshold o Lowest intensity at which a stimulus can be detected correctly 50% of the time  Lower the absolute threshold  ▯Greater the sensitivity The Method of Constant Stimuli & Absolute Threshold: • Example: Decibel level & response o Conduct experiment recording trial, decibel level & response o Summarize results in a table o Calculate percent w/ the formula  Yes response/Total trials o Chart results on a graph • Absolute Threshold o In example, intensity of stimulus detected 50% of the time was 9 db o Therefore, absolute threshold = 9 db Why is a Stimulus of a Particular Intensity Detected Sometimes but not Always? • Motivation • Attention • Ambient Noise • Internal Noise • Adaptation Level Signal Detection Theory: • Concept of fixed AT is inaccurate because of decision criterion o Individual standard of certainty that stimulus is present before confirmation of detection o Range of uncertainty  o Changes from 
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