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Lecture 2

# Lecture 2.docx

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School
Western University
Department
Psychology
Course
Psychology 2115A/B
Professor
Prof
Semester
Winter

Description
Lecture Two: Psychophysics 9/12/2012 11:34:00 AM Gustave Fechner- father of psychophysics There are two questions:  1. What is the minimum amount of intensity that the stimulus needs to have until you can sense the stimulus- Detection o this is called the absolute threshold  2. Minimum difference needed to perceive two different stimulus- Discrimination o The just noticeable difference o “ the JND” Detection  Able to test for the absolute threshold by graphing the probability that you will react to a stimulus given, the probability will stay zero until you react to the stimulus, thus crossing the absolute threshold  Fechner came up with two ideas o 1. The method of limits: you take a stimulus, weak intensity- subject will most likely say that they have not perceived it. Over time slightly increase the stimulus until the subject perceives that stimulus (crossed the absolute threshold)  Always alternate series, starting from hearing the stimulus until you cant, and then starting from not being able to hear the stimulus until you can  Errors of perseveration: will say no or yes longer then they should (keeps going)  Errors of anticipation: anticipate the change and say yes or no too soon  Vary starting point: Don’t start at the same place so they don’t fall into a habit (say three yes, one know and continue with that)  After all the trials get and average ascending and average descending- average the two and gets the absolute threshold  2. The method of constant stimuli: Take ten stimulus, some above the threshold and some below the threshold, and randomly present them to the subject 20 times. o Random noise in your internal system with a high intensity stimulus will cause a false positive (thinking that you can here the noise) o If your internal system is low with a low intensity, the probability of saying yes o Find the point on the graph were fifty percent of the time you say yes and the other half of the time you say no Discrimination  The standard stimulus will stay the same throughout the experiment –MUST BE  The standard wil
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