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OVERVIEW

With this psychophysical method, you will compare a standard line of fixed length to a series of comparison lines of variable length. Your task is to judge whether the comparison (the bottom line) appears longer or shorter than the standard (the top line). By examining the graph showing the relation between the percentage of "longer than" responses and the size of the comparison stimuli, the point of subjective equality (PSE), the upper and lower thresholds (UT and LT), the size of the just noticeable difference (JND), and the interval of uncertainty (IU) are determined.

Objectives

  1. To gain practical experience with the method of constant stimuli.
  2. To understand how the data are analyzed with this method. You should be able to:
    1. determine the PSE using a graph
    2. determine the upper and lower thresholds (UT and LT) using a graph and
    3. calculate the JND.