• Background
  • Instructions
  • Stimulus Settings
  • Method Settings
  • Experiment
  • Results
  • Quiz

Background

The forced-choice methods were developed as a means to deal with problems associated with traditional psychophysical methods. In the traditional methods, participants can guess or even alter their response levels to appear more or less sensitive than they are, and the experimenter would not know. So, in forced-choice methods, the structure of the trial changes. In the most basic forced-choice experiment, the stimulus can be in one of two places or in one of two intervals. Then, instead of asking you if you see or hear the stimulus, you are asked where or when the stimulus occurred. If you do not know when or where the stimulus is, you have to guess. That is the forced in forced-choice.

In this experiment, the forced-choice is paired with a method of constant stimuli experiment. The way the stimuli are chosen follows the method of constant stimuli while the trials are run, according to forced-choice. This change leads to a bit of problem. In method of constant stimuli, the threshold is determined as the point where you detect the stimulus 50% of the time. Well, if you are guessing and there are only two options, when you cannot really detect the stimulus, you will be correct 50% of the time. To adjust for this issue, the threshold is determined as the stimulus intensity you correctly detect 75% of the time in a forced-choice experiment. To review method of constant stimuli, look here.