Look about the room you are in and think about what you are perceiving.
How confident are you in your perceptions?
Are you quite certain that you are seeing a computer in front of you?
Our intuitions suggest abrupt thresholds--you either perceive something or you do not. If this is true, than a discrimination function for detecting a change in frequency, which we perceive as pitch, would look like the graph to the right. A discrimination task asks the participant to say whether or not two stimuli, in this case tones, are the same or different. "Same" responses are recorded as 0, "different" responses as 1. If perception is indeed binary and discreet, than a sudden shift would occur. In other words, you would quite suddenly hear that the two tones were different. Is this truly the case? To examine this, participate in the following discrimination task using three different tones. Will your perception be sudden, allowing you to tell absolutely and reliably when a change occurs between tone 1 and tone 2?
Listen to the trials as many times as you like, and then check whether the two tones are the same or different. When you are comfortable with the task, feel free to listen only once to each trial. After you complete each set, press the "Register" button beside the table to view your results. Don't worry about saying "same" or "different" an equal number of times, just mark whether or you not you hear the tones as the same, or different. Once you have completed the discrimination task at all three frequencies, you will be graphing your responses as a function of frequency (details to follow task).
To graph your responses, you will need to copy and paste each column into the graphing program of your choice. For each JND task, the first column contains the physical change presented (in Hz) and the second column records how many times you said that the two tones were the "different" (out of three possible). The data are presented sorted by physical change, not in the order you responded. The steady tone for the Medium frequency was 440 Hz, for the High frequency was 1760 Hz, and was 110 Hz for the low frequency.
Graph your responses as a function of the physical difference.
Discuss whether or not your discrimination functions match our intuitive prediction (see top of page).
Discuss similarities and differences of the discrimination functions among the frequencies.