PSYC 230 Assignment (Tritone Paradox)
Name: ______R:______
Background: Shepard tones are musical notes that include the sine-wave frequencies in all octaves of a music note (A, A#, B, C, C#, D, D#, E, F, F#, G, and G#). When played in succession on a chromatic scale, a Shepard tone will always sound higher in pitch than the Shepard tones preceding it and will always sound lower in pitch than the Shepard tones that follow. Hence, there is a bit of circularity to a musical scale that is played with Shepard tones. Specifically, Shepard tones can be arranged on a circular pitch-class scale .
A tritone is any pair of notes on opposite sides of a pitch-class scale (e.g., C-F#, C#-G); whereas a semitone is any non-opposite pair of notes (e.g., C-C#, C-B). If notes in a tritone are played in succession, it is difficult to tell whether the two tones ascend in pitch or descend in pitch; whereas the pitch -change (ascending or descending) for semitones is easy to detect. Interestingly, while one person may hear a particular tritone ascend in pitch, another person may hear it descend. Thus, the pitch class scale is unique for each individual; with the note at the top representing the first note in a tritone that a person most often hears descending in pitch.
Purpose: To familiarize you with auditory perception and pitch changes by constructing your own pitch class circle. A discussion of the tritone illusion is here http://philomel.com/musical_illusions/tritone.php
Task: You will use the PsyCog CD for this assignment. Before beginning the task, check out demo B1.1, which presents the infinite scale illusion using Shepard tones. Next, check out demo B1.4 to see what tritones sound like. When you are ready, begin the Triton Paradox experiment (B1.2a), by following the instructions here and on the CD.
On each trial, you will her the two Shepard tone notes in a tritone pair played in succession. Some pairs will sound as through the pair is ascending in pitch, others will sound as though the pair is descending in pitch. Your task is to decide whether the second tone in each pair sounds higher in pitch or lower in pitch than the first tone. There really is no right or wrong answer, just listen carefully and respond appropriately.
Data Analysis: Your data will be somewhat analyzed already. The CD will construct a graph with the tritone pairs on the x-axis (the first note in each pair is the tone played first), and the percentage of times that you heard each tritone pair descending in pitch on the y-axis. Included in the graph will be your own pitch class circle. (I have found that the pitch-class circle may not be oriented correctly sometimes.) Print out your results and hand them in in with this assignment, and then answer the following:
1) Which tritone pair did you most often hear descend in pitch? (Use result from the graph.)
PSYC 230 Assignment (Tritone Paradox)
2) Why do you think that pitch class scale differs across people? That is, what are some factors that might affect the orientation of the pitch class scale?
3) Why do you think perception of the pitch change in a tritone is ambiguous and difficult to identify, but the pitch change in a semitone (e.g., C-D) is easy to detect? What is it about a tritone that leads to this ambiguity?