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Lecture 4

PSY 3108 Lecture Notes - Lecture 4: Semi-Log Plot, Scatter Plot, Doubleclick

Course Code
PSY 3108
Charles Collin

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(graded out of 50, worth 5% of final grade)
This lab consists of a single part, which should be done at home. If you wish to do
the lab in the lab room, you will need to bring headphones.
For this lab, you will need the following:
- A computer capable of playing sound. It is best if you use reasonably high
quality headphones or speakers, but just use the built in speakers if
necessary (though they are typically of poor quality)
- A program capable of playing .WAV files (almost any modern computer will
have such software).
- A set of .wav files that each plays a given frequency of pure tone in a
descending sequence of amplitudes (we have provided you with this).
If you do not have access to the necessary hardware and/or software, you may use
the computers in the lab room, but in this case you must bring a set of headphones
(ear buds, etc.)
Handing In: Hand in your lab as follows:
1. Fill out this document in the spaces provided
2. Save it as "Lab4YourNameStudent#.docx"
(e.g., Lab4CharlesCollin123456.docx). It's okay if it's .doc format.
3. Send it via email to the following address:
4. Use the subject line: PSY3108X Lab4, YourName StudentNumber
(e.g., PSY3108A Lab4, Charles Collin 123456)
Failure to follow these instructions properly will lead to a 10% mark deduction, so
be careful!
If, for some reason, you cannot submit your lab electronically, then you may submit
a paper copy instead. Email the TA to let her know that you will be doing this.
Background: In class we discussed the idea that there are two fundamental
characteristics of sound: Frequency and Amplitude. In previous classes we
discussed how absolute thresholds for one sensory dimension often depend upon
another (e.g., the threshold for tactile pressure depends on the vibration speed of
the probe). Here we will examine how the absolute threshold for sound amplitude
varies as a function of sound frequency. As we will see in the next chapter, this
function is a fundamental characteristic of the human auditory system. The fact that
amplitude varies with frequency is important to, among other things, sound
illusions. In preparation for this lab, you should read Chapter 5, esp. sections A2 and
B2. You may also want to read ahead into Chapter 6, esp. section A1.
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Procedure: You will be acting as researcher and participant for this lab. There is no
need for a partner.
What you will be doing in this lab is playing a series of sound files (e.g.,
HumBeh_p007_200Hz.wav). Each sound file plays a series of pure tones at a given
frequency. The tones drop in amplitude. You will be counting the number of tones
you can hear for each file and deducing from that what your absolute amplitude
threshold is for each frequency.
Here are the detailed instructions:
1) Adjust the volume on your computer for proper playback of the tones.
a) Use the best quality audio headphones or speakers available. If you use low
quality ones, you will find that some of the files, especially at the low
frequency end, produce no sound when you play them. This is because these
tones are outside the range of frequencies your speakers can produce. If this
occurs, simply mark "N/A" for the data for that frequency and plot the
function for the values that you can play. Even cheap speakers should be
able to play 200 Hz and above.
b) Do your measurements in the quietest room available. Background noises
will interfere with the sounds you are trying to hear, and may change your
threshold values. If you do the measurements in the lab room, be sure to use
c) Repeatedly play the 3500 Hz sequence (file name:
HumBeh_p007_3500Hz.wav) and adjust the volume so that you hear only the
first 18 tones in the sequence. There are 25 tones in the file, so this means
that you have adjusted the volume so that tones 1925 are below your
threshold of hearing.
d) Leave the volume setting at this level for all of the other files.
2) Listen to each file and count the number of tones you can hear.
a) Repeat at least five times for each file to assure an accurate count. You should
do this in some kind of random order (how you implement this is up to you).
b) Use the table in the results section to keep track of your counts.
c) Allow yourself about an hour for this step.
3) Convert your count to a threshold value for each frequency.
a) You will be plotting your results relative to your threshold for the 3500 Hz
tone sequence. We will assign 3500 Hz to 0 dB. Note that our measurements
here are necessarily relative to some standard, as we have not calibrated our
speakers to determine exactly what amplitudes are actually being played.
b) To calculate your threshold value for a given frequency, take the average
count for that frequency, subtract it from your count for 3500 Hz, and
multiply this number by 3 dB (because each tone in the sequence is
decremented in amplitude by 3 dB).
c) For example, let's say for the 100 Hz tone you counted 5, 6, 4, 7, and 3 tones
on the five runs for that file. This averages to 5. So you counted an average of
5 levels for the 100 Hz tone sequence. Your threshold for 100 Hz would then
be: 18 − 5 × 3 = 39 dB
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