To determine if critical bands, as determined by masking, are the same
for all frequencies.
To learn to test for limits.
To design your own experiment
Critical Bands - Review from material in class
Observations
How effectively a noise masks a tone depends not so much on the loudness
of the noise but the match between the frequencies of the noise and the
tone.
There is a region around the frequency that is trying to be detected
where noise can act as a masker.
Noise outside this band is ineffective as a masking stimulus.
Question: Are these critical bands always the same size for every
frequency?
Finding Limits
Below is our graph from the class critical bands experiment
Note how for the 1200 Hz tone, the masking stays about the same until the
frequency of the noise is less than 100 Hz.
This suggests that we can place that critical band at between 30 and 100
Hz.
This is a send of finding the limit or size of the critical band and an
example of what is needed to answer the question posed for th experiment.
In this experiment you will ask some question about critical bands.
You will be asked to design your own experiments to conduct this test.
Experimental Design
Experiments involve:
Independent Variable(s): the variable(s) the experimenter manipulates
Dependent Variable: the variable the experimenter measures
Control: Change only one thing at a time.
In this experiment, the IV and DV will be decided upon by you.
IVs: These will depend upon the question that you want to ask.
DV: this depends upon what you need to observer and the method that you
use.
Your task is to develop this experiment so that you can learn something
about critical bands.
Your design can be adjusted as you go to make sure you get a good answer,
though you need a well structured experiment to begin with.
This freedom is often part of research in many areas of science.
However, in many psychology experiments, all of the conditions have to be
set up before the data collection begins because of the nature of testing
groups of subjects.
Since psychophysics tests individuals, and the few of you are easily
recollected, you can make some adjustments on the fly.
The inability to answer the question of this lab report will lead to a
significant negative impact on the grade for this lab. Remember you
may need to add new conditions to test. Give yourself and your
partners time.
The Experiment:
Equipment
Back to the Experiencing Sensation and Perception Software
There are headphones available as well. You will want to use them in
your rooms if you have any. In lab you many need them to keep the sounds
straight.
Common Design Elements:
Here are the common settings on the Experimental Parameters Page that
everyone will use:
Type of Activity: Experiment
Variable Design Elements:
Any of the stimulus parameters on the stimulus setup page for the
experiment.
These will depend upon your experimental design.
Chose them to try to see clearly what is going on in the data
Adding new conditions is one way to clarify your findings
The experimental method
You can choose:
Method of Limits,
Method of Constant Stimuli, or
Method of Adjustment
The settings for the method
Choose the method that allows for clear results.
Too easy can allow for sloppy results
Too hard can cause fatigue which can mess up your results without taking
breaks
Do not under/over collect data.
You will work in a group of 3-4 to design your experiment. I will
assign people.
Procedure:
Most will depend upon the nature of your experiment.
There are some common element:
The top graph shows the tone.
The bottom graph shows the noise.
At the bottom of the screen are the response buttons: The response buttons
will depend upon the method. Instructions will be displayed there.
Data
Convert the gain measures you get out of the computer program to decibels