Download and read the paper:

"Roughness perception of amplitude modulated tones is context dependent"
which you will find in the file "psychophysical.pdf" on the
course web page.

Your assignment is to understand and critique this paper. Here are
some specific questions that you may wish to answer to help in your
analysis of the paper:

(1) What is the physical correlate of "roughness"?

(2) The authors define the AM modulated signal s(t) on the first page.
Use Matlab (or your favorite computer language) to generate and 
plot a collection
of such signals for a variety of carrier and modulation frequencies
(f_c and f_m) and indices m. (Observe that the authors use p to mean
the constant pi). If you have a sound card, listen to the resulting waves
(in Matlab, use the "sound" command).

(3) For the plots generated in (2), find the magnitude spectrum.
(in matlab use abs(fft(s)) where s is the generated signal).
What is the relationship between the parameters f_c, f_m and m,
and the location of the spectral lines?

(4) Explain what the author means by the word "context."

(5) On page 8, the authors exclude a block of 27 trials. Why do you 
think they chose to exclude these?

(6) On page 9, the authors report several values of p (like p<.001,
p>.24). Explain what these p values are referring to. Why are they important?

(7) On page 11, the authors state "This difference in process 
difficulty between the 
two psychophysical methods can explain the observed discrepancies."
What does this mean? Explain the issue they are trying to resolve.
Do you think this methodological difference is an adequate explanation
for the observed differences? Why or why not?

(8) In experiment #2, the authors are testing the "same" thing as in experiment
#1, except the duration of the tones is different.
Go back to (2) and listen to the "same" signals you have generated but 
of different lengths. What perceptual differences do you hear?
If you must work from the plots alone, what differences do you see in
the spectra?

(9) Why did the authors chose to use a completely different set of 
listeners for experiment #2 than was used for experiment #1.
Was this choice sensible?

(10) The authors propose several ideas to explain why the results 
of experiments #1 and #2 differ. What are these explanations?
Given the way they have described their
experiments, can you think of any other possible explanations?

(11) On page 17, the authors "turn to the spectral domain" to explain
something. Discuss (a) what they are trying to explain in this paragraph.
(b) is their explanation accurate?
(c) is their explanation convincing?