Does anybody recognize the origin of this picture?

[Pulkki Ville <ville.pulkki@xxxxxxxx>]

Hello,

I am translating into English (and also updating and broadening the scope)
the Finnish book by late Matti Karjalainen on communication acoustics. It
will be an introduction various topics in  audio, speech, technical
audiology and psychoacoustics, meant for e.g. Msc-level teaching in
technical universities. Wiley will publish it, hopefully in autumn. There
will be about 250 figures and 430 pages.

The Finnish book did not mention the origins of the figures. I have
been able to find about 100 figures from different papers and books, but I
can not find a single figure from anywhere. It is a listening test result
about pre- and post-masking thresholds for an impulse probe caused by an
impulse masker. 
In the test the subject has heard a sequence of masking impulses (e.g.
with 50 Hz rate), and a test impulse has been presented before or after
the masking impulse, and the threshold of audibility has been measured for
the test impulse. The figure is here:

http://www.acoustics.hut.fi/u/ville/impulse-masking.png

Any ponters would be appreciated.

Grateful for your help!

Best, 
Ville Pulkki
Ville.Pulkki@xxxxxxxx
Tenure track assistant professor
Department of Signal Processing and Acoustics
School of electrical engineering
Aalto University