Comodulation masking release with signal-masker interactions represented 
in the envelope

Robert H. Pierzycki and Bernhard U. Seeber
MRC Institute of Hearing Research, Nottingham NG7 2RD, UK

In normal hearing, the threshold of a tone masked by a modulated narrow-band 
on-frequency masker (OFB) can be reduced if correlated modulation is present 
on spectrally distant flanking bands (FBs), an effect known as comodulation 
masking release (CMR). Since electric hearing with current cochlear implants 
is based on envelope information, comodulation of envelopes on multiple 
electrodes might also be beneficial for detection in electric hearing. 

CMR was investigated with normal hearing participants listening to unprocessed 
or vocoded stimuli. In Experiment 1, tone thresholds were determined when 
masked by a sinusoidally amplitude-modulated band of noise (SAM, OFB) and by 
zero to four FBs of noise whose envelopes were either co- or anti-modulated 
with the OFB envelope. In Experiment 2, envelopes of those signals were 
extracted in a vocoder and used to modulate noise or sinusoidal carriers, 
thereby replacing the original temporal fine structure (TFS). Significant CMR 
of 3-10 dB was found in unprocessed conditions and although reduced to 2-6 dB, 
CMR was still significant after vocoding. CMR did not differ significantly 
between the sine and the noise vocoder suggesting that the applied SAM 
determined the magnitude of CMR. Since CMR withstands vocoding, comodulation 
is hoped to improve detection in electric hearing. 



PACS:
43.66.Dc Masking

J. Acoust. Soc. Am. Volume 127, Issue 3, pp. 1808-1808 (March 2010) 
http://dx.doi.org/10.1121/1.3384101