If reversing chunks, (i.e. playing backwards), modifies the speech too much , try chopping between the original and a time-shifted duplicate …
done using Robert J.H’s chopper code … automated silence interval - #9 by Robert_J_H
[ I christened this process Unwinisation 
]
The “PaulStretch” effect in Audacity will temporally (horizontally) blur the sound spectrogram :
the result is like very severe reverberation …
“Sine speech” may applicable , but people can learn to understand it …
http://www.lifesci.sussex.ac.uk/home/Chris_Darwin/SWS/
http://www.scholarpedia.org/article/Sine-wave_speech