This study investigated whether the McGurk effect breaks down if the duration of the target consonant is substantially extended beyond the durations occurring in normal speech. It was found that the McGurk effect persisted without diminishing in strength up to the maximum duration tested of 3.9 seconds.
Bibliographic reference. Kroos, Christian / Dreves, Ashlie (2008): "Does the Mcgurk effect rely on processing time constraints?", In INTERSPEECH-2008, 528.