Phonetic and lexical interferences in informational masking during speech-in-speech comprehension

This study investigates masking effects occurring during speech comprehension in the presence of concurrent speech signals. We examined the differential effects of acoustic-phonetic and lexical content of 4- to 8-talker babble (natural speech) or babble-like noise (reversed speech) on word identification. Behavioral results show a monotonic decrease in speech comprehension rates with an increasing number of simultaneous talkers in the reversed condition. Similar results are obtained with natural speech except for the 4-talker babble situations. An original signal analysis is then proposed to evaluate the spectro-temporal saturation of composite multitalker babble. Results from this analysis show a monotonic increase in spectro-temporal saturation with an increasing number of simultaneous talkers, for both natural and reversed speech. This suggests that informational masking consists of at least acoustic-phonetic masking which is fairly similar in the reversed and natural conditions and lexical masking which is present only with natural babble. Both effects depend on the number of talkers in the background babble. In particular, results confirm that lexical masking occurs only when some words in the babble are detectable, i.e. for a low number of talkers, such as 4, and diminishes with more talkers. These results suggest that different levels of linguistic information can be extracted from background babble and cause different types of linguistic competition for target-word identification. The use of this paradigm by psycholinguists could be of primary interest in detailing the various information types competing during lexical access.