A Developmental Study of Spatial Release from Masking of Lexical Tone Recognition in Mandarin-Speaking Children (General Research Fund, Research Grants council, 2016-2017)

Children’s learning through the auditory channel is optimal if the auditory signal is free from noise and competing sounds. However, children rarely learn in a quiet environment. Starting from their early preschool years they are exposed to complex auditory environments such as classrooms where a lot of learning takes place. Different competing sounds from various directions are simultaneously presented including the voices of adults and peers, environmental sounds and reverberation. The ability to segregate different acoustic streams coming from different directions, requiring complex computations that involve both monaural (one ear) and binaural (both ears) processing, is critical for children to selectively attend to important information out of the competing signals for speech and language learning. Children’s recognition of speech information in the presence of competing signals is degraded, when compared with that in quiet, this may severely affect auditory learning in everyday life (1-3). They need a higher signal-to-noise ratio in order to reach adult performance level (2, 4). One way to study auditory stream segregation is to see how well an individual improves from recognizing the target acoustic stream from (1) when it is spatially mixed with the competing acoustic stream, e.g. both coming from the front, to (2) when it is spatially separated from the competing acoustic stream, e.g. the target stream is coming from the front and the competing stream from one side, e.g. the left side. This improvement is called spatial release from masking (SRM). Consider the complexity of the neural processing for auditory stream segregation, there is no convincing evidence to suggest that children have already reached adult SRM level early in life. The study conducted by our team was one of the very first studies which found a clear development of SRM with age in young children which was recently published in the Journal of Speech, Language and Hearing Research (5). Our results showed that the developmental course of SRM in typically developing Mandarin-speaking children was indeed significantly longer than previous studies suggested, and the results are consistent with two different types of test materials. Therefore we propose a large scale developmental study to investigate the typical developmental trajectory of SRM in children and from which to delineate normal and disordered performance in SRM from preschool to mid elementary school years. Such a large scale developmental study is lacking in the international literature. This proposed study will contribute to the early identification of children who have a significantly weaker auditory stream segregation ability compared with their peers, revealed by SRM, which can lead to auditory processing, language, and other learning difficulties, so that timely interventions can be initiated. With the unique advantage of using lexical tones, which are acquired by age 2 or earlier, to test native Mandarin-speaking children, we will be able to investigate the development of SRM at a much earlier time window in children speaking tonal languages in this study than those speaking non-tonal languages from previous studies. SRM is baseline corrected by the difference between two data points obtained from the spatially separated and spatially mixed conditions, which can minimize the interference of linguistic knowledge, working memory, attention and task-related factors. Such a baseline correction makes SRM essentially a clean measure of sensory processing for spatial stream segregation, with those non-sensory factors teased out, to delineate individuals with normal and disordered SRM, and makes SRM potentially a universal auditory stream segregation test measure for cross-language comparisons.

Funding Source: RGC - General Research Fund (GRF)