Projects
Title: Auditory and cognitive effects on the intelligibility of speech in noise (WC2008-048)
Background
People’s ability to understand speech in adverse listening conditions like noisy environments can only partly be explained by their auditory functioning. This is especially apparent for hearing impaired people. There is rising evidence that speech understanding is also determined by people’s cognitive capabilities. Some cognitive functions that appear to be relevant for processing speech are general language skills and operations related to working memory. However, the individual contributions of auditory and cognitive factors are not yet completely understood.
Objectives
The main objective of this study is to increase current insights into the role of both hearing and cognition in understanding speech in noise, particularly for hearing impaired people. Also, the influence of the factor age is examined. The findings will help to increase the effectiveness of hearing rehabilitation by providing background information for ways of rehabilitation complementary to existing methods, i.e., hearing aids.
Furthermore, we strive to develop a clinically applicable test for screening of the cognitive abilities involved in speech understanding.
Method
We conduct several studies with both normal hearing and hearing impaired adult study subjects of all age groups. We measure hearing abilities in terms of pure tone hearing threshold, speech reception threshold, and spectral and temporal resolution. Cognitive functioning is addressed with a focus on processing speed and verbal working memory capacity. Furthermore, general linguistic abilities are assessed, such as lexicon accessibility and size. We use available tests that are well established and evaluated for their test domain and tests that have been developed at our department to complement shortcomings of the existing tests.
Study 1
The first study of the project was dedicated to identifying a visual test that gives a general account of the cognitive abilities involved in speech understanding. The original version of the test was developed at our department in a previous PhD project. We evaluated several new versions along with auditory tests for speech understanding in noise and tests for working memory capacity and cognitive processing speed. The study was conducted with normal hearing subjects to avoid any confounding by hearing impairment. The study participants were from a large age range of 18-78 years.
The study successfully identified one of the new test versions as a good measure of the cognitive contributions to speech understanding. The test was able to explain a good deal of the variance in speech understanding observed in the normal-hearing study sample. Importantly, the performance on the test was only marginally influenced by age. Performance on the other cognitive tests on the other hand was strongly age-dependent. Cognitive influences on speech understanding were generally bigger in fluctuating backgrund noise than in steady-state noise. An article reporting the findings from this study has been accepted for publication in the Journal of Speech, Language, and Hearing Research, see Publications.
Study 2
Previous research has shown that speech-comprehension abilities can be influenced by individual differences in working-memory (WM) capacity. Traditionally, so-called span tests are used to measure WM capacity. These tests typically include a primary memory task and an additional secondary task, which functions to increase the processing loas during the primary task. The objective of the second study was to develop new Dutch tests of WM capacity, which can be used for both auditory and vidual measuring of WM capacity. Young normal-hearing study participants performed the new tests along with tests for speech comprehension in noise and the above-mentioned visual test for cognitive skills contributing to speech comprehension. The study results indicated that the new tests are reliable measures of WM capacity and can be further applied in cognitive hearing research. An article describing the study has been submitted to a scientific journal.
Study 3
The third study is currently in preparation and will investigate cognitive and auditory temporal influences on speech comprehension.
Project leader
Prof J.M. Festen, VUmc
Project Members
Jana Besser, MSc, VUmc
S.E. Kramer, PhD, VUmc
S.T. Goverts, PhD, VUmc