C Ludvigsen

Bio: C Ludvigsen is an academic researcher. The author has contributed to research in topics: Background noise & Noise. The author has an hindex of 1, co-authored 1 publications receiving 241 citations.

ICRA noises: artificial noise signals with speech-like spectral and temporal properties for hearing instrument assessment. International Collegium for Rehabilitative Audiology.

Abstract: Current standards involving technical specification of hearing aids provide limited possibilities for assessing the influence of the spectral and temporal characteristics of the input signal, and these characteristics have a significant effect on the output signal of many recent types of hearing aids. This is particularly true of digital hearing instruments, which typically include non-linear amplification in multiple channels. Furthermore, these instruments often incorporate additional non-linear functions such as "noise reduction" and "feedback cancellation". The output signal produced by a non-linear hearing instrument relates to the characteristics of the input signal in a complex manner. Therefore, the choice of input signal significantly influences the outcome of any acoustic or psychophysical assessment of a non-linear hearing instrument. For this reason, the International Collegium for Rehabilitative Audiology (ICRA) has introduced a collection of noise signals that can be used for hearing aid testing (including real-ear measurements) and psychophysical evaluation. This paper describes the design criteria, the realisation process, and the final selection of nine test signals on a CD. Also, the spectral and temporal characteristics of these signals are documented. The ICRA noises provide a well-specified set of speech-like noises with spectra shaped according to gender and vocal effort, and with different amounts of speech modulation simulating one or more speakers. These noises can be applied as well-specified background noise in psychophysical experiments. They can also serve as test signals for the evaluation of digital hearing aids with noise reduction. It is demonstrated that the ICRA noises show the effectiveness of the noise reduction schemes. Based on these initial measurements, some initial steps are proposed to develop a standard method of technical specification of noise reduction based on the modulation characteristics. For this purpose, the sensitivity of different noise reduction schemes is compared by measurements with ICRA noises with a varying ratio between unmodulated and modulated test signals: a modulated-unmodulated ratio. It can be anticipated that this information is important to understand the differences between the different implementations of noise reduction schemes in different hearing aid models and makes.

Are individual differences in speech reception related to individual differences in cognitive ability? A survey of twenty experimental studies with normal and hearing-impaired adults

Abstract: This paper summarizes twenty studies, published since 1989, that have measured experimentally the relationship between speech recognition in noise and some aspect of cognition, using statistical techniques such as correlation or factor analysis. The results demonstrate that there is a link, but it is secondary to the predictive effects of hearing loss, and it is somewhat mixed across study. No one cognitive test always gave a significant result, but measures of working memory (especially reading span) were mostly effective, whereas measures of general ability, such as IQ, were mostly ineffective. Some of the studies included aided listening, and two reported the benefits from aided listening: again mixed results were found, and in some circumstances cognition was a useful predictor of hearing-aid benefit.

An Algorithm for Predicting the Intelligibility of Speech Masked by Modulated Noise Maskers

Abstract: Intelligibility listening tests are necessary during development and evaluation of speech processing algorithms, despite the fact that they are expensive and time consuming. In this paper, we propose a monaural intelligibility prediction algorithm, which has the potential of replacing some of these listening tests. The proposed algorithm shows similarities to the short-time objective intelligibility STOI algorithm, but works for a larger range of input signals. In contrast to STOI, extended STOI ESTOI does not assume mutual independence between frequency bands. ESTOI also incorporates spectral correlation by comparing complete 400ms length spectrograms of the noisy/processed speech and the clean speech signals. As a consequence, ESTOI is also able to accurately predict the intelligibility of speech contaminated by temporally highly modulated noise sources in addition to noisy signals processed with time-frequency weighting. We show that ESTOI can be interpreted in terms of an orthogonal decomposition of short-time spectrograms into intelligibility subspaces, i.e., a ranking of spectrogram features according to their importance to intelligibility. A free MATLAB implementation of the algorithm is available for noncommercial use at http://kom.aau.dk/~jje/.

Development and analysis of an International Speech Test Signal (ISTS)

Abstract: For analysing the processing of speech by a hearing instrument, a standard test signal is necessary which allows for reproducible measurement conditions, and which features as many of the m...

Dyslexia and the failure to form a perceptual anchor.

Abstract: In a large subgroup of dyslexic individuals (D-LDs), reading difficulties are part of a broader learning and language disability. Recent studies indicate that D-LDs perform poorly in many psychoacoustic tasks compared with individuals with normal reading ability. We found that D-LDs perform as well as normal readers in speech perception in noise and in a difficult tone comparison task. However, their performance did not improve when these same tasks were performed with a smaller stimulus set. In contrast to normal readers, they did not benefit from stimulus-specific repetitions, suggesting that they have difficulties forming perceptual anchors. These findings are inconsistent with previously suggested static models of dyslexia. Instead, we propose that D-LDs' core deficit is a general difficulty in dynamically constructing stimulus-specific predictions, deriving from deficient stimulus-specific adaptation mechanisms. This hypothesis provides a direct link between D-LDs' high-level difficulties and mechanisms at the level of specific neuronal circuits.

Benefits from hearing aids in relation to the interaction between the user and the environment.

Abstract: It is becoming increasingly recognized that, in addition to the influence of audiometric variables and associated psychoacoustic abilities, the benefits from and candidature for various signal-processing schemes in hearing aids are strongly influenced by listeners' characteristics (such as motivations, expectations, and personality), and also the auditory environments in which those listeners are required to function (i.e. their auditory ecology). We will report elsewhere an experiment on a group of 50 listeners in a within-subject, randomized, blind, crossover design of five different hearing aid rationales, of which two contained linear amplification and three contained non-linear amplification which differed only in release-time constant. This article reports the interaction between the audiometric and cognitive characteristics of listeners, and the test conditions under which speech identification procedures are conducted (presentation level, signal-to-noise ratio, and temporal characteristics of inte...