Information theoretic evaluation of a noiseband-based cochlear implant simulator

Noise-band vocoders are often used to simulate the signal processing algorithms used in cochlear implants (CIs), producing acoustic stimuli that may be presented to normal hearing (NH) subjects. Such evaluations may obviate the heterogeneity of CI user populations, achieving greater experimental control than when testing on CI subjects. However, it remains an open question whether advancements in algorithms developed on NH subjects using a simulator will necessarily improve performance in CI users. This study assessed the similarity in vowel identification of CI subjects and NH subjects using an 8-channel noise-band vocoder simulator configured to match input and output frequencies or to mimic output after a basalward shift of input frequencies. Under each stimulus condition, NH subjects performed the task both with and without feedback/training. Similarity of NH subjects to CI users was evaluated using correct identification rates and information theoretic approaches. Feedback/training produced higher rates of correct identification, as expected, but also resulted in error patterns that were closer to those of the CI users. Further evaluation remains necessary to determine how patterns of confusion at the token level are affected by the various parameters in CI simulators, providing insight into how a true CI simulation may be developed to facilitate more rapid prototyping and testing of novel CI signal processing and electrical stimulation strategies

Measurement and analysis of perceptual coding in the human auditory system: Multi-modal studies using neural activation patterns

A framework is presented for measuring perceptual differences among auditory scenarios and for producing target perceptual effects in auditory experiments. Auditory scenarios are specific configurations of auditory sub-systems, including both hearing loss due to physiological impairment and/or augmentation via a prosthetic device (e.g., the cochlear implant). The framework is developed around comparisons between scenarios at the level of the auditory nerve, which encapsulates the effects of many forms of hearing loss and device augmentations (e.g., the cochlear implant stimulates the auditory nerve directly from within the cochlea). At the auditory nerve, neural activation is viewed as a pattern in both space (the distance along the cochlea) and time. These patterns are generated by forward models that represent the acoustic pathways for various scenarios leading to the auditory nerve. Thus, a neural activation pattern completely encodes an auditory input and a specific auditory scenario. After generating two such patterns, the framework applies a special transformation and then computes the perceptual difference with a special measurement. The transformation and measurement are both developed within this framework for mapping unit perceptual differences to measurable unit distances. Two forward models are also developed within this work and presented for specialized use alongside a growing body of modeling work. Using the framework, results are presented that demonstrate potential shortcomings in current acoustic representations of the cochlear implant for normal-hearing subjects

Familiarity and Pronounceability of Nouns and Names

Ratings of familiarity and pronounceability were obtained from a random sample of 199 surnames (selected from over 80,000 entries in the Purdue University phone book) and 199 nouns (from the Kučera-Francis, 1967, word database). The distributions of ratings for nouns versus names are substantially different: Nouns were rated as more familiar and easier to pronounce than surnames. Frequency and familiarity were more closely related in the proper name pool than the word pool, although both correlations were modest. Ratings of familiarity and pronounceability were highly related for both groups. A production experiment showed that rated pronounceability was highly related to the time taken to produce a name. These data confirm the common belief that there are differences in the statistical and distributional properties of words as compared to proper names. The value of using frequency and the ratings of familiarity and pronounceability for predicting variations in actual pronunciations of words and names are discussed