Luc Geurts

Coding of the fundamental frequency in continuous interleaved sampling processors for cochlear implants

In this study the perception of the fundamental frequency (F0) of periodic stimuli by cochlear implant users is investigated. A widely used speech processor is the Continuous Interleaved Sampling (CIS) processor, for which the fundamental frequency appears as temporal fluctuations in the envelopes at the output. Three experiments with four users of the LAURA (Registered trade mark of Philips Hearing Implants, now Cochlear Technology Centre Europe) cochlear implant were carried out to examine the influence of the modulation depth of these envelope fluctuations on pitch discrimination. In the first experiment, the subjects were asked to discriminate between two SAM (sinusoidally amplitude modulated) pulse trains on a single electrode channel differing in modulation frequency ( deltaf = 20%). As expected, the results showed a decrease in the performance for smaller modulation depths. Optimal performance was reached for modulation depths between 20% and 99%, depending on subject, electrode channel, and modulation frequency. In the second experiment, the smallest noticeable difference in F0 of synthetic vowels was measured for three algorithms that differed in the obtained modulation depth at the output: the default CIS strategy, the CIS strategy in which the F0 fluctuations in the envelope were removed (FLAT CIS), and a third CIS strategy, which was especially designed to control and increase the depth of these fluctuations (F0 CIS). In general, performance was poorest for the FLAT CIS strategy, where changes in F0 are only apparent as changes of the average amplitude in the channel outputs. This emphasizes the importance of temporal coding of F0 in the speech envelope for pitch perception. No significantly better results were obtained for the F0 CIS strategy compared to the default CIS strategy, although the latter results in envelope modulation depths at which sub-optimal scores were obtained in some cases of the first experiment. This indicates that less modulation is needed if all channels are stimulated with synchronous F0 fluctuations. This hypothesis is confirmed in a third experiment where subjects performed significantly better in a pitch discrimination task with SAM pulse trains, if three channels were stimulated concurrently, as opposed to only one.

Enhancing the speech envelope of continuous interleaved sampling processors for cochlear implants

A new method to code the speech envelope in continuous interleaved sampling (CIS) processors for cochlear implants is proposed. In this enhanced envelope, the rapid adaptation seen in the response of auditory nerves to sound stimuli is incorporated. Two strategies, one using the standard envelope (CIS) and one using the enhanced envelope (EECIS), were tested perceptually with six postlingually deafened users of the LAURA cochlear implant. The tests included identification of stop consonants in three different vowel contexts and monosyllabic consonant-vowel-consonant (CVC) words. Significant improvements in correct identification scores were observed for stop consonants in intervocalic /a/ context (p = 0.026): average results varied from 46% correct for CIS to 55% for EECIS. This improvement was mainly due to the better transmission of place of articulation. The differences in identification scores for stop consonants in /i/ and /u/ context were not significant. The identification scores for the medial vowels of the CVC words were significantly higher when the EECIS strategy was used: average results increased from 39% correct to 46% correct (p = 0.018). No significant differences were observed between the results for initial and final consonants of the CVC words. The present results demonstrate that the inclusion of the rapid adaptation in the speech processing for cochlear implants can improve speech intelligibility.

The skweezee system: enabling the design and the programming of squeeze interactions

The Skweezee System is an easy, flexible and open system for designing and developing squeeze-based, gestural interactions. It consists of Skweezees, which are soft objects, filled with conductive padding, that can be deformed or squeezed by applying pressure. These objects contain a number of electrodes that are dispersed over the shape. The electrodes sense the shape shifting of the conductive filling by measuring the changing resistance between every possible pair of electrodes. In addition, the Skweezee System contains user-friendly software that allows end-users to define and to record their own squeeze gestures. These gestures are distinguished using a Support Vector Machine (SVM) classifier. In this paper we introduce the concept and the underlying technology of the Skweezee System and we demonstrate the robustness of the SVM based classifier via two experimental user studies. The results of these studies demonstrate accuracies of 81% (8 gestures, user-defined) to 97% (3 gestures, user-defined), with an accuracy of 90% for 7 pre-defined gestures.

A concept for a research tool for experiments with cochlear implant users

APEX, an acronym for computer Application for Psycho-Electrical eXperiments, is a user friendly tool used to conduct psychophysical experiments and to investigate new speech coding algorithms with cochlear implant users. Most common psychophysical experiments can be easily programmed and all stimuli can be easily created without any knowledge of computer programing. The pulsatile stimuli are composed off-line using custom-made MATLAB (Registered trademark of The Mathworks, Inc., http://www.mathworks.com) functions and are stored on hard disk or CD ROM. These functions convert either a speech signal into a pulse sequence or generate any sequence of pulses based on the parameters specified by the experimenter. The APEX personal computer (PC) software reads a text file which specifies the experiment and the stimuli, controls the experiment, delivers the stimuli to the subject through a digital signal processor (DSP) board, collects the responses via a computer mouse or a graphics tablet, and writes the results to the same file. At present, the APEX system is implemented for the LAURA (Registered trademark of Philips Hearing Implants) cochlear implant. However, the concept-and many parts of the system-is portable to any other device. Also, psycho-acoustical experiments can be conducted by presenting the stimuli acoustically through a sound card.

Splash controllers: game controllers involving the uncareful manipulation of water

In this paper we extend the field of organic user interfaces and introduce the Splash Controller. The main concept of a Splash Controller is that a user interacts with computing technology by manipulation of water in some kind of receptacle. To this end we highlight the possibilities of Splash Controllers, specifically as game controllers. Next, we specify a simple and robust technology for the detection of water. In order to demonstrate the feasibility of a Splash Controller, we additionally present the design and development of one specific Splash Controller prototype.

DYSL-X: Design of a tablet game for early risk detection of dyslexia in preschoolers

The goal of the DYSL-X project is to develop a tool to predict whether a preschooler (5 yrs) shows high risks for developing dyslexia. This tool is a tablet game that incorporates tests to take specific performance measures that allow for this prediction. The game will thus serve as an assessment tool to be used in school psychology services and clinical diagnostic and rehabilitation centers. In order to design the optimal tablet game for preschoolers, during the first phase of the projects several existing games for preschoolers were evaluated in order to derive design guidelines for games targeted at preschoolers. These design guidelines are presented in this paper and next, we show how these guidelines were used to develop the final game of the DYSL-X project.

Detection of small across-channel timing differences by cochlear implantees

Five post-lingually deafened users of the LAURA cochlear implant were presented with two trains of biphasic pulses applied concurrently to two widely separated channels. They could all discriminate between stimuli where pulses on the two channels were nearly synchronous (inter-channel delay=0.1 ms) and those where there was a longer delay applied to one channel. All showed an asymmetry, being more sensitive when the longer delay was on either the more basal or, depending on the listener, the more apical channel. For four out of the five listeners this asymmetry could be at least partly attributed to one stimulus, with a 0.1-ms delay in either the apical (three listeners) or basal (one listener) channel, sounding markedly different from all other stimuli used in the experiment. Both the overall sensitivity of listeners and the general pattern of results survived the presentation of maskers on intermediate channels, and did not vary markedly with changes in the polarity of the pulses applied to one channel. Although the results varied substantially across listeners, it is concluded that they demonstrate a genuine sensitivity to the relative timing of stimulation applied to discrete populations of auditory nerve fibers.

Game-based Assessment of Psycho-acoustic Thresholds: Not All Games Are Equal!

This paper first presents a critical analysis of an existing game (APEX), designed by researchers in psychoacoustics only, to measure psychoacoustic thresholds in preschoolers. Next it presents another game (DIESEL-X), designed by dyslexia researchers and game designers, to remediate the shortcomings of the former game. Via a repeated measures experiment (n = 95), the game experience, attention, and psychoacoustic thresholds are compared. It is shown that the children prefer the game experience of DIESEL-X over APEX. Moreover, the former game was able to measure lower frequency-modulation thresholds than APEX. These results demonstrate that when it comes down to game-based assessment of childrens perceptual capabilities, the quality of game design not only has an effect on game experience, but equally on the scientific measurements obtained via such a game-based assessment.

DIESEL-X: A Game-Based Tool for Early Risk Detection of Dyslexia in Preschoolers

DIESEL-X is a computer game that was developed to detect a high risk for developing dyslexia in preschoolers. The game includes three mini-games that test the player on three skills that are considered to yield outcome measures that predict the onset of dyslexia: the detection threshold of frequency modulated tones, a test on phonological awareness in which the player has to identify words that have the same phonetic ending, and a test on letter knowledge. In order to keep the motivation of the player high during testing, these tests are embedded in a computer game. We discuss the participatory design process that was adopted to design and develop the game, the rationale behind the design decisions, and we describe the resulting games.

Playfully learning visual perspective taking skills with sifteo cubes

In this paper we describe the design, development and testing of two computer games using Sifteo Cubes that help children to train their visual perspective taking (VPT) skills, i.e. the ability to see the world from another persons perspective. The challenge was to design an enjoyable and usable game that takes into account the huge variability in the perspective taking skills within the target group (preschoolers at the age of five, and older children with learning disabilities). Sifteo Cubes can be considered as digital or intelligent manipulatives that are often used in instruction. We advocate that these type tangible objects can help children performing VPT related tasks since they allow for actions in the real world that aid their thinking. Pre-test and post-test results revealed a short term learning effect on VPT skills after playing the two games.