The field of sonification has progressed greatly over the past twenty years and currently constitutes an established area of research. This article aims at exploiting and organizing the knowledge accumulated in previous experimental studies to build a foundation for future sonification works. A systematic review of these studies may reveal trends in sonification design, and therefore support the development of design guidelines. To this end, we have reviewed and analyzed 179 scientific publications related to sonification of physical quantities. Using a bottom-up approach, we set up a list of conceptual dimensions belonging to both physical and auditory domains. Mappings used in the reviewed works were identified, forming a database of 495 entries. Frequency of use was analyzed among these conceptual dimensions as well as higher-level categories. Results confirm two hypotheses formulated in a preliminary study: pitch is by far the most used auditory dimension in sonification applications, and spatial auditory dimensions are almost exclusively used to sonify kinematic quantities. To detect successful as well as unsuccessful sonification strategies, assessment of mapping efficiency conducted in the reviewed works was considered. Results show that a proper evaluation of sonification mappings is performed only in a marginal proportion of publications. Additional aspects of the publication database were investigated: historical distribution of sonification works is presented, projects are classified according to their primary function, and the sonic material used in the auditory display is discussed. Finally, a mapping-based approach for characterizing sonification is proposed.

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A systematic review of mapping strategies for the sonification of physical quantities.

The authors introduce a device for the parametric sonification of electroencephalographic (EEC) data. The device allows auditory feedback of multiple EEG characteristics in real time. Six frequency bands are assigned as instruments from a MIDI device. The time-dependent parameters modulate the timing, pitch, and volume of the instruments. Using this, we studied subjects' ability to perform a discrimination task with parametric sonification in real time.

Parametric orchestral sonification of EEG in real time

+ OBJECTIVE: To introduce a sound synthesis tool for human EEG rhythms that is applicable in real time.
+ METHODS: We design an event-based sonification which suppresses irregular background and highlights normal and pathologic rhythmic activity.
+ RESULTS: We generated sound examples with rhythms from well-known epileptic disorders and find stereotyped rhythmic auditory objects in single channel and stereo display from generalized spike-wave runs. For interictal activity, we were able to separate focal rhythms from background activity and thus enable the listener to perceive its frequency, duration, and intensity while monitoring. 
+ CONCLUSIONS: The proposed event-based sonification allows quick detection and identification of different types of rhythmic EEE events in real time and can thus be used to complement visual displays in monitoring and EEG feedback tasks.
+ SIGNIFICANCE: The significance of the work lies in the fact that it can be implemented for on-line monitoring of clinical EEG and for EEG feedback applications where continuous screen watching can be substituted or improved by the auditory information stream.

Supplementary Material for "Event-based sonification of EEG rhythms in real time"

Event-based sonification of EEG rhythms in real time

Sonification and textification: Proposing methods for classifying unspoken words from EEG signals

This paper presents techniques to render acoustic representations for EEG data. In our case, data are obtained from psycholinguistic experiments where subjects are exposed to three different conditions based on different auditory stimuli. The goal of this research is to uncover elements of neural processing correlated with high-level cognitive activity. Three sonifications are presented within this paper: spectral mapping sonification which offers a quite direct inspection of the recorded data, distance matrix sonification which allows to detect nonlinear long range correlations at high time resolution, and differential sonification which summarizes the comparison of EEG measurements under different conditions for each subject. This paper describes the techniques and presents sonification examples for experimental data.

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H. Bekel

Papers

Sonifications for eeg data analysis