The term "biometric art" has been proposed to describe art derived from physiological measurements of living organisms [1,2]. While the term was coined to describe visual representations of cardiac activity and other physiological functions, it can also be extended to auditory representations. In a complementary manner, a number of composers have explored applications of complexity ("chaos") theory to music composition and synthesis [3]. Heart rhythms have also been used in musical contexts [4,5], and experiments have even been conducted that have mapped real-time heart rhythms to brief auditory displays for use in biofeedback [6]. This project, however, has a different focus. Rather than setting out to create musically interesting sounds, we explore whether physiological variations in heart rate dynamics over a period of hours could be a source of medically useful representations. In other words, can bedside diagnosis be aided by information taken from an auditory display of human heart rate variability? HEART RATE VARIABILITYHeart rate uctuations can be easily measured from an electrocardiogram (ECG), a graphical recording of the electrical potentials generated by cardiac muscle cells. While clinicians often refer to the healthy heartbeat as "regular sinus rhythm," healthy subjects typically display patterns more complex than those found in unhealthy ones [7][8][9]. For example, researchers have found that patients whose heart rates become overly regular following a heart attack may be at increased risk of fatal cardiac arrhythmias [10]. This loss of variability may be related to a decrease in the plasticity of the neural mechanisms that help regulate and " ne-tune" the heart's activity on a beat-tobeat basis. A fuller understanding of the dynamics of these kinds of cardiac signals in health and disease is the goal of contemporary heart rate variability research [11].To measure heart rate over extended periods, physicians make use of Holter monitors, ECG devices that permit long-term ambulatory recording and storage of ECG waveforms for time periods on the order of 24 hours. Following the recording, the data can be processed via automated or semi-automated programs. Such programs detect the electrical pulses, termed QRS complexes, that trigger mechanical contraction of the heart's pumping chambers (ventricles). Further analysis of these waveforms can be used to generate a sequence of intervals (the intervals between QRS complexes, also called "NN intervals" or "RR intervals," shown in Fig. 1) that represent the time periods between consecutive normal beats. These NN intervals, representing heart rate uctuations, are the datasets most often used in heart rate variability analysis.The heart's normal beats are initiated by impulses from pacemaker cells in the sinus node, hence the term normal sinus rhythm. The sinus node frequency is modulated primarily by input from the autonomic (involuntary) nervous system. There are two major components of this system: the sympa-

This paper is a study of the unique problems posed by the use of computers by composers and performers of music. The paper begins with a presentation of the basic concepts involved in the musical interaction with computer devices, followed by a detailed discussion of three musical tasks: music manuscript preparation, music language interfaces for composition, and real-time performance interaction. Fundamental design principles are exposed through an examination of several early computer music systems, especially the Structured Sound Synthesis Project. A survey of numerous systems, based on the following categories, is presented: compositions and synthesis languages, graphics score editing, performance instruments, digital audio processing tools, and computeraided instruction in music systems. An extensive reference list is provided for further study in the field.

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Publication details, including instructions for authors and subscription information: ABSTRACT Music: Old Problems, New SolutionsThis paper presents some observations on certain fundamental issues associated with the presentation of music which combines performers and electronically generated and processed signals delivered by loudspeakers. I contend that several factors have limited the growth of the genre and will attempt to illustrate their origins and consequences. These comments lead to some general recommendations to correct the situation and to some observations from my own experiences as a composer and performer. Finally, I examine a few new technologies which may soon impact the genre.

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