The ubiquitous nature of communication in computer networks, firmly manifested in the Internet era, provided a context for the introduction of different collaborative tools widely accepted by the on-line community, such as textual chats, white boards, shared editors, video conference systems, shared spaces for the exchange of multimedia documents or even simple e-mail based collaborative systems.

Multi-user UNIX-like operating systems such as Linux are often considered unsuitable for real-time data collection because of the potential for indeter-minate timing latencies resulting from preemptive scheduling. In this paper, Linux is shown to be fully adequate for precisely controlled programming with millisecond resolution or better. The Linux system calls that subserve such timing control are described and tested, and then utilized in a MIDI-based program for tapping and music performance experiments. The timing of this program, including data input and output, is shown to be accurate at the millisecond level. This demonstrates that Linux, with proper pro-gramming, is suitable for real-time experiment software. In addition, the detailed description and test of both the operating system facilities and the application program itself may serve as a model for publicly documenting programming methods and software performance on other operating sys-tems.

In this study we report on an experiment in which listeners were asked to tap in time with expressively performed music, and compare the results to two other experiments using the same stimuli which investigated beat and tempo perception through other modalities. Many computational models of beat tracking assume that beats correspond with the onset of musical notes; we consider the hypothesis that the beat times are rather given by a curve that is "smoother" than the tempo curve of the note onset times, which nevertheless can be derived from the onset times. The tapping results show a tendency to underestimate the tempo changes, which supports the smoothing hypothesis, and agrees with listening experiments and other tapping studies.

Zero--lag synchrony arises between two points on the cerebral cortex when these receive concurrent independent inputs and has generally been ascribed to nonlinear mechanisms. We report results obtained by Principal Component Analysis (PCA) applied to simulations of cerebral cortex which exhibit zero--lag synchrony and realistic spectral content, and show that synchrony can arise by distinct and separable linear and nonlinear mechanisms. For lower levels of cortical activation synchrony between the sites of input can be accounted for by the eigenmodes associated with the wave activity generated by the inputs. The first spatial eigenmode arises from even 2 Clare L. Chapman et al. components in the independent input signals and the second spatial eigenmode arises from odd components in the inputs. Together these account for most of the signal variance, while the predominance of the first mode over the second within the near--field of the inputs accounts for zero--lag synchrony in the ne...

1A Experimental paradigm 1B Evidence for a central timing mechanism 635 2 Independent-Channels Model 2A The general model

We address the perception of small onset asynchronies as typically found in expressive piano performance (melody lead), which is associated with differences in hammer velocity and hence loudness or salience of chord tones. In three experiments, 26 musicians heard harmonic major-sixth dyads with both tones in the range B4 to Bb5. The tones in each dyad were either both pure, both sawtooth, or both recorded acoustic piano; and either synchronous or asynchronous. First, participants adjusted the relative level of the two tones until they sounded equally loud. This resulted in roughly equal SPL for pure and piano tones, but in the sawtooth tones the higher tone was typically 6 dB more intense, possibly due to simultaneous masking among the partials. In the next experiment, the relative timing and loudness of the two tones were simultaneously manipulated by up to 54 ms and 20 MIDI units. The relative perceptual salience of the tones was found to depend on their relative intensity, but not on their asynchrony. Then, in a further experiment, listeners were asked whether the tones were simultaneous, asynchrony was harder to detect when the louder tone began earlier (melody lead). Two possible explanations: either musicians perceive familiar combinations of asynchrony and intensity difference as more synchronous than unfamiliar combinations, or sensitivity to synchrony is reduced in the melody-lead condition by forward masking.

anticipation of an event make it more or less prominent (salient)? Moreover, does this depend on the type of tone? Each experiment consisted of 88 trials: 4 tone types x 2 interval sizes x 11 asynchronies. Tone types were pure, harmonic complex with 16 partials (-6 dB per octave), MIDI-synthesized piano, and recorded from a computer-monitored grand piano. The pair of tones in each trial spanned an interval of an octave or a major seventh. Asynchronies varied from-50 ms to 50 ms, in 10 ms steps. The tone duration ranged from 300 to 400 ms so that the overlap of the two tones were constant at 350 ms. Musically trained and untrained listeners were asked to judge these stimuli on two separate occasions, each with a two-alternative forced choice paradigm. In the Experiment 1, they indicated which tone was more prominent. In Experiment 2, they indicated which sounded earlier. Preliminary analysis of Experiment 1 firstly confirmed the finding and theory of Bregman and Pinker (1978) that as

gait monitoring and the auditory consequences of footsteps

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