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We report here a preliminary study of interactive behavior between two members of a skilled string quartet performing a selected musical passage that required both performers to play several hundred notes in rapid succession at a steady tempo and in synchrony. Bowing movements were recorded using angular velocity sensors attached to their right forearms. The results show a high degree of temporal precision in both players. In addition, both players exhibited embedded rhythmic components in their timekeeping pattern, which arose from the grouping of notes in the musical score: four 16th notes to a beat. Within each group of four notes, we found a consistent timing microstructure: alternate upbows and alternate downbows had different mean durations. Both players' bowings could be modeled as alternating renewal processes. In addition, we report evidence of interactive coupling between the players as an essential component of their joint performance. The alternating renewal model enables us to propose a note-generation process that has implications for the central generators underlying the observed behavior and their hierarchical organization. We discuss the implications of this model for the organization and execution of more complex motor sequences.

Based on a newly developed method that combines finger position tracking and spectral analysis of the concurrent acoustic record, we studied the accuracy and variability of pitch performance in eight skilled cellists and the role of acoustic feedback in their performance. The tasks required shifting movements between pairs of notes and separated by various distances (pitch intervals) on a single string at the rate of 1 note/s. The same tasks were performed either using the bow, providing acoustic feedback, or without the bow. Overall, our subjects exhibited a high degree of accuracy in executing tasks when using the bow. When using the bow, two types of variability were observed: (1) trial-to-trial variability: in most subjects the mean fundamental frequency of a single nominal note was significantly different from trial to trial; and (2) within-trial variability. The within-trial variability includes two sub-types: (a) the pitch of a given note changed between notes within a 50-note trial; and (b) within a single note there were positional changes that we hypothesize are attempts by the performer to adjust the fundamental pitch within the note. When acoustic feedback was absent, note distributions were shifted, multimodal, and had large variability; error-correction movements within a single note also significantly decreased, indicating that the stability and precision of the motor map depends on constant re-calibration and updating by acoustic information. Our results suggest that a performer's intonation should not be viewed as a fixed entity implied by the score but as a sample from a statistical distribution.

The development of a procedure to culture wool follicles from Merino sheep in serum-free conditions has enabled us to investigate the actions of epidermal growth factor (EGF) and transforming growth factor alpha (TGF alpha) on follicle function, including fibre growth. Follicles grown in the absence of growth factors maintained their anagen morphology for 6 days as determined by light microscopy. During this time they incorporated [3H]thymidine into the DNA of the bulb matrix and outer root sheath (ORS) cells and produced fibre keratins as detected by immunohistochemistry. In the presence of EGF and TGF alpha, fibre production ceased after 4 days, as it does following the administration of EGF in vivo. Cessation of fibre growth was not accompanied by regression of the follicle bulb which occurs in vivo. Follicle length growth did not differ significantly from controls and cells in the bulb continued to proliferate. Usually, the structure of the dermal papillae resembled that in control follicles, which was also in marked contrast to changes reported in vivo. In EGF- and TGF alpha-treated follicles, [3H]thymidine continued to be incorporated into DNA of the ORS and bulb after fibre growth ceased. Although wool keratin synthesis ceased, cytokeratins of the epidermis and ORS continued to be produced in the bulb as detected by immunochemistry. These bulb cells were also positive for the periodic acid-Schiff (PAS) reaction indicating the presence of glycogen, a normal component of ORS cells. The observations that cell proliferation continued in the bulb, that glycogen was present and that soft keratins were expressed in these cells suggest that the bulb cell population was induced to differentiate into an ORS phenotype by EGF and TGF alpha.

Mesenchymal components of skin and vibrissa follicles of the sheep have been introduced into culture. Outgrowths of cells were obtained from explants of the dermal papilla, follicular capsule, dermal sheath and the reticular region of the dermis. Following trypsinization, the cells were successfully propagated as monolayers through several passages. As numbers increased, both the papilla and sheath cells displayed aggregative behaviour. Capsular and dermal fibroblasts did not aggregate but became aligned into polarized arrays, the cells appearing to exert tractional forces on each other and the surface of the culture dish. In general, cell proliferation was promoted by fetal bovine serum (FBS), epidermal growth factor (EGF) and fibroblast growth factor (FGF), although the extents of the responses varied amongst the different types. Dermal fibroblasts underwent the greatest increase in numbers in the presence of FBS. The sheath and papilla cells, by contrast, were more responsive to EGF than dermal fibroblasts, with capsular fibroblasts displaying an intermediate response. Intense EGF immunoreactivity was detected in Western immunoblots of freshly isolated capsular tissue. The presence of EGF-like activity in capsular extracts was confirmed by radioreceptor assay, suggesting a specific autocrine or paracrine function for the growth factor in the local follicular environment. Mitogenic responses to FGF were approximately equivalent in all cell types when compared with controls. The similarities in aggregative behaviour and proliferative responses displayed by the dermal sheath and papilla cells suggest that they may be members of a lineage which diverged from that giving rise to the other mesenchymal derivatives during early follicle development.

Procedures to promote the growth of primary cultures of keratinocytes derived from sheep epidermis through several passages are described. Rapid epithelial outgrowth was obtained from explants of epidermis isolated from trypsinized inguinal skin biopsy specimens. Following initiation and attachment, cells displayed the polygonal morphology typical of keratinocytes in culture and survived a number of passages before terminally differentiating and sloughing from the surface of the culture vessel. Proliferation occurred in the absence of a feeder layer and was attained in a medium supplemented with foetal bovine serum and hydrocortisone or cholera toxin. Growth was stimulated by the addition of epidermal growth factor or fibroblast growth factor (FGF) to the culture medium. The detection of basic-FGF immunoreactivity in Western immunoblots of extracts of fresh tissues suggests a role for this factor in autocrine or paracrine growth regulation of skin cell populations in vivo.

Temporal information processing was studied in humans attempting to tap a key in synchrony with a metronome whose base period was subjected to subliminal random changes. Statistical measures of the sequential timing of metronome and key-tap events were compared with similar time series generated by computer-simulated models of synchronization strategies. From this analysis, synchronization appears to be a sensory-dependent second-order recursive process indexed and stabilized by a combination of internal and external resetting events, with at least two independent sources of timing error.

Timing measures were obtained from subjects instructed to tap a Morse key in synchrony with a metronome which marked a timing pattern consisting of alternating blocks of intervals of imperceptibly different duration. "Synchronization strategies", which consisted of computer-simulated sets of rules, or algorithms, hypothesized to be the basis of synchronization behavior, were used to simulate tapping sequences in response to the same metronome sequences. The human and computer-simulated synchronization data were analyzed identically and compared to determine which of the postulated strategies could explain the observed human tapping behavior. The strategies generating timing data statistically indistinguishable from the human data involve a pattern of human-metronome interaction, and a corresponding transfer of information, more complex and subtle than previous investigations had implied.