Recently, Zelaznik
and colleagues (Ivry, Spencer, Zelaznik, & Diedrichsen, 2002; Spencer,
Zelaznik, Diedrichsen,
& Ivry, 2003; Zelaznik, Spencer, & Ivry,
2002) proposed that two
qualitatively different control processes could be used for the timing
of repetitive movements.
When the periodic movements are
marked by salient events, such as during finger tapping, control
processes include a
temporal representation of the target interval
between those events. That form
of control is referred to as event
timing (Ivry et al.). On the other hand, when
the movements
are smooth and continuous, such as during
continuous circle
drawing, the ability to maintain a consistent
rate does not require an explicit
representation of the interval duration. Rather, Zelaznik and colleagues
hypothesized that
timing under such conditions emerges from the
dynamics of trajectory
control. Borrowing from the classic article
of Turvey (1977), they refer to that
form of control as emergent
timing (Spencer et al.).
