New Challenges

Showing that controlled attention may be implicated in temporal parameters and have determinant effects on timing performance was an exciting challenge 20 years ago. Now that this challenge has been won, another, complementary one is forthcoming, namely, the outcome of prolonged learning, which leads to automatic performance. Data obtained in timing (Casini et al., 1999; see Pouthas, this volume)

as well as in other tasks suggest that efficient processing may be related to low rather than high levels of cortical activity. Whether this reflects transfer toward subcortical pathways or concentration on narrower, very specific neural foci is an open question. Training in most experimental tasks is generally rather brief. How does cortical activation evolve after extended training, and above all, how do temporal representations evolve? Data on motor control show that bimanual transfer is obtained in early learning phases, but not after long-term practice limited to one hand (Hikosaka et al., 1999). Can we expect analogous effects on timing, suggesting that a novel temporal representation is first available to different effectors and sensory modalities, but becomes specific to the behavioral context and to the motor program it created once performance is automatized?

The role of context itself is another urgent question, possibly underestimated so far. Context seems to have a marked influence on timing (e.g., the effects of gaps and modality — see Buhusi, this volume; Penney, this volume), as on many other types of processing. A meta-analysis considering contextual parameters may enlighten interpretation of various data sets, in the same manner as attentional findings have stimulated new insights into various theoretical frameworks, and may continue doing so if they are systematically taken into account in forthcoming research (for new questions raised by the dopaminergic involvement in attention sharing, see Buhusi, this volume). An interesting approach would also be to consider how context might have determined the level of attention paid to relevant vs. irrelevant parameters in a number of tasks.

With respect to brain structures, a current issue that is likely to be clarified in the near future is whether the striato-frontal and the cerebello-frontal circuits have complementary functions in timing tasks. A related question lies in the sequential activation of the anatomical pathways involved in timing, not only between the distinct functional modules of timing models, but even within each module itself. Attempts to describe activation sequences during information processing are still rather timid, but might soon be successful, thanks to a combination of brain imaging techniques and their continuous improvement (e.g., the increasingly fine temporal resolution of functional magnetic resonance imaging (fMRI) and its co-registration with electroencephalography (EEG)) (see Hinton, this volume; Sakata and Onoda, this volume). Finally, separating the components of the timer, and relating each one to dedicated brain structures, is currently a hot topic, though by no means easy to solve (see Lewis and Miall, this volume; Rao et al., 2001) or even mandatory (see Matell et al., this volume). This raises particularly delicate problems when considering that certain components may unfold simultaneously (as for comparison and encoding during a test interval) or may have a very brief time course (as for decision).

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