Future Directions

Ultimately, converging evidence from multiple behavioral tasks, analysis techniques, and imaging modalities will be required to present a coherent view of how the brain processes time.

In order to achieve that goal, the following questions, among others, will need to be addressed: What are the lower and upper boundaries of the interval timing mechanism, and how does it interact with and "hand off" functions to both millisecond and circadian timing systems (Hinton and Meck, 1997b)? Might FMRI and EEG be combined to study the neural events that underlie timing in the millisecond range? Can magnets with higher field strength be used to test hypotheses about the neural substrates of timing on finer spatial and temporal scales? Will FMRI be able to identify different "internal clocks" for visual and auditory modalities (see Penney, this volume)? How do the multiple brain areas involved in interval timing interact to produce the subjective experience of the fluent passage of time? How reliable is the pattern of brain activation when different timing tasks are used? How does the scalar property arise from the operation of the neural mechanisms for interval timing (see Church, this volume; Gibbon et al., 1984)? Can timing of particular durations be associated with particular brain regions; for example, might there be a topographical representation of durations in different regions of the striatum (Meck et al., 1998)? What are the roles of the various neurotransmitters involved in timing (see Buhusi, this volume; Meck, 1996), and how do they interact to allow normal time perception as a function of developmental changes and normal aging (see Droit-Volet, this volume; Lustig, this volume)? To what extent is attention required to time short intervals (see Fortin, this volume; Pang and McAuley, this volume), and to what degree much may timing occur without conscious awareness? Is interval timing obligatory in healthy organisms when temporal regularities exist in the environment, and can striatal coincidence detection or cortical oscillations account for this phenomenon (see Matell et al., this volume; Meck, 2002)? These and other questions are likely to govern the direction of interval timing research for years to come in our pursuit of understanding how time flies (Hinton and Meck, 1997a).

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