On the time scale of human communication, there is empirical support for at least two distinct types of timing mechanisms: an interval-based (‘stopwatch’) mechanism that records, stores and compares event durations and a beat-based (‘entrainment’) mechanism that assesses the relative timing of events with respect to an internally-generated periodicity. A topic of research on timing that has received relatively little research attention is the issue of individual differences. This project considers the possibility that individuals engage in beat-based and interval-based timing, but do so to different degrees. The general aim of the NSF funded project is to identify and characterize factors mediating engagement of beat-based and interval-based timing mechanisms. For this project three inter-related lines of research combine a novel sequence-timing paradigm that demonstrates robust individual differences, with a mathematical model that indexes the degree to which performance reflects beat-based judgments. Critical to the sequence-timing paradigm are stimulus sequences that yield opposite perceptions about sequence rate (‘speeding up’ versus ‘slowing down’) depending on whether individuals engage in beat-based or interval-based timing, respectively. The first line examines stimulus characteristics mediating beat-based timing. The second line assesses flexibility in timing mode, focusing on attention and task factors. The third line addresses developmental and training factors. A key contribution of the modeling work is that it integrates two contrasting theories of timing within a single framework. Using this framework to clarify the degree to which individuals engage in beat-based timing improves current limited understanding of individual differences in timing behavior and helps better characterize temporal processing deficits linked to neurological disorders.