The distinction between temporal order and duration processing, and implications for schizophrenia

The term ‘timing’ is interchangeably used to convey processing of the order or the duration of events. Yet, whereas temporal order processing means judging when one event happens relative to another (first or second), duration estimation means measuring how long the event lasts. In this Review, we show that the functional distinction between these two temporal features is reflected in their discrete neural substrates. Temporal order processing preferentially engages the left inferior parietal cortex, whereas duration estimation recruits the supplementary motor area, basal ganglia and cerebellum. The functional distinction between temporal order processing and duration estimation also enables better characterization of temporal perturbations present in clinical disorders. For instance, individuals with schizophrenia have trouble individuating and ordering consecutive events in time and show atypical responses to stimuli that do not appear when expected. Therefore, individuals with schizophrenia might have a fundamental impairment in processing when a stimulus occurs relative to another event, rather than in estimating how long it lasts. These neural and clinical dissociations demonstrate that the phenomenological sensation of a unitary and cohesive flow of time (‘time’s arrow’) can be separated into two distinct, though intertwined, components.