Dedicated and intrinsic models of time perception

Abstract

Two general frameworks have been articulated to describe how the passage of time is perceived. One emphasizes that the judgment of the duration of a stimulus depends on the operation of dedicated neural mechanisms specialized for representing the temporal relationships between events. Alternatively, the representation of duration could be ubiquitous, arising from the intrinsic dynamics of nondedicated neural mechanisms. In such models, duration might be encoded directly through the amount of activation of sensory processes or as spatial patterns of activity in a network of neurons. Although intrinsic models are neurally plausible, we highlight several issues that must be addressed before we dispense with models of duration perception that are based on dedicated processes.

Figure 1

Neural models for temporal representation. The top two panels depict two dedicated models. (a) A neural structure might be specialized to represent temporal information. The example shows the cerebellum as a dedicated system, although some models postulate a specialized role for the basal ganglia, supplementary motor area or right prefrontal cortex. (b) A dedicated system could involve activity across a distributed network of neural regions. The bottom two panels depict two models for modality-specific intrinsic timing. (c) In a state-dependent network, temporal patterns are represented as spatial patterns of activity across a neural network. (d) In an energy readout model, elapsed time corresponds to the amount of neural activity.

Figure 2

Nontemporal processes influence on the passage of time. (a) Decision processes in a time-perception task can be biased by nontemporal factors. For a stimulus presented for a fixed duration, a visual display composed of many dots is perceived as longer than a display composed of few dots. This illusion could result from the incidental activation of the overlap of spatial and temporal concepts. The spatial concepts ‘few’ and ‘many’ map onto ‘short’ and ‘long’, respectively. (b) Processes involved in detecting the onset and offset of a stimulus will influence perceived time. The registration threshold for an attended object is lower than for an unattended object. Assuming attention is then directed to the stimulus, the threshold for registering the offset will be the same for both stimuli, resulting in a longer perceived duration for the attended object. Similarly, faster detection times for the onset of an auditory stimulus might help explain why auditory stimuli are perceived as longer than visual stimuli. These nontemporal effects are relevant independent of whether temporal processing is dependent on dedicated or intrinsic mechanisms.