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22 Temporal Perception in the Context of Action Kielan Yarrow and Sukhvinder S. Obhi We do not usually experience the world as passive recipients of sensory information. Instead, we explore our environment through action. For senses like sight and touch, a framework exists to explain how we can interpret and predict the consequences of our own actions. In order to accurately distinguish sensory events arising in the environment from the sensations we ourselves generate, we make use of an efferent copy of our motor command(s) to generate predictions (Sperry, 1950; von Holst & Mittelstaedt, 1950). In this chapter, we will offer a selective review of studies investigating how our sense of time is affected by our own actions. These studies address how we determine the time of an action (section 22.1), and also how both the sensory consequences of action (section 22.2) and externally generated stimuli occurring around the time of actions (section 22.3) are processed by the brain in order to determine a subjective temporal narrative of events. 22.1 The Perceived Moment of an Action 22.1.1 Actions as Complexes of Events Actions unfold over time. For brief motor acts, the physical movement of the body is just the tip of the iceberg. Whereas movements can be reflexive, such as the extension of a knee in response to a physician’s tap, actions comprise both an observable movement component and a series of hidden, mental components. Thus, in action, overt movement is preceded by a sequence of preparatory internal events. These have been inferred from the behavioral assays of cognitive psychologists (e.g., Rosenbaum, 1980; Sternberg et al., 1978) and also observed directly in neural measurements (e.g., for the development of readiness potentials in EEGs, see Kornhuber & Deecke, 1965; for changes in premovement motor cortical excitability indexed by motor-evoked potentials elicited with transcranial magnetic stimulation, see Chen et al., 1998). Indeed, every action generates a complex of internal events, reflecting for example the decision to move; the creation of a motor plan; the transmission of that plan to the muscles of the body; the re-afferent feedback that results from the body’s movement; and the (iterative ) use of this re-afference in correcting the movement. This simple fact implies that any 456 Kielan Yarrow and Sukhvinder S. Obhi experimental attempt to retrieve a subjective report about the time of an action should be scrutinized very carefully. For one thing, the extent to which a subjective report can accurately separate the internal events that collectively define an action is a matter of debate (although this has certainly not prevented researchers from asking questions of this kind). In the rest of section 22.1, we describe some attempts to grapple with these kinds of issues and thus determine the subjective time of actions. 22.1.2 Watching the Clock Although by no means the first attempt to investigate the perceived time of action, a good (and oft-cited) starting point can be found in the classic study of Libet et al. (1983). These authors made use of the “complication” experiment (Dunlap 1910a) in which a visual clock (in Libet et al.’s case, a spot of light rotating around a clock face with a period of 2560 ms) is used to estimate the time of an event. The relevant events that Libet et al. (1983) investigated were the moment at which an action was 1) intended, and 2) physically initiated (as well as the time of an auditory tone, used as a control). The most famous result from this study relates to the time at which participants reported they first intended to act. Naturally enough, this time preceded the moment of action initiation. However, it was itself preceded by the onset of the readiness potential, an event-related potential (ERP) that can be recorded in the EEG in the lead-up to an action. This result led the authors to conclude that the conscious decision to move does not in fact initiate action, but rather follows on from unconscious mental activity that is itself causal in nature. This interpretation has given rise to considerable controversy. We might, for example, question whether the first-deflection method used to estimate the onset of an ERP, which will reflect the left-tail of the distribution of activity across trials, provides a fair comparison with the mean average of clock estimates (Trevena & Miller, 2002). Commentators have also questioned whether equating the readiness potential with the intention to...

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