(Subjective) times they are a changin’: experiments in time processing and illusory duration
While objective time marches, subjective time cadenzas. Objectively, one second lasts one second, however subjectively time can expand and contract depending on what is happening. Which lasts longer, a minute on a roller coaster or one spent doing your taxes? In this thesis I had people perform the psychometric equivalent of riding a roller coaster; doing tedious cognitive science experiments. In doing so, I investigated the role that bottom-up perception, top-down attention, and memory, play in establishing subjective duration. The work contained herein supports the conjectures of the processing principle proposed by Matthews and Meck (2016).
Several manipulations of perceived duration were performed here, as briefly introduced in Chapter 1. In Chapter 2, participants were asked to relax as their motor cortex was stimulated using transcranial magnetic stimulation. Doing this, the excitability of the motor cortex was shown to track duration. The brain is always ‘doing time.’ In Chapter 3, participants were told when an event would occur, information which under normal circumstances would improve performance in a reaction time task. However, this wasn’t the case when participants did not know whether a response would be required. Knowing ‘whether’ trumps knowing ‘when.’
Chapter 4 investigated the role of long-term associations on perceived duration. In particular, it was shown that practicing inhibiting a response to a specific stimulus resulted in a contracted perceived duration of that stimulus in future. This result somewhat challenged the processing principle precepts, and in Chapter 4 we proposed ways to understand the results in a processing principle framework.
Chapters 5 and 6 examined the role of previous temporal experiences on perceived duration. In these chapters, it was found that judgment assimilation occurred; a stimulus was perceived as shorter if the prior stimulus duration was judged as short. This was proposed to be a post-perceptual process of anchoring, such that the prior stimulus provided a starting point for the judgment of the current stimulus duration. Further, this was proposed to be mediated by the difficulty of judging that prior duration.
Chapter 7 investigated whether the magnitude of a current stimulus is affected by the magnitude of the prior stimulus, and whether this sequential contextualisation affects perceived duration. In this chapter, the size of the prior stimulus was shown to affect the perceived duration of a subsequent stimulus, however the numerical value did not. This demonstrated that low-level (visual) information carries over to affect subsequent perceived duration, whilehigh-level (semantic) information may not.
In Chapter 8, participants were required to reproduce the duration of flutter-filled and empty durations while the electrical activity of their brain was recorded. By performing a combination of multivariate pattern analysis and single trial correlational analysis, it was shown that perceived duration in this task was related systematically to frontal activity 300 ms after the onset of auditory flutter. This was proposed to be a marker of ‘surprise’ which then resultedin an expanded perceived duration.
In Chapters 9 and 10, the oddball duration illusion was investigated. In this illusion, a rare or novel stimulus is perceived to last longer than a repeated stimulus. Chapter 9 shows that this illusion is not a product of earlier gating of the stimulus onset. Chapter 10, on the other hand, shows a marked temporal expectation effect which cannot be explained by other theories related to the oddball duration illusion.
While the experiments of this thesis examine various aspects of perceived time from different angles, in the final chapter, how these various manipulations fit into a single overarching framework is discussed. Namely, the processing principle is supported by the findings of this thesis.