Temporal dependence in perceptual decision-making: behavioural oscillations and sequential effects

Abstract

Dynamic brain states influence perceptual decision making, especially when the immediate sensory evidence is noisy. In this thesis, I examine how perceptual decision making is shaped by two types of temporal contexts, one characterised by intrinsic temporal organisation of neural processing (i.e., neural oscillations) and one characterised by the recent history of perceptual, decisional, and motor experience (i.e., sequential effects). Chapter 2 examines rhythmic fluctuations of behavioural performance in visual orientation discrimination. The results indicate that sensitivity and response bias both modulate rhythmically over time: ~8 Hz for sensitivity, and ~10 Hz for response bias. Chapter 3 examines sequential effects in visual orientation discrimination. Analysing the data-set from chapter 2 shows that it’s the response, rather than the stimulus, that carries over to the next trial. Moreover, the one-trial back sequential effect shows individual differences (positive or negative). In a new experiment with a trial-by-trial random stimulus-response mapping, the choice effect was consistently positive and the motor effect was consistently repulsive, suggesting that the individual differences may be caused by different relative weightings of the perceptual decision and the motor response. Chapter 4 further examines sequential effects with auditory stimuli of different morph levels in two dimensions: gender, syllable (ba/da). Observers reported male or female and ba or da at the same time. For gender, decisions were biased towards the previous choice, and this bias was modulated by the similarity between previous and current stimuli – being stronger when the stimuli were similar. For syllable, the same bias towards previous choice was found, but the dependence was not modulated by similarity between temporally adjacent stimuli. To summarise, these findings reveal that both intrinsic neural oscillations and past history shape the current perceptual decision making.