Abstract
Perceptual decision-making requires assessing sensory information collected from the environment, including both objective and subjective information; this involves effort that might vary according to to reward. For example, you may put more effort into the task if the reward is a bag of chocolate, but you may not be willing to spend that much energy on the task that provides a bag of lettuce as a reward, even though the prices of a bag of lettuce and a bag of chocolate are the same. Therefore, as Berridge and Robinson (2003) defined, the reward should be the thing that can elicit pleasure. Existing literature mainly focuses on how the objective value and physical properties of reward influence perceptual decision-making, but the affective effect of reward is typically being neglected. The overarching goal of my PhD research is to investigate how the affective effect of reward modulates the decision-making process. More precisely, the purpose of the present study was to determine whether and how the affective response to task-irrelevant rewards influences perception and decision-making in healthy human adults.
The first step in this research was to examine whether the rewarding stimulus used in the experiment could induce significant affective state changes (Chapter 4, study 1). The next step was to examine the affective effect of task-irrelevant reward on simple motor decision-making (also called perceptual decision-making) by employing passive image viewing and the Go/Nogo task (Chapter 4, study 1). The passive image viewing task was used to induce a positive or negative affective reaction. The Go/Nogo task was used to examine the effect of reward on simple decision-making. In Chapter 5 (Study 2), by altering the way a rewarding stimulus was presented in experimental trials and blocks, whether reward impacts the decision-making process in a state-dependent or stimulus-driven manner was assessed. As a final step, the neural subtractions responsible for the reward's affective effect were examined (Chapter 6, Study 3). The behaviour was measured using the reaction times of button press responses to stimuli and performance accuracy in all three studies. The neural responses were assessed using electroencephalography (EEG; in particular, ERP) in studies 1 and 2 and functional magnetic resonance imaging (fMRI) in Study 3.
Generally, I found that the affective effect of reward modulates perceptual decision-making. In particular, the affective effect of reward mainly acts on the sensory stimulus processing involved in decision-making, as reflected in amplitude changes of stimulus integration related ERP component and enhanced activation in the primary visual cortex and brain regions involved in the attention system found in Studies 1 and 3. In addition, the affective component of reward facilitated the sensory stimulus processing in a manner akin to top-down control, as Study 2 showed that transient experiencing of pleasure no longer had an impact on decision-making. These findings indicated that the affective effect of reward is a state-dependent effect. That is, the effect needs to accumulate to a certain level. The Hedonic Interface Theory and Unconscious Goal Pursuit Theory account for the findings from a theoretical perspective. To sum up, the present findings suggest that not only the motivational component of reward can directly influence decision-making, but the affective component of the reward itself also plays an essential role in regulating decision-making behaviour. The present findings not only have theoretical implications by highlighting the difference between the emotion system, motivational effect of reward, and affective effect of reward, but they also have practical implications for understanding a range of factors associated with human decision-making behaviour.