The effect of positive and negative mood on different cognitive processes remains largely unknown due to mixed findings. One reason for this is that the methods used in mood induction procedures are widely varied. This study therefore aimed to elucidate the effect of positive and negative mood on two cognitive processes used extensively in daily life: working memory capacity measured using the running memory span, and prepotent inhibition measured using the Flanker task. This study also utilized the three parameters (mu, sigma and tau) of ex-Gaussian distribution to analyze the reaction time data. Participants (N = 306) were predominantly young adults recruited from an undergraduate sample (M = 21.1 years old, SD = 4.2). They were randomly assigned to a positive, negative, or neutral mood group and underwent a mood induction by a watching 3-minute-long video clip. They then performed the running memory span or the Flanker task in a counter-balanced order. Analysis of variance indicate that there was no effect of condition on working memory capacity nor prepotent inhibition. Exploratory analyses indicated that positive mood showed a non-significant tendency to be associated with greater difficulty in prepotent response inhibition, whereas negative mood showed a non-significant tendency to be associated with slower responses (larger tau) in stimulus incompatible trials. These mixed findings suggest that positive and negative mood might influence response inhibition differentially and that there needs to be further experimentation to clarify the differential effect of positive and negative mood on different cognitive processes.

When an organism experiences a salient event, such as when a reward or punishment is received, it is crucial that the information pertaining to that stimulus is encoded and consolidated into memory. The memory of the salient event then allows the organism to continue seeking or avoiding that stimulus. However, it is essential that the organism is also able to recognize the events leading up to encountering the salient stimuli. Theoretically, this requires retroactive enhancement of memory. Retroactive enhancement of memory occurs when previously seemingly irrelevant memories are enhanced at a later time point due to a salient event. While there is theoretical support for the possibility of retroactive enhancement of memories, the empirical evidence in human participants has largely been mixed primarily due to methodological differences and conflation of learning paradigms. Furthermore, as prior studies that have attempted to elicit retroactive enhancement of memory using rewards have only used monetary rewards, it is unclear if social rewards could elicit the effect as well. The effect of retroactive enhancement of memory using rewards on false memories is also unclear. To address the inconsistencies and ambiguities in the literature, this dissertation examined the effects of monetary and social rewards on retroactive enhancement of memory and false memories using an operant conditioning paradigm in Study 1 and a classical conditioning paradigm in Study 2. First, while the data in Study 1 provided evidence of retroactive enhancement of memory for both monetary and social rewards, the data in Study 2 did not support retroactive enhancement of memory. Second, using a two-step conditioning process, results from Study 1 suggest that monetary and social rewards can exert comparable influence on memory in an operant conditioning paradigm. However, results from Study 2 demonstrated that recall in the conditioning phase of the social reward condition was significantly higher than that of the monetary reward condition using a classical conditioning paradigm. Third, in examining rates of false alarms, the data revealed no significant differences between the reward category images in Study 1. The findings of this dissertation not only add to the extant literature but also provide clarity regarding mixed findings in previous studies. Across these two studies, this dissertation provides important insights regarding one facet of memory, retroactive enhancement of memory, especially in the presence of rewards.