Motivation and emotion effects on cognition are well-studied, but their neural interactions are less understood. In three EEG experiments (N = 32 each), we investigated this under different cognitive task demands, focusing on intrinsic motivation (i.e., self-determined choice) and emotional picture processing. In Experiment 1, a time production task, participants estimated two-second intervals while viewing emotional pictures (neutral, negative, positive), with picture categories (e.g., humans, vehicles, animals) either self-chosen or assigned pseudorandomly (‘self’ vs. ‘no choice’). Enhanced pre-stimulus contingent negative variation (CNV) amplitudes were observed for ‘self’ trials. Late positive potential (LPP) amplitudes were enhanced for self-chosen pictures and highest for negative compared to neutral and positive pictures. However, no motivation-emotion interaction was found, suggesting independent effects on attentional resource allocation. Experiment 2 involved a less demanding active viewing task. No CNV effect related to self-determined choice was present. As in Experiment 1, self-determination and emotional content modulated LPP amplitudes, but again, no interaction was found. Comparing both experiments, this experiment revealed overall higher LPP effects, indicating dependence on cognitive task demands. Experiment 3 excluded the ‘self’ condition, confirming that emotional LPP effects remained unaffected when motivational context was eliminated. These findings suggest that self-determined choice enhances task preparation depending on task context, and that attention during task processing is modulated by self-determination and emotional content similarly across task contexts, albeit elevated in low-load tasks. Results align with models on resource competition in attention allocation but suggest distinct processes for motivation induced by self-determined choice and emotion processing.