## 4 Discussion
### RQ3: How Should Psychometrics Assess Emotional Experience? The complexity of emotional processes is the main difficulty in developing an accurate and precise emotion measurement system [74]. Nonetheless, many methods have been developed and validated. Throughout the review, two major tendencies were found: a small group used the discrete dimension of emotions (happiness, sadness), while the main method was the evaluation of valence and arousal. The SAM scale was the most common evaluation observed for emotion measurement. It consists of visual cues to identify perceived levels of valence, arousal, and/or dominance. This visual representation may reduce introspection and cognitive processing compared to other measuring systems (e.g., VAS scale) [75]. In the conducted research, no study compared different psychometric tests for the evaluation of emotions. Nevertheless, SAM has been validated in diverse ethnic groups [76], generally making it the best option for a diversity of subjects. Sample characterizations include psychological health assessments. Mainly anxiety and depression levels were evaluated as an exclusion or inclusion criterion in several studies. These disorders reflect irregularities in the perception of positive and negative emotional stimuli [77]. Hence, in any study regarding emotional responses, the evaluation of anxiety and depression traits should be applied, as the neural correlates directly depend on the mental state of participants. RQ4: Under Which Conditions May Emotion Processing Be Assessed, and How Does the Experimental Paradigm Cause Biases in Emotional Perception? A trend of heterogeneity regarding the procedures for inducing emotions has been highlighted, thus complicating the inter-studies analysis. Previous studies emphasized the modulation of electrophysiological and behavioral mechanisms associated with emotional stimuli presentation and processing modalities [78; 79]. As a case in point, [79] observed better accuracies in face emotion recognition when stimuli were presented for 50 to 100 ms rather than 16.67 ms, and [80] showed that longer duration of emotional auditory stimuli predicted higher and later peak pupil dilation. Most studies designed experimental paradigms so that a fixed time window was used to analyze physiological responses to emotional elicitation. However, [26] outlined better classification of emotions when considering specific short EEG segments (e.g., the 34 last seconds of 1-min emotional music videos). Furthermore, emotional activation processes varied with the valence (i.e., positive, or negative) and intensity of emotions. The dynamic structure of the emotional experience emphasizes two key components: an onset phase correlated with explosiveness and an offset phase associated with accumulation [81]. The explosiveness phase refers to reactivity and is an index of whether the intensity of the emotional perception has a steep versus gentle start. On the other hand, accumulation refers to whether the emotion intensity increases over time or returns to baseline [81]. Explosiveness and accumulation phases showed distinct neural correlates. The former was associated with regions that take part of the default mode network (such as the medial prefrontal cortex), whereas accumulation showed activity in regions involved in visceral sustained arousal (such as the insula) [82]. Distinct neuronal activities emphasize the essential need to consider temporal dynamics when exploring the electrophysiological basis of emotional processing. Consequently, in the future, experimental paradigms should be designed so that temporal phases of emotional processing can be analyzed appropriately. Additionally, the conscious/unconscious nature of the emotional stimulus, which can be correlated to the explicit/implicit way of processing emotion, is another relevant factor that has previously shown to predict electrophysiological correlates [83; 84]. Contrary to explicit processing, implicit processing is defined by the automatic and out-of-conscious focus on emotional information.