Shadow-Induced Forgetting in a Game-Based Paradigm on Nonclinical Adults and Its Effects on Consciousness, Emotional Valence, and Temporal Dynamics: Crossover Study.

Background: Memory suppression transiently disrupts hippocampal activity, leading to suppression-induced forgetting, especially for negative stimuli. However, traditional paradigms such as Think/No-Think rely on explicit control and lack ecological validity. This study introduces a game-based task that implicitly elicits suppression through reversed motor mappings, providing a naturalistic approach to studying memory inhibition. Objective: This study aims to examine how shadow-induced forgetting (ShIF) varies across short-term and long-term intervals (0 hours, 24 hours, and 72 hours), under conscious versus unconscious exposure, and between positive and negative emotional stimuli. Methods: This single-center, within-subjects experimental study involved 56 university students (mean age 23.37, SD 1.84 years) and was conducted between December 1, 2023, and March 1, 2024. Participants learned 36 cue-target image pairs varying in emotional valence (positive and negative). They underwent a game-based paradigm where habitual motor responses were disrupted through reversed key mappings to induce an amnesic shadow. During gameplay, selected cues were presented either consciously or unconsciously, while others served as controls. Memory performance was assessed using Metric for Evaluation of Translation with Explicit Ordering scores (semantic similarity) immediately after intervention (0 hour) and again at 24 hours and 72 hours. Electroencephalography was recorded in a subset of 40 participants to examine neural correlates of memory suppression. Results: ShIF effects were short-term, conscious-dependent, and selective for negative memories. A significant interaction between exposure condition and time (F₃.₆₂,₁₉₉.₃₃=2.7, P=.04, η²p=0.05, 95% CI 0.00-1.00) indicated that the effect varied across time points. Specifically, a significant ShIF effect emerged immediately after the intervention (0 hour) in the conscious condition (t₅₅=-2.86, P=.02, d=0.38) but was absent in the unconscious condition and dissipated by 72 hours. Robust main effects of time (F₂,₁₀₉.₉₉=102.91, P<.001, η²p=0.65, 95% CI 0.57-1.00) and emotional valence (F₁,₅₅=42.43, P<.001, η²p=0.44, 95% CI 0.27-1.00) showed that overall recall declined over time and was consistently lower for negative images. Electroencephalography analyses revealed enhanced right frontal beta (FC6, F4, and F8: P<.001) and posterior gamma (O1: P<.001, O2: P<.001, and P8: P=.002) activity during suppression of negative cues, reflecting neural inhibition processes underlying ShIF. Conclusions: ShIF occurs primarily for consciously processed negative memories and diminishes over several days, highlighting the temporal and emotional boundaries of intentional forgetting. This study introduces a game-based approach that extends traditional suppression paradigms and offers an ecologically valid framework for investigating memory control. Importantly, we demonstrate that suppression can be induced through a game-based paradigm. By examining emotional valence, exposure condition, and temporal dynamics, we extend previous work focused only on transient effects and clarify the potential for practical implementation in digital therapeutic applications such as posttraumatic stress disorder treatment.