What explains polarization in authoritarian regimes? I problematize existing literature on repression in authoritarian regimes and radical actor moderation, and incorporate theories and evidence from behavioral psychology to propose an original explanation for the way in which experiences of repression condition levels of polarization. Specifically, I argue that the extent to which repressive experiences are shared by opposition elite determines whether repression fosters ideological polarization or convergence among these political actors through a collective memory formation mechanism. The empirics of the larger dissertation project are drawn from a paired case study of Egypt and Tunisia, two countries which experienced uprisings that unseated long-standing presidents in 2011 as part of a larger wave of mobilization, popularly referred to as the “Arab Spring.” The new political elite charged with governing the country were drawn from the opposition under the old regime. I argue that the explanation for the difference in polarization on the Islamist-secular axis of competition in these countries in 2011 lies in the patterns of regime repression during the previous authoritarian period, particularly under the regimes immediately preceding the uprisings. In this paper, I present the design and results of lab experiments conducted among a student pool at Cairo University in Cairo, Egypt during Spring 2016. The experiments utilize dynamic process tracing to demonstrate the collective memory mechanism through which experiences of repression condition group identification, group-related preferences, and cooperative behaviors. In the paper, I discuss the utility of pairing experiments with in-depth qualitative work; the lab experiments supplement comparative historical analyses of real world actors and provide additional causal leverage on the relationship between repression and polarization that is difficult to fully capture with observational data.