<p>Speech perception shows substantial individual differences, but the mechanisms underlying this variability during real-time accent adaptation in natural conversation remain poorly understood. We used pupillometry to examine the temporal dynamics of processing effort while German listeners followed a semi-natural dialogue alternating between Standard German and an Alemannic regional variety of German. Growth curve analysis of the within-trial time course revealed switching costs and initial asymmetries, with greater effort for the regional variety and for switches from standard to regional accent. An analysis across the course of the dialogue further showed that the effect of accent driving these asymmetries diminished as listeners adapted to the regional variety. In contrast, switching costs remained stable across the dialogue, consistent with sustained attentional demands. Individual differences modulated these effects. A k-means cluster analysis yielded two clusters of listeners. The group characterized by greater exposure to Standard German, younger age, lower openness, and more favorable comprehensibility and pleasantness ratings for the standard speaker showed higher switching asymmetry, while overall switching costs did not differ reliably between profiles. These results are consistent with the interpretation that switching cost and switching asymmetry may reflect partly distinct underlying processes and that individual differences in language experience and personality selectively shape asymmetries during adaptation to within-first-language accent variation in real-time conversation.</p>