Previous investigations using pictures to elicit an emotional response have shown that the startle reflex habituates over time due to decreased excitation in the obligatory startle processing pathway, an effect that is independent of emotion modulation aspects of the startle response. However, in some instances, startle magnitude has been selectively potentiated during sustained exposure to passively viewed unpleasant pictures. This study assessed startle modulation during brief, alternating and sustained exposure to emotional pictures. Self-reported ratings of emotion were collected online with picture viewing to determine if any change in startle magnitude was observable in explicit emotional responses. Self-reported ratings of pleasantness and arousal were no different across the brief and sustained picture presentations. However, a significant main effect (independent from emotion category) of presentation condition was found for startle magnitudes, showing that, contrary to previous research involving passive picture viewing, mean startle magnitudes during sustained exposure were reduced relative to brief exposure. These findings are likely the result of a general habituation of the startle reflex in the obligatory pathway. The findings are also discussed in terms of the effect of the concurrent emotion rating task, which may have differently affected the cumulative effects of emotion exposure compared to passive picture viewing.