We studied the effect of emotion generated by IAPS (International Affective Picture System) pictures on incidental recognition of these pictures for short retention periods (15 min). Memorization distraction tasks and reaction time tasks were used together with short exposure times (2 seconds per picture) in order to prevent a high recognition rate that would impede testing for the effect of emotion on discrimination parameters (A´) and response bias (B´´D) (ceiling effect). We used 80 pictures representing the medium and high levels of two-dimensional emotional space. The results showed greater discrimination and a more conservative response style to unpleasant and medium arousal level pictures. These pictures produced higher confidence and lower response times in the recognition phase. The results can be explained by the negative content of the pictures and activation level effects on attentional processing and memory, and can be interpreted as a phenomenon that is evolutionarily adaptive.