This study investigated the effects of hedonic valence and emotional arousal on pupillary responses during picture viewing, using a modern infrared eye-tracking system and well-validated pictures from the International Affective Picture System (IAPS). The primary goals were to reassess the effects of hedonic valence and arousal on pupillary responses and to assess the contribution of sympathetic and parasympathetic activity to these changes. Key findings include: - Pupillary changes were larger when viewing emotionally arousing pictures, regardless of whether they were pleasant or unpleasant. - Pupillary changes covaried with skin conductance changes, suggesting that sympathetic nervous system activity modulates these changes. - The relationship between skin conductance and pupillary changes persisted even after controlling for luminance, indicating that pupil dilation is primarily mediated by sympathetic activity. - Heart rate changes showed a different pattern, with larger deceleration when viewing unpleasant pictures compared to pleasant or neutral pictures. The results support the hypothesis that pupillary responses during affective picture viewing reflect emotional arousal associated with increased sympathetic activity, independent of the hedonic valence of the pictures.This study investigated the effects of hedonic valence and emotional arousal on pupillary responses during picture viewing, using a modern infrared eye-tracking system and well-validated pictures from the International Affective Picture System (IAPS). The primary goals were to reassess the effects of hedonic valence and arousal on pupillary responses and to assess the contribution of sympathetic and parasympathetic activity to these changes. Key findings include: - Pupillary changes were larger when viewing emotionally arousing pictures, regardless of whether they were pleasant or unpleasant. - Pupillary changes covaried with skin conductance changes, suggesting that sympathetic nervous system activity modulates these changes. - The relationship between skin conductance and pupillary changes persisted even after controlling for luminance, indicating that pupil dilation is primarily mediated by sympathetic activity. - Heart rate changes showed a different pattern, with larger deceleration when viewing unpleasant pictures compared to pleasant or neutral pictures. The results support the hypothesis that pupillary responses during affective picture viewing reflect emotional arousal associated with increased sympathetic activity, independent of the hedonic valence of the pictures.