Fig. 2

Experimental design. (A) Example sequence for Experiment 1 using affective sounds. Participants viewed 10 different luminances presented pseudorandomly for 63 s each. While viewing the luminances, participants simultaneously listened to auditory stimuli of Negative and Neutral valence, while rating their subjective arousal for each sound on the keyboard on a scale from 1 to 5. (B) Example sequence for Experiment 2A & 2B using affective pictures. Every trial consisted of three parts: (1) A baseline luminance adaptation period was presented for 10 s to allow the pupil to adjust to the current luminance; (2) After the adaptation period, the image was presented at fixation for 6 s while the background luminance was held constant from the adaptation period; (3) Following the image presentation, the image and the luminance were cleared from the screen, which indicated the start of the 2 s response period. The 10 different luminances were presented in pseudorandom order. While viewing the luminances, participants simultaneously viewed images of Negative and Neutral valence presented centrally and entered their subjective arousal rating for each image on the keyboard on a scale from 1 to 5. In Experiment 2A, the images were presented in grayscale, luminance and spatial frequency-matched. In Experiment 2B, in which the images were presented in color, luminance-matched.