Results
Emotion Ratings. The video set was assembled to evoke both pleasant and unpleasant emotion states across a range of intensities. Consequently, a repeated measures ANOVA found a strong difference between SAM valence ratings between the 5 video categories (F ( 4,164) = 135.60, p< .001;ηG2 = .690). As shown in Figure 1, the pleasant videos elicited the largest valence ratings, followed by highly arousing pleasant, neutral, unpleasant, and highly arousing unpleasant videos, with all differences significant. This pattern of valence ratings is quite consistent with ratings of comparable categories of scenes (Farkas & Sabatinelli, 2023; Frank & Sabatinelli, 2019). Emotional arousal was also strongly modulated by video content (F ( 4,164) = 46.64, p < .001;ηG2 = .285). Arousal ratings were equivalently enhanced by highly arousing pleasant, highly arousing unpleasant, and unpleasant videos. These were followed by arousal ratings for pleasant videos, while neutral videos were rated as least arousing. Table 1 lists the emotion rating means for each video, in addition to luminance, sound intensity, entropy, entropy standard deviation, and pixel motion.
Steady-State visual evoked potential. Steady state visual evoked potential amplitude did not differ between the first and second presentation of the videos (see Table 2) and were averaged together. Shown in Figure 2, raw steady-state evoked amplitude was maximal over occipital regions and significantly modulated by video content from 1-9 seconds after video onset (F ( 4,164) = 14.21, p< .001; ηG2 = .013), with decreases in 7.5 Hz power evident during emotional, compared to neutral videos. Standardizing ssVEP amplitude across participants yielded the same pattern of modulation, with considerably greater effect size (F ( 4,164) = 16.17, p < .001;ηG2 = .283). Shown in Figure 3, video categories sharing the same letter in the legend (a, b, or c) do not significantly differ. Thus, highly arousing unpleasant, unpleasant, and highly arousing pleasant videos reduced ssVEP amplitude equivalently, followed by ssVEP amplitude during pleasant videos, which differed only from ssVEP amplitude during high unpleasant and unpleasant videos. Lastly, neutral videos evoked the smallest reduction in ssVEP amplitude, different from ssVEP amplitude during all other video categories but pleasant, which was marginal (t = 2.72, p = .056). Also shown in Figure 3 is a histogram of individual participants’ ssVEP amplitude across the 5 categories, representing the consistency of ssVEP modulation across video content across the sample.
Pearson’s correlations were used to assess the relationship between raw ssVEP amplitude and emotional and perceptual video features. Thus the averaged ssVEP amplitude for the subset of participants with data for each of the 45 videos (average 34.2, SD = 4.6) was compared with the emotional ratings and quantitative measures from all 42 participants. This analysis could reveal relationships between ssVEP amplitude and video features that may be confounded with 5 video categories. For example, if videos with high luminance, sound intensity, or motion tended to reduce ssVEP amplitude, and occurred more often in emotional videos, correlations of these values may emerge if these features were not sufficiently distributed across the 5 categories. Shown in Table 3, ssVEP amplitude correlated only with arousal ratings (R2 = .308, p < .001), while valence ratings and all perceptual features showed no significant association. A trend suggests a relationship between entropy SD (variability in perceptual complexity over time) across the video and ssVEP amplitude (R2 = .074, p = .07). Shown in Figure 4, when averaged by video category across the sample of 42, the correlation of arousal ratings and ssVEP amplitude was very high (R2 = .97, p < .01).