Since 2015 video dimensionality has expanded to higher spatial and temporal resolutions and a wider colour gamut. This High Dynamic Range (HDR) content has gained traction in the consumer space as it delivers an enhanced quality of experience. At the same time, the complexity of codecs is growing. This has driven the development of tools for content-adaptive optimisation that achieve optimal rate-distortion performance for HDR video at 4K resolution. While improvements of just a few percentage points in BD-Rate (1-5%) are significant for the streaming media industry, the impact on subjective quality has been less studied especially for HDR/AV1. In this paper, we conduct a subjective quality assessment (42 subjects) of 4K HDR content with a per-clip optimisation strategy. We correlate these subjective scores with existing popular objective metrics used in standard development and show that some perceptual metrics correlate surprisingly well even though they are not tuned for HDR. We find that the DSQCS protocol is too insensitive to categorically compare the methods but the data allows us to make recommendations about the use of experts vs non-experts in HDR studies, and explain the subjective impact of film grain in HDR content under compression.

Emotional expressivity is essential for human interactions, informing both perception and decision-making. Here, we examine whether creating an audio-visual emotional channel mismatch influences decision-making in a cooperative task with a virtual character. We created a virtual character that was either congruent in its emotional expression (smiling in the face and voice) or incongruent (smiling in only one channel). People (N = 98) evaluated the character in terms of valence and arousal in an online study; then, visitors in a museum played the “lunar survival task” with the character over three experiments (N = 597, 78, 101, respectively). Exploratory results suggest that multi-modal expressions are perceived, and reacted upon, differently than unimodal expressions, supporting previous theories of audio-visual integration.

Emotional expressivity can boost trust in human-human and human-machine interaction. As a multimodal phenomenon, previous research argued that a mismatch in the expressive channels provides evidence of joint audio-video emotional processing. However, while previous work studied this from the point of view of emotion recognition and processing, not much is known about what effect a multimodal agent would have on a human-agent interaction task. Also, agent appearance could influence this interaction too. Here we manipulated the agent’s multimodal emotional expression (”smiling face” and ”smiling voice”, or both) and agent type (photorealistic or cartoon-like virtual human) and assessed people’s trust toward this agent. We measured trust using a mixed-methods approach, combining behavioural data from a survival task, questionnaire ratings and qualitative comments. These methods gave different results: while people commented on the importance of emotional expressivity in the agent’s voice, this factor had limited influence on trusting behaviours; while people rated the cartoon-like agent on several traits higher than the photorealistic one, the agent’s style also was not the most influential feature on people’s trusting behaviour. These results highlight the contribution of a mixed-methods approach in human-machine interaction, as both explicit and implicit perception and behaviour will contribute to the success of the interaction.