Zombies and corpses fall at the very bottom of the uncanny valley.
What distinguishes these from humans is the fundamental processes that mean we are alive.
Prior work has considered what properties distinguish faces and bodies from being real or fake.
And how to create multi-layer skin models that capture the subsurface scattering of light.
And motions due to respiration.
Blood flow causes subtle changes in light reflected from the skin.
We present a novel approach to animating these dynamic changes on an avatar.
These intensity variations have characteristic spatial distributions, color composition and temporal dynamics.
If we use a baseline using heuristics that govern these changes the appearance is a lot less natural than using a physiologically based model.
Here the animations are exaggerated for illustration purposes.
The spatial component of our model is learnt using a convolutional attention network.
That is trained on videos of human faces.
Specifically, we leverage the attention mechanism.
When the model is trained this can then be given a new video frame and produces an estimate of the perfusion.
The different color channels of a video frame are impacted differently by blood flow.
Using these data from the hemoglobin absorption spectra and empirical evidence of the strength of the pulse signal in each color channel ...
... we create a color space vector for the pulsatile signal.
The blood volume pulse has a characteristic temporal profile, with systolic and diastolic peaks.
We use real PPG recordings to animate these dynamics.
Here are side-by-side examples of the original avatar, animations using the baseline and our physiologically-based model.
The changes are very subtle and we have removed other visual distractions such as head motions.
Here we have exaggerated the changes for illustration purposes.
Here is another example applied to a photograph.
Again the animations have been exaggerated.
We performed an evaluation experiment in which subjects significantly more frequently selected the avatar animated using our approach ...
... as more natural, lifelike and conscious compared to the original.
However, because the appearance changes were subtle many participants could not identify the differences.
This suggests that changes in their perceptions of the avatars may even be unconscious.
Furthermore, manipulating the frequency of the subtle blood flow appearance changes allowed us to create the effect of increased physiological arousal.
Again, participants found it difficult to identify the differences between the avatars explicitly.
But chose the avatars with higher heart rates as more physiologically aroused, more frequently.
While almost imperceptible, adding physiological changes based on blood flow ...
... leads agents to being rated as more natural, lifelike and conscious.
Realistic color space changes are most important.
But dynamics and spatial distribution also help create a more natural appearnce.
Increasing the frequency of blood flow gives the impression of greater physiological arousal.