I just read an article on Steven Novella's NeurologicaBlog on temporal binding, a cognitive bias I hadn't seen before:
Temporal binding is a phenomenon that reinforces that assumption of cause and effect once we have linked two events causally in our minds. The effect biases our memory so that we remember the apparent cause and effect occurring closer together in time. In experiments we tend to remember the cause as happening later and the effect happening earlier.
Temporal binding is like the reverse of "post hoc ergo propter hoc", and you could perhaps perhaps also call it "propter hoc ergo post hoc".
Yes, I often notice this same morphing of how people look in my memory. After briefly meeting a new person and then leaving them, I often try to remember their face and find the details slipping through my mental grasp, until I’m imagining someone else, such as a classmate from high school, who I’m more familiar with and who looks a bit like the new person. When this happens, I think to myself, “oh, it’s happened again, I’ve forgotten what they look like already”.