Sometimes memory loss isn't a symptom of dementia until it is very advanced. The type of dementia Terry Pratchett had, for example, affected how his brain interpreted vision from his eyes.
"So actually he didn't have memory loss until the late stages, but he couldn't really see at all," Phipps said. "So he couldn't type, and had big gaps in his vision where he couldn't see things."
Alzheimer's Research UK has a virtual reality dementia experience online called A Walk Through Dementia, which shows some of the visual perception tricks dementia can have on someone.
"One thing people often tell us about is that puddles on the ground can look like holes because there are issues with perception and depth perception and colour perception," said Phipps. "You know when you go into a shop and they used to have those big black mats in front of the door... for some people with dementia that looks like a massive abyss."
Imagine being faced with large holes in the ground. It would be confusing and alarming. Phipps said this means people with dementia won't go into shops, or they won't enter bathrooms because the shiny floors look like water.
"If your brain was working 100% you would probably be able to perceive the difference between shiny and wet," she said. "But if there's damage in your brain you just can't quite make the judgement. Those things seem small but they can have a huge impact."