Two in five people wrongly believe dementia sufferers do not benefit from seeing loved ones they no longer recognise, a charity has warned.
Research carried out by the Alzheimer's Society also found 64% of people with dementia felt isolated from friends and family following diagnosis.
The charity said the findings showed a need for people to spend more time with relatives with the condition in order to prevent loneliness.
It said a poll of members of the public revealed 42% "mistakenly" felt that once a loved one could no longer recognise them then "they don't benefit a lot from spending time with them".
Two in five (41%) also said being unable to recognise friends and family would make them feel most isolated, ahead of a relationship breakdown or divorce at 19%.
Some 68% responded they would still keep up visits, but the charity said: "Despite these good intentions, the lack of awareness of how important emotional memory is may mean that in their busy lives, people don't always follow up on their intentions and over half of those living with dementia are left feeling isolated."
Sufferers still had an "emotional memory", it added, saying visits could "stimulate feelings of familiarity, happiness, comfort and security".
In a separate survey of 300 people with dementia, 54% said they were rarely or no longer taking part in social activity and 51% said having someone to help them get involved would make them less lonely.
Alzheimer's Society chief executive Jeremy Hughes said: "After spending time with friends and family over the festive period, New Year can be a bleak and lonely time for people with dementia and their carers. It's so important for people with dementia to feel connected throughout the year.
"Spending time with loved ones and taking part in meaningful activities can have a powerful and positive impact, even if they don't remember the event itself. We're urging people to get in touch with us and find out how we can help you stay connected."