One aspect of thinking affected by dementia is sensory perception. For some people, dementia damages the part of the brain that interprets information that comes from the senses.
For example, your person’s eyesight might be fine (or corrected with glasses) but their brain may have difficulty converting the signals from the eyes into a meaningful picture.
They might experience trouble with depth perception – i.e. judging how deep or far away something is.
They may have trouble picking out an object from its background, particularly if it’s the same colour, there are shadows, or the background is patterned.
Erik used to set out Mary’s clothes for the day on the bed, and Mary would frequently get angry saying “it isn’t helpful when there is no underwear!” Erik would get exasperated and say “it’s there, it is right in front of you”. An occupational therapist pointed out that Mary had difficulty ‘seeing’ white clothes against the white sheet. Placing the clothes on the contrasting bedspread solved this issue.
They may also have difficulty interpreting visual information when there is a mirror, or reflections from wet or shiny surfaces or glare. Cherie found walking on the swirly patterned carpet at the club almost impossible and needed an arm to steady her.
Perceptual changes may also affect the way people with dementia experience hearing, touch, smell and taste.