The importance of changes of light and dark in their room to regulate circadian rhythms is supported by mounting research. I doubt that people functioning within ACL 1.0 are awake long enough to notice. Within ACL 1.2 they might. Lights off at night whenever possible will probably become a universal policy.
For babies, the best visual cue is the human face bobbing up and down. Newborn babies do not recognize anyone so a simple smiley face is just as good as Mom and Dad. People with a cognitive disability have memories of loved ones and their access to those memories is observable in heightened responses to the real person and their pictures. Pictures of loved ones capture attention best when the faces are large (6-12 inches or 15-30 cm).
Real people can use a raised eyebrow flash while they bob their head and talk funny. All this talking, bobbing and flashing can make us all feel silly. When the effort captures their attention and they smile, the connection with the person who is still here is wonderful.
All visual cues must be located within tunnel vision, which is about 14 inches (35 cm) in front of their face. Tunnel vision must be considered first because sixty degrees of head turning is often absent or sporadic.
Black and white, primary colors and neon colors attract attention.
Do not limit pictures to loved ones. The lay-out for pictures that will capture their attention is tricky because a single object without a background is needed. Books published for toddlers to teach nouns can be effective if there is one object per page, but multiple objects on a page or cartoons are apt to be ignored. Beautiful landscapes suffer the same fate in ACL 1 and 2. The reason is too much information. Simple and realistic pictures in the colors given above capture their attention when placed in tunnel vision.
Flashing lights can attract attention if you can adjust the flashes to match their response times and turn them off in a minute or two. If other caregivers leave them on too long, they can become a source of irritation and restlessness, heading toward a combative reaction. If so, remove them.
Please note that within ACL 1, visual acuity is fuzzy for everyone. A history of using reading glasses is irrelevant because with or without them, visual attention is restricted to the specifications described above.
Watching bubbles float in the air (ACL 1.2) precedes tracking the bubbles (ACL 1.4).