You are right Nikki. The key is that what you see and hear must go together logically.
Dr. Robert Titzer talks about the 5 conditions that make a DVD helpful for babies:
5 conditions that make baby or toddler DVDs helpful
1) The DVD should be interactive, not passive.
2) The DVD should be multi-sensory. This means what babies see and hear on-screen must go together logically. In addition, babies and toddlers should be encouraged to say the words they hear, and do the physical actions they see. This multi-sensory approach is very important because many of the baby’s new brain connections go from the visual cortex to the auditory cortex. If what the baby would see and hear do not match, then parents should avoid showing that program to their baby. Many DVDs show visual images (related or random), while playing music or other sounds that do not go with those images. This means that new synapses will not join logically. (In those cases simply listen to the music without showing it on TV, if you want your child to hear those songs.)
3) The DVDs should actually teach children something of lasting value. Many baby videos have little content of any value, besides entertaining the baby while the parent is busy.
4) The DVDs should be designed to teach babies language skills in addition to teaching other topics. For instance, the DVD could teach babies about shapes, but at the same time there should be words spoken that describe the shapes. This will help the baby learn language skills. As mentioned repeatedly in this guide, research indicates that the “natural window” for language development is 3 months to 4 years. Certain popular baby DVDs have very little spoken or written language. If you are showing your baby a DVD that doesn’t use language, then you shouldn’t expect your baby to learn any language skills while watching the DVD. Believe it or not, one of the most popular series of baby DVDs uses very few spoken words. Some have zero spoken words, so the babies will learn zero language skills from watching those DVDs.
5) Watching the DVDs should be a better option than the others available for the parents. If a parent is caring for a baby alone, there are times when letting the baby watch an interactive, multi-sensory DVD that is teaching an important concept is much better than leaving the baby to sit alone while the parent is on the phone or computer, cooking, or otherwise not interacting with the baby.
http://www.teachyourbaby.com/5-conditions-that-make-baby-or-toddler-dvds-helpful/