Camilla and I are both right-handed, but we hold the baby in different orientations. She holds Helen with her head to the left, I with her head to the right. My choice of orientation was originally driven by the perceived weakness of her head, which I felt needed the support of my right hand, and was reinforced by the nappy bucket being to the left of our changing table, so having her head on the right meant a shorter journey for soiled nappies. Helen was soon able to support her own head just fine, of course, but habits once started are hard to change.
We also have radically different ways of putting Helen to sleep. Camilla cuddles and rocks her on the glider chair until she is so soundly asleep that she can be transferred to the cot without waking. I walk backwards and forwards with her on my shoulder until I think she is relaxed enough, going by her breathing, then plonk her into the cot and try what I call "breathing her to sleep", which involves holding her hand (or both hands if she is unsettled or flailing) and taking long, deep, audible breaths — almost as if I'm meditating her to sleep, working on the idea that if I'm relaxed myself she will sense that. Camilla's approach has the advantage of being able to calm a really distressed baby, but mine has the advantage of being much faster when it works. The combination is often effective.
And we play with Helen in different ways. Here diversity might also be useful, though worrying about "enough stimulation" is probably silly at this age. Which leads me to some thoughts on why the first six months of a baby's life are so important. Most early infant development unfolds according to a fairly fixed schedule, and while deprivation — nutritional or emotional or social — or exposure to dangerous substances can interfere with that, there's no evidence that fine-tuning the environment makes any significant difference.
So why are the first six months or so so important? Because in that time the parents fix a whole range of habits, attitudes, patterns of behaviour and so forth that are going to affect the child's future. As well as establishing ways of interacting with their child, they also reconstruct their relationship with one another and form new social links. Choices may also be made about going back to work, nursery care, additional siblings and so forth.
Helen's progress is so well monitored and recorded that one day it might prove to be a valuable guide to bringing up babies. You and Camilla's scientific background must have something to do.
Yep. It's the kids controlling us and it takes the first few months to realise this. :D