I've noted a wide range of responses in the people I know from those who readily go into a world of their own to those who are very mindful of everything going on around them.

I prefer mindful people. Those who are independent in mind and behaviour tend be more mindful in my experience. People often wonder how it is that I open the front door of the house before they have a chance to press the door bell but the garden gate squeaks, not very loudly, and it registers in my brain even if I am working quiet hard on the computer. Often my guests did not even notice the gate squeak themselves, not being very mindful.

Like most other things, mindfulness is a choice. If you choose to block out the world then after a while it can't get in even when you want it to...I note that in highly novel situations one can not process all the available sensory information and much is missed regardless of one's degree of mindfulness...

"Like most other things, mindfulness is a choice. "

So you deny physiology?