Exposure
"Even some thirty years ago reports appeared that indicated that children taught sign language had acquired about seventy-five signs by the time they were nine months old. In contrast, the typical child of that age could understand fewer than ten words, regardless of how bright she was." -- Dr. Burton White, in the foreword to Sign with your Baby, by Joseph Garcia
"Market research has found that children often recognize a brand logo before they can recognize their own name."
-- Eric Schlosser, Fast Food Nation