Although there are some good answers already, I thought I might add this comment.
Although one is not aware of this, one’s brain is continually processing incoming sound. (Otherwise, one would not be able to notice when an interesting or important sound came in.)
“The conversation on the TV caught my attention; it was about the night of the murder.”
[You have only one attention [poor grammar there], but your brain/body continually processes sensory input such as sound [noting that human female brains have hardware for processing two sound sources simultaneously], balance, pain and seen movement. Thus, your attention would be on something else, and your brain would note that something had been said on the TV that was of interest to you (analogous to, for instance, a sudden pain in your toe), and you would then transfer your attention to that.]
In the same vein:
‘Suddenly I noticed one phrase amidst the babble coming out of the TV — “inside the building”.’
Incidentally, this is not the word you want, but… the word “salient” relates to the term “protrude” here; something is salient if it is apt to be noticed (amidst the sea of things that you see/hear/etc. but do not pay attention to). For instance: “The salient thing, to Detective Smith, was that Mary never once mentioned that the painting was worth only about $5.” (This is an example in which something is salient in a more subtle sense — the detective noticed, and thought it important, that something was absent.) A simpler example: “The salient thing for Barbara was that she and Sally had identical dresses on — so much so that she could remember nothing else about that night.”
