Hypothesis: This is a culture of affirmation.

Self-esteem and individualism rules; at any given point we are told it’s paramount to believe in ourselves, to know that what we are doing is ‘ok’. This affirmation works both ways. In any conversation, I would nearly guarantee that your fellow converser is nodding along to what you say, murmuring “mmmhmmm”s or “yeah, yeah”s; pick at random from a list of affirming gestures or statements — you probably have faced one from the person you are speaking with.
So what happens when we take it away? Just a steady, focused stare — no statements until the person opposite you stops speaking. This isn’t to say you lack animation, but rather you hold off on any type of affirmation or negation or feedback until the person has stopped speaking. I had hoped that such focused attention would make people feel as if they were being attended to with great focus. Unfortunately, the opposite follows.
Three friends became my guinea pigs.  I sat them down for lunch or dinner one-on-one:

Person A:

Person B:

Person C:

Blacked-out : the change.  Person A it was her eyes — constantly moving, unable to keep eye-contact.  Person B stated post-experiment that she noticed nothing.  She is fine.  Person C it was rather not her at all, but me that she found to be at fault.

I have the pleasure of being friends with each of these persons, so it was clear to me deviations in our normal patterns of conversation.  Across all three, regardless of their feedback, I could watch as statements that would come across strong, firm, assertive, trailed slowly of into questions given the absence of a nod of my head or a sprinkling of affirmation of their words.  The intonation of a statement became a question.

More surprisingly (though ad-hoc I suppose I am not surprised) it seems that the persons A and C noted that my intention — to appear more focused on them than usual — fell far short of the mark.  Rather, they both noted that I seemed to not be paying attention at all.  Person A specifically thought I was deriding her statements, judging her, implicitly telling her to stop.

Most startling: in the end I was the most uncomfortable — to not affirm someone else’s words caused me great strain and tension.

It seems that just listening isn’t quite good enough.  For you or me.