Emotions are a sense like sight and hearing

I think your metaphor is well-taken. I always wondered how Data (from Star Trek) be the character he was in the absence of emotions i.e. how he could 'see' and 'feel' certain things (like duty, friendship) without a capacity for emotion. But I would have a question about the role of belief in emotion: doesn't the power of the emotion to disclose (moral) reality partly depend on the belief that informs it, and given a different belief (or belief system), the emotional response will change. Consider this passage from Tolstoi, "What I Believe":

"Five years ago I began to believe in the doctrine of Christ, and in consequence a great change has been wrought in me. I now no longer care for the things that I had prized, and I have begun to desire things concerning which I had formerly been indifferent. Like a man who, going out on business, on his way suddenly becomes convinced of the futility of that business and turns back; and all that stood to the right now stands to the left, and all that was to the left is now to the right; his wish to be as far from home as possible is changed to the desire of being as near home as possible – so, I may say, the whole aim and purpose of my life has been changed; my desires are no more what they have been. For me, good and evil have changed places."

This indicates to me the dependence of emotion on belief. What do you think?

If what you're saying is that you might feel a certain way at first, but that said feeling will change as you change your thinking, then I would agree. But it doesn't matter what you think in the meantime. As long as you feel a negative emotion while thinking a good thought, then you will still not see any good value in your life.

Could you give an illustration of the last point? And not sure I understand why it doesn't matter what one thinks in the meantime - Is you point that some positive emotional response to something in life a necessary condition of seeing any value in life, whatever anyone happens to believe? We know what is valuable (to us) through emotion?

Yes, you are correct. That is my theory. Even though we can't see any real value in our lives without our emotions, I would still recommend, for example, saving your own life or the life of one of your family members in danger even if you were completely apathetic.

Your metaphor makes no sense, at all. There is no logic that connects any of these statements in a meaningful way...