We may say that whatever attracts our attention in the sphere of any sense, sight or sound, touch or smell, surely becomes more vivid and more clear in our consciousness.

This does not at all mean that it becomes more intense.

A faint light to which we turn our attention does not become the strong light of an incandescent lamp.

No, it remains the faint, just perceptible streak of lightness, but it has grown more impressive, more distinct, more clear in its details, more vivid.

It has taken a stronger hold of us or, as we may say by a metaphor, it has come into the center of our consciousness.
But this involves a second aspect which is surely no less important.
While the attended impression becomes more vivid, all the other impressions become less vivid, less clear, less distinct, less detailed.
They fade away.