This figure is basically the same as the last figure but it highlights the portion of the noise curve that will lead to false alarms and the portion of the signal + noise cure that leads to hits. Recall that when a the sensory signal is stronger than beta, the subject will respond that the signal is present regardless of whether the signal is present or not. So when the noise is greater than beta the subject responds "present". That region of the noise curve is highlighted in red below. Correct rejections occur the rest of the time that only noise is present and that is indicated by the dark blue below. If this seems odd to you that a person would respond that the signal is present when the signal is not present, you need to realize that the person does not know that the signal is present or not. All that they know is that there is some activity in that sensory dimension and that a signal might be present. They have to make a decision as to whether the signal is present or not based on confusing information.
The hits and misses work the same way as the false alarms and correct rejections do but on the signal + noise curve. You can manipulate this figure just as you did the last figure so try it out and watch particularly what happens to the hits and false alarms.