Complex sentence: But when it is followed by a second stimulus soon after, the response to the second stimulus is blunted and this is an adaptive mechanism to prevent overstimulation and to help to focus on a stimulus among a host of other distracing stimuli.
Split into simpler sentences: But when it is followed by a second stimulus soon after, the response to the second stimulus is blunted. It helps to focus on a stimulus among a host of other distracing stimuli.