The interview would be listening with almost full attention as you start speaking.
After 10 seconds, he would be listening with lesser intensity.
His mind will begin to wander after sixty seconds and he would devote half the attention to what you say. He will start asking you questions based on your responses and will start formulating his next set of questions.
After about 90 seconds, the interviewer would hardly be listening at all.
The attention level of an interviewer cannot be detected because most of them are skilled at looking at you and nodding in order to disguise the fact that their minds are wandering. When your answer is long the interviewer would not be listening any longer by the time you reach to a critical conclusion. This would be particular critical when you are telling the interviewer about yourself because there would be a lot to tell and it can be difficult to decide what part of it would be interesting for the interviewer.
Your Questions Are Important
By the end of your interview it would be important to ensure that you ask the right questions to keep the interviewer engaged.
Skilled interviewers would pose several behavioral event related questions and ask you to describe examples specific to your experience. Your response may easily be more than 90 seconds long in such situations. You can interrupt yourself in such cases by asking questions to the interviewer about what type of examples they are looking for and how detailed they should be. This will reengage the interviewer.
Interviewers tend to be impressed more by the questions you ask rather than your selling points. At the end of an interview, if a prospective employee asks you about the questions you want to ask, it can be frustrating if you are not prepared with any. It is therefore important that you prepare a list of questions well in advance.
Asking the right questions will also provide you strategic edge. Most candidates are only interested in talking about themselves so you can get an edge above others if you can get the interviewer talking about himself/herself.
Your goals in an interview should be to ensure that you would be understood well in an interview and that you present your talents in the best possible way. Engage your interview by asking intelligent questions to ensure that they would be listening intently when you provide a response.