The paralinguistic channel of communication is defined as speech characteristics falling outside of the spoken word. Just as a subject's nonverbal behavior can completely alter the meaning of words within a verbal response, paralinguistic behaviors can modify the meaning behind words. Consider the following conversation:

Joe: "Hey Mike, I've got to pick my kid up from baseball practice in a half an hour. Would you mind staying late to write this report?"

Mike: "Oh sure. No problem."

To illustrate the significance of paralinguistic communication, read Mike's response out-loud first in a sincere manner, where Mike does not mind writing the report at all. Then read Mike's response in a sarcastic manner, where he expresses clear resentment in being asked to write the report. If you are like most people, you altered your voice inflection, as well as rate and pitch to send two different messages using the same words. During an interview, monitoring a subject's paralinguistic behaviors can offer great insight into the true meaning behind the words used in a response. A number of paraliguistic clues have been identified that relate to a subject's truthfulness or deception. The following discussion relates to only three of these.

Response Latency

Response latency is defined as the duration of time between the last word of the investigator's question and the first word of the subject's response. Research reveals that the average response latency for truthful subjects is .5 seconds, whereas the average latency for deceptive subjects is 1.5 seconds. Especially when a subject is asked a straight-forward question such as, "Last night did you see Jimmy at all?" a denial that comes after a two or three second delay should be viewed as highly suspicious.

An extended response latency is the result of the subject mentally deciding whether to tell the whole truth, part of the truth, or a whole lie. Often a deceptive subject will attempt to fill this period of silence by repeating the interviewer's question, e.g., "Did I see Jimmy at all last night? No, I did not." Another common technique to stall for time is for the subject to ask the investigator to clarify a question:

I: "Did you have sexual contact with your step-daughter?"

S: "What exactly do you mean?"

I" "At any time did you have sexual contact with your step-daughter?"

S: "Oh no. I would never do that."



An extended response latency is not always an indication of deception. Consider the subject who is asked a hypothetical question that requires thought or a judgment. An example is, "Who do you think may have had sexual contact with your step-daughter?" Because this question calls for speculation, the investigator should be suspicious of a response that is voiced too quickly, e.g., "I have no idea." On the other hand, a subject innocent of the crime may very well take a couple of seconds before offering the sincere response, "I have no idea."

Volume Changes

When someone is telling the truth, he wants to make certain that the investigator understands exactly where he stands. Consequently, during an accusatory interrogation, a truthful suspect's denial is often spoken loudly and distinctly, perhaps with a emphasis on each word, e.g., Listen, I did not have anything to do with that robbery! On the other hand, when these same words are spoken at a conversational level, especially with the suspect looking down at the floor, they do not sound nearly as convincing.

Increasing one's volume, of course, is a natural defensive response to guilt or anxiety. Most investigators have encountered the deceptive suspect who engages in a loud tantrum in the hope that the emotional outburst will fend off further questions. The focus of this tirade is not centered around the suspect's non-involvement in the crime, but rather, some threat against the investigator (law suit, letter to the editor of the local paper, "I'll have your badge for this"). Consequently, an increase in a suspect's volume must be considered in context with the questioning environment. A suspect who loudly protests his innocence when being asked non-accusatory interview questions is less credible than one who engages in the same behavior after being accused of committing a crime.

A decrease in volume during the course of a response can be a very significant behavior symptom of deception. This behavior is referred to as "losing interest in a response." During our training seminar we show an interview of a deceptive suspect who is asked, "How do you feel about being interviewed concerning this missing $1000?" The words the suspect uses in her response to this question appear to be more typical of the truthful. She answers, "Well, I certainly understand why I was asked to go through this. It's a lot of money to come up missing and I'm willing to do whatever it takes to get to the bottom of this." However, when listening to her response, it is very evident that the last thing she wants is, "to do whatever it takes to get to the bottom of this." During that portion of her response her volume drops significantly to the point that the last portion of her response is barely audible. The suspect had lost interest in her response -- she said the right words, but there was no conviction or sincerity behind them.

Rate Changes

When a subject offers a spontaneous response, it should be free-flowing and the rate of speaking should be maintained. When the account concerns an emotional event, such as being the victim of a sexual assault or armed robbery, the truthful victim's rate of speaking will increase, as true emotions are recalled.

Conversely, a decrease in rate often indicates that the subject is editing information from the account, or fabricating information within the account. Both of these mental activities (editing and fabrication) require time and to buy time, the subject slows down his response rate. A caveat to this statement is the traumatized victim. A victim interviewed shortly after an emotional event may exhibit a decreased rate when speaking simply because he is presently dealing with the emotions of the event. However, after a victim has been given a reasonable period of time to adjust to the event, a decrease in response rate when relating the incident to an investigator should warrant suspicion as to its truthfulness or completeness.

As with all of our investigator tips that address the interpretation of a subject's behavior, the investigator must consider internal and external factors which influence a person's behavior before attaching significance to a particular behavior symptom.