Voiceprints

Over one hundred years ago a scientist developed a visual representation of what the spoken word would look like. It was all based on pronunciation and showed that there were subtle differences amongst different people, even when they were repeating the same line. In 1941 the sound spectrograph was produced, a machine for mapping a voice onto a map. This machine analysed sound waves and produced a record of voice patterns showing frequency, intensity and time. By the late 1960s voiceprints were being used in criminal investigations.

Now voiceprints are used widely, especially in cases involving threatening phone calls and bomb threats. The telephone calls can be input into the sound spectrograph and analysed. The results given out can then be compared to another record. When two voiceprints are compared one of these five conclusions are reached; Positive identification, Probable identification, Positive Elimination, Probable elimination, and No decision. Voiceprints have been proven useful by playing major parts in past legal investigations.

The Polygraph

The Polygraph, more commonly known as a lie detector, is a machine usually used in legal investigations to determine whether the subject is lying or not. The polygraph tests three aspects of the human physiology; Respiration, Changes in skin resistance, and Pulse rate. Generally, when a person is not truthful, certain changes take place in the body. These are increase or decrease in blood volume, increase or decrease of heart rate, and a change in respiration and perspiration. These changes can be brought on by a number of things, such as nervousness or anger.

Whilst the polygraph test is being carried out, a set of results are recorded. These show the subject's physiology, and from these results we can determine whether or not the subject is being truthful.

But however useful the polygraph may seem, it has not proven to be a reliable tool. Though the test generally does work as planned, some individuals have a better control over their body than others, and can "beat" the lie detector test.