Palatograms

A palatogram is an image of the region of the upper surface of the vocal tract contacted by the tongue due to a consonant. The best way to obtain such an image is to coat the tongue with a mixture of equal parts olive oil and activated charcoal powder and record the resulting transfer of pigment.

The process is as follows:

• To protect the subject, one should use latex type gloves and preferably a surgical mask.
• Mix the olive oil and the activated charcoal powder.
• Apply mixture to the speaker’s whole tongue with a paintbrush or Q-Tip. NOTE: In case of dripping, one should cover the speaker’s clothes before applying the mixture.
• Ask the speaker to produce a word that contains the target sound (The word should not include any other sounds that make contact with the palate).
• Use a mirror (preferably a sterilized inter-oral mirror), and place it inside the speaker’s mouth at a 45^O angle with respect to the plane of the teeth.

Fig 1: Diagram showing relative position of the elements required to record the palatogram.

• Use a camera or video camera to photograph the mirror’s reflection of the place of articulation depicted by the imprint.
• If a video camera is used, the image can be transferred directly to a computer for further processing as described in “How to Capture Video for use on the Mac.”
• Once the image has been recorded, have the speaker rinse out his/her mouth with lemonade (or lemon juice in water).

Fig 2:  Palatogram; still image digitized from video.  Orientation:  Upper teeth are shown at top and reflected in the mirror at bottom.