How to do Static Palatography

Palatograms	Making Midsagittal Diagrams	Practical Points
Linguograms	Making Tomographic Slices	References
Making Dental Alginate Impressions	Superimposing Contour Lines

Palatograms

Palatography is a well known traditional method of obtaining articulatory data. The best method of determining the region of the upper surface of the vocal tract contacted by the tongue in a given word consonant is to coat the tongue with a mixture of equal parts of olive oil and powdered digestive charcoal. Use a sterilized, wide, soft paintbrush to apply the mixture to the entire top surface of the tongue, as far back as is comfortable for the speaker, as well as to the vertical part of the tongue tip. Then ask the speaker to say a word containing which contains the sound to be investigated, but which contains no other consonants made in the same articulatory region.

When this has been done, the marking medium on the tongue will have been transferred to the upper articulator. Insert a mirror whose corners have been rounded, and which is wide enough to reflect both the left and right upper molars (50-60 mm) into the mouth, and use it to view and photograph the place of articulation.

Once the articulation has been photographed, ask the speaker to rinse out his or her mouth. 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 .”

Linguograms

When all the required pictures of the roof of the mouth have been obtained, the procedure can be reversed to produce linguograms. Paint the upper surface of the mouth with the olive oil and charcoal mixture and observe (and photograph) the part of the tongue that is making the contact. It may be necessary to instruct the speaker to move the tongue up, down or to the side, to show sublaminal contact, or contact on the sides of the tongue.
Note that speakers' tongues differ in their absorbency to the charcoal mixture. For speakers whose tongues begin to collect black color despite repeated rinsings, it is preferable to begin by painting the roof of the mouth and obtaining the linguograms first, since repeatedly painting the tongue can cause loss of contrast.

Palatograms and linguograms are shown in Figures 1 to 3.

Fig 1: Palatogram; still image digitized from video. Orientation: Upper teeth are shown at top and reflected in the mirror at bottom. Fig 2: Linguogram showing tongue blade and body contact. Fig 3: Linguogram showing tongue tip contact and sublaminal contact (contact under the tongue.)

Note that in both kinds of photographs the black contact areas reflect the sum of the articulatory contacts that occurred in the pronunciation of the word investigated; they do not show the tongue’s position at any one particular moment. In addition the photographs of the tongue usually show it when it has been slightly stuck out of the mouth, and is therefore not in the same shape as it was when producing any of the sounds.

Making Alginate Dental Impressions

Palatograms and linguograms should always be accompanied by diagrams showing the shape of that particular speaker's mouth in the form of a traditional sagittal section. Diagrams of this kind can be based on dental impressions of the oral cavity made in the field. Use chromatic dental alginate as the impression material; other substances which set harder and cannot be cut are of no use. There is no reason for these impressions to be made using a tray of the kind that dentists use, which takes an impression of the outer surfaces of the teeth. The outer surfaces of the teeth play no role in the production of speech, so they can be neglected. All that is needed is an impression of the inner surfaces of the teeth and roof of the mouth.

Chromatic dental alginate has different color phases during mixing (purple), setting (pink), and set (green), which makes timing while mixing and setting unnecessary. The easiest way to make an alginate impression is to mix a sufficient quantity place 3 or 4 tablespoons of powdered alginate in a flexible plastic container and gradually add water while stirring, until the mixture turns from purple to pink and a thick paste results. Gather the alginate in a plastic scoop and transfer it to the end of a palatography mirror. Ask the speaker to lean slightly forward so he is looking at the floor and breathing through his nose, and while the alginate is still in its setting phase (pink) carefully place the mirror and mound of alginate into the speaker’s mouth. Instruct the speaker to bite down on the mirror until it is firmly pinned in the occlusal plane between the upper and lower teeth, to continue breathing through the nose, and Press the mirror firmly against the upper teeth, to allow some of the material to flow out of the mouth around the upper lip. INSERT PIC. A good impression for phonetic purposes should be made with sufficient material to indicate (at least roughly) the shape of the upper lip and the curvature of the soft palate. The palate will, of course, be in a lowered position, as the speaker will have been breathing through the nose while the impression material is setting. The impression material around the lips sets slightly more slowly than that inside the mouth, where it is slightly warmer. When the alginate has set (turned green) you can see that the material around the lips is firm, it is quite safe to ask the speaker to gently remove the impression by rocking the mirror remove the mirror from the mouth, first rocking it back and forth, and raising and lowering it slightly, so as to break the seal. Then ask the speaker to rinse his mouth several times to remove any remaining alginate.

If an alginate impression is to be kept for any length of time it must be immersed in water so as to prevent it from drying and shrinking. Otherwise, slide it off the mirror with a flat metal baking spatula or knife (Figure 5a.) . and trim the base flat so that it is parallel to the plane of the teeth. If the mirror really was pressed firmly against the upper teeth while the impression was being made, this should involve no more than the removal of Remove excess material from around the sides, including the negatives of the teeth. (Figure 5b.) The impression may then be cut in half in the mid-sagittal plane (Figure 5c), and a tracing of the upper surface made, to yield a profile image of the shape and size of the palate (Figs 5d and 5e.) The exact positions of movable structures such as the lips and the soft palate have to be estimated, but if care has been taken to have sufficient impression material around the lips and as far back in the mouth as possible, the sagittal diagram will be reasonably accurate. Palatograms should always be accompanied by diagrams of this kind, as in the illustration ***** PL please supply. It has long been established that sagittal sections provide the most useful representations of speech sounds.

Fig. 5a Fig. 5b Fig. 5c

Fig 5d Fig 5e

Making Midsagittal diagrams

The impression of the roof of the mouth may also be used to construct contour lines at fixed distances from the plane of the teeth. A line showing all points 10 mm above the plane of the teeth below the highest point of the palate has been superimposed on the palatogram in ****** PL please supply. In order to draw such a line put the two halves of the impression material together again, and trace round the base of the teeth. Pic of doing this?

. Next, bisect the impression in the coronal plane, at a point about the middle of the impression (usually between the second premolar and first molar.) insert pic of doing this. The intersection of these mid-sagittal and coronal cuts can be used to define x and y axes and an origin on a piece of graph paper.

Making Tomographic Slices

Slice each of the resulting quadrants horizontally, 5 mm above the plane of the teeth (i.e. with the blade of the knife parallel to the surface of the impression material corresponding to the plane of the teeth). It is then possible to measure the distance of this plane from the roof of the mouth, and to draw a line round it. In order to assist with the scaling it is also advisable to draw round the base of the teeth. Check with your local biology or physical anthropology departments for a tomograph with which to make the 5 mm horizontal slices. Otherwise, it is relatively easy to make a tool to cut the alginate mold parallel to the plane of the teeth. On a flat, smooth, 190 x 125 mm wooden board paste heavy cardboard strips parallel to each other, 70 mm apart, resulting in a two “walls” of height 5mm. On top of, and perpendicular to the cardboard walls place an 80 mm long razor blade, creating a wide slicing area. Push each quadrant of the dental impression through this tool so as to cut off the bottom 5 mm of impression material in the occlusal plane. Place the quadrants back together at the origin on the graph paper, trace them, and repeat the process until all of the impression material is drawn in this way. show graph paper. insert pic ritopo.

Superimposing contour lines on photographs

To superimpose the contour lines and the marks of the teeth accurately on the photograph, it is first necessary to be certain that the photographs are not distorted. They will be foreshortened, if the mirror was not at a 45? angle to the plane of the teeth. BLS angle PIC.

The scaling can be done quite easily if the photograph has been entered into a computer, either by scanning it, or by conversion from the video. The contour lines, location of the teeth and the tracing of the sagittal section can also be scanned in, and then the image of the roof of the mouth scaled independently in each direction so that obvious landmarks, such as the distance between certain teeth are adjusted appropriately.

Practical Points

There are some practical points in connection with palatography that should be noted. Firstly, care should be taken in selecting appropriate words. We are often interested in comparing the places of articulation of different sounds. Accordingly words must be chosen that contain these articulations, and do not contain any other similar articulations that might overlap with them. Thus when investigating the difference between s and sh in English one should use words such as “sop-shop” rather than “sot-shot.” Similarly one should use either a range of vowels (“seep-sheep, sip-ship, same-shame, Sam-sham, sop-shop, etc.”) or, if this is not possible, just open vowels which might be expected to have less effect on the consonant articulation. As with all instrumental phonetic investigations, time spent selecting suitable words is a good investment.

When doing palatography, one should allow the speaker to practice the task extensively. It is important to get the speakers to relax after the tongue or upper surface of the mouth have been painted, so that when they say the word being investigated they do so naturally. It also requires practice to stick the tongue out of the mouth the same way every time. It is obviously important to date and label the photographs as soon as they are taken. In addition, again as with all instrumental data, it is preferable to make records of several different speakers saying a few utterances rather than one or two speakers repeating a large number of different utterances. Ideally one would like to get a dozen speakers of the same dialect each repeating a dozen times all the contrasts to be investigated. But making palatographic records is fairly time consuming, and in a world in which time and effort are limited one may have to be satisfied with half a dozen speakers saying each word once. We hope, however that gone are the days when phoneticians such as Ladefoged made general statements about some West African languages based on the palatographic records of a single speaker of each language. We need to find out the properties of the language that a group of speakers have in common, rather than the details of an individual’s pronunciation.

[Adapted from:
Ladefoged, P. (1997). “Instrumental techniques for linguistic phonetic fieldwork.” In W. Hardcastle and J. Laver (Eds.), The Handbook of Phonetic Sciences Oxford: Blackwell Publishers.
and from:
Anderson, V. (in progress) “Connecting Phonetics and Phonology: Evidence from Western Arrernte”. UCLA Ph.D. dissertation.

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Fig 1: Palatogram; still image digitized from video. Orientation: Upper teeth are shown at top and reflected in the mirror at bottom.	Fig 2: Linguogram showing tongue blade and body contact.	Fig 3: Linguogram showing tongue tip contact and sublaminal contact (contact under the tongue.)