LAFON 46A THE PRIMARY HEARING (road to language) part 6

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At last but not the least, let us talk about volume.

………. 3) SOUND REFLECTION / VOLUME:

Sound reflexion may be heard up to 5 milliseconds between the time a vocal production occurs, and the time to hear it back. That is equivalent, in the air, to an approximative 2 meter distance of sound travel – and thus, to a 1-meter distant object.

Here is an example: let’s consider a 6 milliseconds time frame – so that we are above 5 milliseconds, which facilitates calculations. In the air, time travels at about 340m/s. Since d = s.t. (d being the distance, s the speed and t the time), we get d = 340 x 0.006, i.e. d = 2 meters. In order for the sound to travel these 2 meters back and forth, the reflecting wall should be should be 1 meter far.

« When we thump the table or talk in a room, we get acoustic shapes that are specific to the object and the room. Speech sounds different in different rooms, there are some echoes, some sound reflections that depend on the room volume, on the distance or height… and that give various shapes to the sound »(1).

« When we close our eyes, wa can still know where we are, whether there is a hign or low ceiling, we can have an idea of the distances, detect whether the room contains any aperture, panel or closures, as all these are part of acoustics. That is the – very psychological – reason why some people feel uncomfortable inside the audiometric test booth: they can feel there are walls but no sound reflections, it’s like being in an infinite environment while they are completely aware they are sited in a closed environment, and it is very unpleasant to have a mismatch between we see and what we hear. That is unpleasant because hearing takes the advantage over the vision in the way we organise and perceive volumes »(2).

« The volume of our surroundings is an intricate mix of echoes ans sound timbres ramarkably tuned with time. Deaf children have no notion of the volume of the place(s) where they move and live. Indeed, the whole structuration of space perception is troubled in deaf children, far before the question of speech arises. And we can hardly figure out how it feels to live in a two-dimension environment, as our perception of space is deeply embedded within our early childhood. We only realise how important these notions are when we are deprived from them, before that,we don’t even notice them as they are basic constituents of our daily life. In acquired deafness, where the representation of the external world is clearly organised, vision compensates the impaired perception of distances and volumes »(3).

JYM

(1) Professor J.C. LAFON « talk on language writings, Délémont 1977 » page 15.

(2) Professor J.C. LAFON « talk on language writings, Délémont 1977 » page 16.

(3) Professor J.C. LAFON « hearing-impaired children » page 19.

(translated from french by O.B.)

Jean-Yves MICHEL

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