Let’s continue with talking about the notion of distance.
……….2) ECHO / DISTANCE :
When we are in a mountain area ant that we are shouting, we can hear an echo which returns to us. If the time between the vocal emission’s moment and the return to our ears is superior to 60 milliseconds, then we can perceive an echo.
« We can hear the time between two acoustic signals. If it’s superior to 60 milliseconds, we can hear an echo : there is a hearing separation, i.e. an interval between a sound and its return. This distance in the air is twenty four metres, and it corresponds to a reverberant wall located at 12 metres and further »(1).
Example : let’s consider 70 milliseconds (in order to be superior to 60 milliseconds and make the calculation easier). In the air, the sound speed is about 340m/sc. As x = st (distance x, speed s, time t), we have x = 340 x 0.07, so almost x = 24 metres. If the sound traverses these 24 metres back and forth, then we can conclude the reverberant wall is located at 12 metres.
So, the notion of distance exists thanks to the echo.
« It seems obvious that ear is the door of verbal language, at such a point that we forget it’s far from being its key function. Indeed, we have to distinguish the ear’s secondary function within acoustic elements’ transmission which will be used in communication codes, from ear’s primary function which runs it, and which is the function of environment’s perception. Not only the sounds’ direction depends on ear, but also the distance is acoustic. That’s the echo and its time interval which provide us, from the very first months, indications about objects’ distances reflecting the acoustic wave. Sounds’ absorption and their non-reflexion bring a feeling of depth, « a vagueness of infinite ». The deaf child does not have this dimension of the world. The distance of objects is unknown to him. The vision only supplements it through conditionment, in the frame of the creation of perspective. The world has no depth, to the deaf child »(1).
« The deaf child… has difficulties to know the distances, he bumps into objects, he needs to come into direct contact with elements to realize there is something before him. To him, the outside world is structured without one of its very important aspects »(2).
« We can see it in special kindergartens. When children bump into objects and things, they can hardly plan the dynamics of their displacements. Concerning the assessment of the prehension gesture, Shirley Vinter highlighted a significant difference between a hearing person and a deaf person »(3).
(1) Professor J.C. LAFON « Les enfants déficients auditifs » / « Hearing impaired children » page 19.
(2) Professor J.C. LAFON « Text about language – Oral presentation – Délémont 1977 » page 61.
(3) Professor J.C. LAFON « Les enfants déficients auditifs » / « Hearing impaired children » page 104.
(translated from french by E.F.)