Licence: In copyright
Credit: The child's hearing for speech / by Mary D. Sheridan. Source: Wellcome Collection.
![late Dr. Phyllis Kerridge of University College Hospital, London in her report Hearing and Speech in Deaf Children [2], eoaeideres the ‘middle frequencies’ (512, 1024, 2048 cycles) to be the most important for speech recognition; but Dr. and Mrs. Ewing, who have been practising audiometry at Manchester Wuiversity siuce 1927, suggest in their book The Handicap of Deafness |3| that a minimum range of 250 to 5,000 cycles is necessary for accurate appreciation of speech. RIGHT EAR LEFT EAR 9747 128 256 $12 4024 2048 4096 8192 9747 FREQUENCY IN CYCLES PER SECOND THE AUDIOGRAM BLANK FIG. 2 The numbers on the vertical scale represent the intensity level of sound in decibels. A sound that is too weak to be heard is said to be outside the ‘ threshold of audibility ’,~ The tone that is so strong that it causes discomfort is said to be approaching the ° threshold of pain’. Between these two extremes (which differ for each indi- vidual) stretches the ‘ auditory field’. Dr. R. Ty Beatty imi his book Hearing in Men and Animals [4] gives a very interesting ‘Ladder of Noise’, demonstrating in homely equivalents the steps between 10 decibels, the intensity level of the faintest audible sound,](https://iiif.wellcomecollection.org/image/b32744419_0025.jp2/full/800%2C/0/default.jpg)
