~~355. J. Physiol. (I957) I37, ( Ophthalmological Research Unit, Institute of Ophthalmology,

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1 am ~~355 J. Physiol. (957) 37, ( PTCH DEPENDENCE ON NTENSTY N UNLATERAL DEAFNESS WTH RECRUTMENT OF LOUDNESS BY PRSCLLA H. STRANGE From the Visual Research Division, Medical Research Council Ophthalmological Research Unit, nstitute of Ophthalmology, Judd Street, London, W.C. 1 (Received 25 February 1957) Now that it is known to be abnormal for the pitch of a pure tone above 1 cs to depend on intensity (Strange, 1955, 1956) it becomes important to know more about those types of deafness which accompany this pitch defect, especially with regard to the abnormally large gain in loudness for a given increase in intensity which is known as recruitment of loudness. The technique of alternate binaural loudness balance (Fowler, 1936) is a sensitive way of exploring the loudness function of a deaf ear, but it can only be used when the subject has good hearing in the other ear. The author has studied a group of such subjects, and, in the course of extended tests, has examined the pitchintensity dependence for each ear separately, and has performed loudness balance tests as between the two ears. This paper is concerned with these experiments. METHODS The apparatu8 was designed to produce two pure tones each lasting for 1 sec in quick succession, the next pair of tones following after an interval of sec. The tones were produced by a pair of Hewlett-Packard 25 A.G. oscillators, and were independently controued in frequency and intensity. The two tones could be led to a single earphone, in which case the apparatus was exactly as described before (Strange, 1955, 1956), or else it was possible to lead the first tone ofeach pair to one earphone of a matched 426A S.T. and C. head set, and the second tone to the other. The same Amplivox audiometer was used as before. The subjectd each possessed one ear with very much better hearing than the other, and were selected on the basis of the air conduction threshold audiogram. The only thing in common between the defective ears of the various subjects was irregularity of the threshold audiogram, not its shape. Only one of these subjects had previous experience of the pitch tests, H.C.W. (Strange, 1956). One subject, V.P., was a woman. Technique. Pitch tests were carried out as described before (Strange, 1955, 1956) always using a single earphone and testing one ear at a time. Frequencies between 125 and 6 Cs were examined as follows. The subject heard a series ofpairs ofpure tones in one ear, and his task was to record a forced-choice comparison ofthe pitch of the second tone of each pair with the pitch of the standard first tone. This procedure is sometimes called the method of constant stimuli, and by

2 356 PRSCLLA H. STRANGE this method frequencies of the second tone may be found which, at different intensities, have the same pitch as the standard tone. Points representing these tones may be plotted on a diagram of frequency against intensity. f the pitch is independent of intensity, they will all lie on a line of constant frequency. The slope of a straight line fitted to the points is thus a measure of the degree of dependence of pitch on intensity (Strange, 1955). By testing the subject in each ear separately, the dependence of pitch on intensity could be compared for ears with different audiograms. Since each subject had one nearly normal ear, it was possible to do the alternate binaural loudness balance test (Fowler, 1936) and so to discover the degree of recruitment of loudness in the worse ear. The loudness balance tests were done after the pitch tests were complete, to avoid confusion between the two tasks. The apparatus was adapted to present the first tone to one earphone, on the worse ear, and the second tone to the other earphone on the better ear, so that the subject heard pairs of tones of the same frequency, of which the second tone varied in intensity. The subject was asked to compare the loudness of each pair of tones, and to say whether the second tone sounded 'louder', 'softer', or 'equally loud'. The intensities with which tones must be presented to the two ears, in order to sound equally loud, give the co-ordinates of points on the solid line ofthe Fowler diagrams of Fig. 2. The threshold of hearing of the better ear is taken as zero intensity. f the two ears were identical, of course, all the loudness balance points would lie on the dotted line symmetrically between the axes. n a case of complete recruitment of loudness, the threshold of hearing of the one ear is defective, but the same high intensity sounds as loud in the deaf ear as it does in the good ear. The solid line in the Fowler diagram will then meet and follow the dotted line, at high intensities. f there is no recruitment, the solid line will run parallel to the dotted line, displaced from it by the amount of the threshold defect. To give a single figure as an index of the degree of recruitment of loudness, a straight line was fitted to the set of loudness balance results at each frequency, and the reciprocal of its calculated slope taken as the recruitment index. This index is shown in Fig. 3, the points being joined by broken lines. Values less than 1 indicate recruitment of loudness. For each subject, the difference between the threshold of hearing of the two ears was found during the loudness balance tests, using the same apparatus. This difference is also shown in Fig. 3, joined by solid lines. The two graphs on Fig. 3 are on such a scale that a recruitment index 1 corresponds to no difference between the ears, and recruitment index 5 corresponds to a threshold difference of 5 db. The two graphs should lie close together if recruitment of loudness is complete by 1 db above zero. The method of calculation, because of the curvature of the loudness balance lines on the Fowler diagram, tends to make the recruitment index too small, rather than too near unity. RESULTS The results of pitch tests on both ears of six subjects are shown in Fig. 1. The two diagrams for a particular subject are side by side, that for the better ear being on the left. At the top of each diagram is the threshold audiogram, with circles, and the lower graph, with solid points, gives the slope of the lines of constant pitch plotted against the frequency of each standard tone. These diagrams are similar to those presented before (Strange, 1955, fig. 3, and Strange, 1956, fig. 2), but this time frequencies below 1 cs are included. As before, the unit of slope is 1-3 octaves per decibel, which means that one unit on the ordinate scale corresponds to a slope of 11 octave in 1 db. The slope is taken as positive when the pitch becomes higher as the intensity increases. The pitch change was always more marked for the ear with the irregular audiogram than for the better ear. This holds true where there is pitch-

3 PTCH AND RECRUTMENT OF LOUDNESS 357 dependence on intensity at frequencies below 1 cs. All such pitch changes at low frequencies, found so far, have been of negative slope, i.e. the pitch becomes lower with increasing intensity (see Morgan, Garner & Galambos, 1951). Both E.N. (L) and K.F. (L) have a range of frequencies, around 3 cs, where the slope is negative. Previously, a range of negative values of slope at such a high frequency has only been found associated with a dip in the audiogram at about the same frequency. The '4 cs dip' is often caused by a traumatic injury, so it is not unexpected to find similar results in the pitch tests from K.F., who dates his deafness from a severe blow on the side of the head. E.N. (L), however, has an 'island' of hearing at about 3 cs, and his audiogram bears a superficial resemblance to that of J.K. (R) yet the slope in the latter case is large and positive, the opposite of E.N. There is a small dip in the audiogram of E.N. (R), this subject's better ear, which suggests a possible traumatic injury, perhaps contributing to the unusual audiogram of his left ear as well. Fig. 2 shows detailed results of the loudness balance tests for one subject, H.C.W., using the method of presentation of Fowler (1936). Each solid line is drawn through a series of points whose co-ordinates represent the relative intensities with which the same frequency must be presented to each ear in turn, in order to sound equally loud. nspection shows that recruitment of loudness is almost complete at frequencies up to 15 cs, but at 4 cs there is some suggestion of a maximum attainable loudness. n Fig. 3, the solid lines join points which represent the difference between the thresholds of hearing of the two ears, as found with the loudness balance apparatus. (This is not necessarily the same as the difference of the audiograms, found some months earlier. Different apparatus was used on the two occasions, and the threshold of hearing may also change with time.) The broken lines join circles which represent the recruitment index at each frequency. The graphs are close together if recruitment is complete, whereas the broken line lies above the other if recruitment of loudness is not complete in the worse ear. The first diagram of Fig. 3 refers to the results of H.C.W., shown in more detail in Fig. 2. The incomplete recruitment at 2 and 4 cs is clearly shown by the divergence of the two graphs. The other diagrams show the degree of recruitment of loudness, in the same way, for the other five subjects. n general, there is good agreement between the solid and the broken lines in Fig. 3, showing that the deafness is of a recruiting type in every case. f the key to the production of pitch-dependence on intensity lies in the loudness function at all, it is in minor departures from the rule of complete recruitment that we must seek it.

4 358 PRSCLLA H. STRANGE 8 H.C.W. 4 _ n, -48 B\,--,,, ~%- -8- ^~.. A a - a 1' -- '--eo\o_o rh.l.w. ' _... A-, () L. O_ O "".O '. - J.F.C. QD %6 k.-.'x~~~ L \ ~ z~~~~~~~~~~~~~~~~~~~~~ vp 9 8 V.P. E 4 - w93l. A - v *-* O -8 L *- * T 4 ' Frequency (kcs) 8. N\o Frequency (kcs) Fig. 1. Threshold ofhearing, and the mean slope of the equal-loudness contours, against frequency. The diagram referring to the defective ear of each subject is on the right. The upper graph of each diagram is the audiogram, -, and the lower graph shows the calculated slope of a linear approximation to the equal pitch contour, plotted against the frequency of the standard tone, -*. The unit of slope is 18 octave per decibel. 8

5 PTCH AND RECRUTMENT OF LOUDNESS 359 _ O vs u U _E n 4 -'vo 4 ::= " o -o N 4 -\ 8 4 XV. \lf "*o _ o\j. - E.N. rj.k.(), - - ~d't g) _,. _,._. ~~~~~~ L - J.K. - a. L ~~~~~~ ~~~- 1 _\. '.O -8 J,,. l ".."- -,o- K.F. )o -o'o,_ - Fig. 1 (cont.). a a A T Frequency (kcs) 23 PHYSO. CXXXV

6 36 PRSCLLA H. STRANGE T'he results of the pitch tests and of the loudness balance tests for each subject may be summarized as follows: (1) For H.C.W. (L) frequencies between 125 and 5 cs become lower in pitch with increasmg intensity. The threshold defect is greatest from 15 cs upwards, but at 2 and 4 cs recruitment is not complete. The pitch moves away from the greatest defect. (2) For J.F.C. (L) frequencies between 125 and 1 cs become lower in pitch with increasing intensity. The audiogram slopes down from 1 cs to greater deafness at high frequencies, with complete recruitment of loudness except at 4 cs. The pitch moves away from the threshold defect. (3) For V.P. (R) frequencies from 125 to 2 cs become lower in pitch with increasing intensity. There is a hearing loss at all frequencies below 4 cs, with the greatest hearing loss at 1 cs. The threshold for 6 cs is normal. Recruitment of loudness is complete. The pitch moves towards the defective lower frequencies. 41 4, _ 25cs so _ : 5 Db left ear cs 111 * * a,.15cs 7, cs. - 2 cs OO , - 5 1( 5 o 5 1 " 5 1 Fig. 2. Loudness balance for one subject, H.C.W., at various frequencies. The co-ordinates of any point on the continuous line represent the relative intensities with which a frequency must be presented to each ear in turn, in order to sound equally loud. The broken line represents the case of symmetry, where identical tones sound equally loud in the two ears.

7 PTCH AND RECRUTMENT OF LOUDNESS 361 (4) For J.K. (R) frequencies from 1 up to at least 6 cs become higher in pitch with increasing intensity, the effect being greatest at 3 cs. There is a trough in the audiogram at low frequencies, maximal between 5 and 1 cs, and a narrow 'island' of good hearing at 4 cs. There is complete recruitment of loudness, except at 4 cs, where the loudness does not increase as rapidly with intensity as in the left ear. The pitch moves away from the defective lower frequencies. (5) For E.N. (L) frequencies close to 3 cs become lower in pitch, with increasing intensity. There is an 'island' of more normal hearing at about the same frequency, at which recruitment of loudness is not quite complete. The pitch moves away from this 'island' towards more defective lower frequencies. (6) For K.F. (L) frequencies close to 3 cs become lower in pitch with increasing intensity. Frequencies above 2 cs have a uniform defective threshold, but they may not all share the same degree of recruitment of loudness. Pitch moves away from the defective region. x._.1.e -A L 4' Frequency (kcs) Frequency (kcs) Fig. 3. Difference between the thresholds of hearing of the two ears of each subject, -**, lefthand ordinate; index of recruitment of loudness of the defective ear, -, right-hand ordinate (this is the reciprocal ofthe calculated slope of a linear approximation to the loudness balance graph). The scale is chosen to bring the graphs together where recruitment of loudness is complete. The common abscissa is frequency, in kilocycles per second. 23-2

8 362 2PRSCLLA H. STRANGE Conclusions The dependence of pitch on intensity is associated with defective hearing rather than with any personal bias on the part of the subject. Pitch defects are found with widely different types of deafness, in which recruitment of loudness is present. At low frequencies, as well as at those above 1 cs, threshold defects may be accompanied by pitch defects; at low frequencies pitch changes have been found for apparently normal ears, and it is not yet clear whether detailed examination of the threshold would always reveal a minor defect in such cases. There is no obvious consistent relationship between the degree of recruitment of loudness and the direction of the pitch change at neighbouring frequencies. DSCUSSON These findings confirm that it is abnormal for the pitch of a pure tone to be dependent on intensity, and show that a great many types of irregular audio. gram may be associated with a pitch defect. All the types of deafness which have been examined by the loudness balance method exhibit recruitment of loudness, which is significant of a cochlear lesion. The only thing which these subjects had in common was a unilateral partial deafness, and it would be too much to expect much homogeneity in the results from such a mixed bag. t is rather unusual for a cochlear deafness to affect one ear only, since systemic causes or trauma are rarely confined to one side ofthe head. Hence there is very little chance of choosing subjects with any desired type of deafness in one ear, and good hearing in the other. n forming hypotheses about the mechanisms of pitch-dependence on intensity, it is no longer permissible to assume that the direction in which the pitch moves depends on the presence or absence of recruitment of loudness. t is possible, however, that the loudness of a pure tone draws on the neural response from a greater length of the organ of Corti than goes to determine the pitch, so that detail of the local response along the cochlea might be lost in the loudness results. The idea that a wide area contributes to the loudness of a pure tone is supported by the fact that frequencies flanked by regions of great threshold defect often fail to achieve full recruitment of loudness. Once it is established that the pitch of a pure tone is dependent on intensity for one ear, but not for the other, in the same subject, the next step which seems obvious is to apply the first tone to one ear, and the second tone to the other, and thus to compare the pitch directly. ndeed, exploratory experiments of this kind were made, but met with unexpected difficulties. For some subjects, notably for K.F., there was good agreement with the results obtained from each ear separately. Again, other subjects found no pitch differences between the ears at any intensity. This question clearly demanded a separate investigation, which was not possible at that time, since each subject had

9 PTCH AND RECRUTMENT OF LOUDNESS 363 already spent some ten hours doing the tests, as well as the time spent in travelling. A cause of the difficulty may lie in the fact that the two ears are not completely isolated, a tone applied to one ear by means of an earphone reaching the remote cochlea at an intensity only 5 db below the intensity at which it reaches the nearer cochlea (Sparrevohn, 1946). When the earphone is on the deaf ear, the contribution of the remote ear to the total response must be relatively large. This means that two tones applied in succession to the deaf ear both produce a response from both cochleas at the same time, whereas, if the first tone is applied to the normal ear, and the second to the deaf ear, the comparison must be made between a response from the normal cochlea only, and a response from both cochleas together. n the latter case, the contribution of the defective cochlea might be neglected by some subjects, and the judgement based on successive responses from the normal cochlea. t is known that pitch comparisons by normal subjects are made more accurately when the tones are given in succession to the same ear, than when one tone is presented to one ear, and the second to the other ear (Pikler & Harris, 1955). This suggests that comparison of successive responses from one cochlea may take place in a part of the brain where only one cochlea is represented, while a less efficient comparison may be made between responses from the two cochleas in another part of the brain where both are equally represented. Harris (1948) found that in the method of constant stimuli, the subject makes his comparisons with a subjective reference point, which is a compromise between the objective standard tone and a subjective mid point, near the arithmetic mid point of the range of frequencies of the second tone. n the present tests this tends to reduce the measured size of the pitch changes, but evidently has not suppressed them entirely. When the standard tone is presented to one ear, and the variable second tone to the other, the influence of the psychological mid point may well become stronger and supplant the objective standard tone as a reference point. t is interesting to find that low frequencies are also liable to pitch defects when there are threshold defects nearby. This, of course, requires confirmation from subjects who have both ears the same, though other workers have described many unexplained cases of pitch-dependence on intensity at low frequencies (e.g. Morgan et al. 1951). Although we do not know how the pitch change is induced, there does not seem to be any justification for seeking more than one mechanism for defects which can occur throughout the auditory range.

10 364 PRSCLLA H. STRANGE SUMMARY 1. The influence of intensity on the pitch of a pure tone has been examined, for each ear separately, for six subjects with unilateral deafness. 2. The degree of recruitment of loudness present in the deaf ear of each subject was found by alternate binaural loudness balance, relative to the better ear. 3. The dependence of pitch on intensity was always more marked for the deaf ear than for the better ear, even at frequencies below 1 cs. The pitch defect accompanies many types of irregular audiogram. 4. Each subject showed almost complete recruitment of loudness in the deaf ear, at all frequencies, indicating a cochlear lesion in each case. 5. No obvious connexion was found between the degree of recruitment of loudness and the direction of the pitch change at neighbouring frequencies. 6. Difficulties inherent in any direct comparison of pitch as between the two ears are discussed. am most grateful to the volunteers J.F.C., K.F., J.K., E.N., V.P. and H.C.W. for their co-operation and sustained interest. should also like to thank the authorities of the Audiology Unit of the Royal National Throat, Nose and Ear Hospital for introducing me to some of the subjects, Dr H. J. A. Dartnall for his encouragement and helpful criticism, and Miss Ann Ley for her assistance. REFERENCES FowLER, E. P. (1936). A method for the early detection of otosclerosis. A study of sounds weu above threshold. Tran8. Amer. otol. Soc. 26, HEnis, J. D. (1948). Pitch discrimination and absolute pitch. U.S. Navy Medical Research Laboratory, Bureau of Medicine and Surgery, Progress Report No. 1, Research Project No. NM326. MoRGAw, C. T., GARNER, W. R. & GALA&rBos, R. (1951). Pitch and intensity. J. acou8t. Soc. Amer. 23, PmnLa, A. G. & HARS, J. D. (1955). Channels of reception in pitch discrimination. J. acoust. Soc. Amer. 27, SPA invohn, U. R. (1946). Some audiometric investigations of monaurally deaf persons. Acta oto-laryng., Stockh., 34, 1-1. STRsANG, P. H. (1955). The sense of pitch and local increase in threshold. J. Physiol. 129, STRANGE, P. H. (1956). Pitch-intensity dependence and its relation to the threshold of hearing for high frequencies. J. Phy8iol. 134,