Patent Application: US-201615044743-A

Abstract:
the application relates to a method for recording auditory steady - state responses responses of a person , the method comprising a ) providing an acoustic stimulus signal to an ear of the person , b ) recording the auditory steady - state responses of the person originating from said acoustic stimulus signal . the application further relates to a system . the object of the present application is to excite the auditory system with a signal capable of assessing the auditory systems ability to process speech . the problem is solved in that the acoustic stimulus signal comprises a speech - like stimulus provided as a combination of a series of frequency - specific stimuli , each having a specified frequency bandwidth , presentation rate , amplitude and amplitude - modulation . an advantage of the disclosure is that it allows a clinical assessment of the effect of a hearing device in a normal mode of operation , i . e . when processing speech stimuli . the invention may e . g . be used for diagnostic instruments for verifying the fitting of a hearing aid .

Description:
the detailed description set forth below in connection with the appended drawings is intended as a description of various configurations . the detailed description includes specific details for the purpose of providing a thorough understanding of various concepts . however , it will be apparent to those skilled in the art that these concepts may be practiced without these specific details . several aspects of the apparatus and methods are described by various blocks , functional units , modules , components , circuits , steps , processes , algorithms , etc . ( collectively referred to as “ elements ”). depending upon particular application , design constraints or other reasons , these elements may be implemented using electronic hardware , computer program , or any combination thereof . the electronic hardware may include microprocessors , microcontrollers , digital signal processors ( dsps ), field programmable gate arrays ( fpgas ), programmable logic devices ( plds ), gated logic , discrete hardware circuits , and other suitable hardware configured to perform the various functionality described throughout this disclosure . computer program shall be construed broadly to mean instructions , instruction sets , code , code segments , program code , programs , subprograms , software modules , applications , software applications , software packages , routines , subroutines , objects , executables , threads of execution , procedures , functions , etc ., whether referred to as software , firmware , middleware , microcode , hardware description language , or otherwise . fig1 a shows an embodiment of a method of generating a speech - like stimulus signal . fig1 b shows an embodiment of diagnostic system for recording an auditory evoked potential according to the present disclosure . fig1 a shows the principle and preferred embodiment of the stimulus generation of the present disclosure . to the left ( block octave - band chirps ), as an example , four octave - band chirps are generated with the centre frequencies of 500 , 1000 , 2000 , and 4000 hz . the stimuli are presented at different rates of stimulation ( see e . g . fig2 a , 2b , 2c , 2d ) and can be used for the simultaneous multiple frequency - specific stimulation of the assr ( cf . e . g . wo2006003172a1 , [ elberling et al ., 2007b ]). the four chirps are next ( cf . block spectral shaping ) spectrally shaped so the amplitude spectrum of the combined signal corresponds to the long - term spectrum of running speech spoken with a specific vocal effort ( here as an example the vocal effort is ‘ normal ’— ansi s3 . 5 . ( 1997 )). next ( cf . blocks modulation ), the combined and spectrally shaped signal is fed into an amplitude modulator , which modulates either each of the band - limited stimuli or the combined broad - band signal with a real or simulated envelope of running speech ( cf . e . g . [ plomp , 1984 ]). finally ( cf . stage simulated speech signal ) the simulated speech signal is fed to a stimulus transducer ( here a loudspeaker is shown as an example ) with a presentation level as required . in fig1 a references are made to the detailed temporal waveforms in fig2 a - 2g . fig1 a schematically illustrates an embodiment of a stimulation part ( represented by stu and ot in fig1 b ) of a diagnostic system . fig1 b schematically shows an embodiment of a diagnostic system ( dms ) comprising a stimulation unit ( stu ), an output transducer ( ot ), and a recording unit ( rec ) in communication with a number of recording electrodes ( rec - el ). fig1 b further includes a user ( u ) wearing a hearing device ( hd ) at a 1 st ear ( 1 st ear ) and an ear plug ( plug ) at the 2 nd ear ( 2 nd ear ). fig1 b illustrates ‘ free field ’, aided measurement with a diagnostic system according to the present disclosure . the hearing device is adapted for picking up sound from the environment to provide an electric input signal , and comprises a signal processing unit for providing an improved signal by applying a level and frequency dependent gain to the input signal to compensate for a hearing impairment of the user &# 39 ; s 1 st ear , and an output unit for presenting the improved signal as output stimuli perceivable by the user as sound . the ear plug ( plug ) is adapted to block sound at the 2 nd ear from evoking neurons in the auditory system . when electric stimuli ( stim ) generated by the stimulation unit ( stu ) and converted to acoustic stimuli ( ac - stim ) via output transducer ( ot ), the acoustic stimuli ( ac - stim ) are picked up by the input transducer of the hearing device ( hd ) at the first ear ( 1 st ear ) of the user ( u ), processed by the signal processing unit , and presented to the auditory system ( auditory system ) of the user via the output unit of the hearing device . the stimuli from the output unit of the hearing device evokes responses ( aep ) from the auditory system ( auditory system ). the evoked responses ( aep ) are recorded by the recording unit ( rec ) via recording electrodes ( rec - el ) mounted on the user &# 39 ; s head ( head ), e . g . attached to the skin and / or tissue of the user &# 39 ; s scalp or ear canal . the recording ( rec ) and stimulation ( stu ) units are in communication ( cf . signal cont ), e . g . to control timing relations between the generation of stimuli by the stimulation unit and the detection and processing of evoked responses ( assrs ) by the recording unit . fig2 a , 2b , 2c , 2d , 2e , 2f shows exemplary individual signal components from which a resulting speech - like stimulus signal ( as illustrated in fig2 g ) is generated . fig2 a - 2g shows the details of the time signals at the different stages of the proposed invention . from top to bottom : first the four frequency - specific stimuli are shown using a time scale of 100 ms ( fig2 a - 2d ). the different rates of stimulation are indicated to the left and as an example vary from 84 . 0 / s to 90 . 6 / s . fig2 a shows a 500 hz narrow band chirp with a stimulation rate ( repetition rate ) of 86 . 0 hz . fig2 b shows a 1000 hz narrow band chirp with a stimulation rate of 90 . 6 hz . fig2 c shows a 2000 hz narrow band chirp with a stimulation rate of 84 . 0 hz . fig2 d shows a 4000 hz narrow band chirp with a stimulation rate of 88 . 6 hz . each of the narrow band chirps is generated by respective filtering ( with a 1 octave bandpass filter ) of a broadband linear chirp between a minimum frequency ( e . g . 350 hz ) and a maximum frequency ( e . g . 11 . 3 khz ) ( cf . [ elberling & amp ; don , 2010 ]). the spectrally shaped combined broad - band signal is shown in fig2 e as the ‘ sum of weighted chirp signals ’. in fig2 a - 2g , four frequency - specific stimuli , each comprising a periodically repeated ( 1 octave wide ) narrow band chirp , are used to generate the combined broad - band signal . alternatively , another number of narrow band chirps may be used , e . g . 12 ( ⅓ octave wide ) narrow band chirps covering the same frequency range from appr . 350 hz to appr . 5600 hz . next , using a time scale of 10 s , an example of a ‘ simulated speech envelope ’ is shown in fig2 f , and finally the corresponding modulated output signal is shown as the ‘ simulated speech signal ’ in fig2 g . the simulated speech envelope in fig2 e is e . g . generated as an envelope of exemplary free - running speech . fig3 shows an example of the iec60118 - 15 , ( 2012 ) method for determining hearing aid insertion gain and appropriate level dynamic range for speech - like stimuli . fig3 gives an example of the iec60118 - 15 , ( 2012 ) method for determining hearing aid insertion gain and appropriate level dynamic range ([ db spl ] versus frequency [ hz ]) for speech - like stimuli . on the left figure ( denoted unaided ) is shown the level variations of a standardized speech test - stimulus ([ holube et al ., 2010 ]) recorded in a hearing aid test - box ( interacoustics tb25 ). the level variation for each ⅓ - octave band is indicated by the 30 , 65 and 99 th percentiles of the corresponding distribution of the short - term ( 125 ms ) amplitude values . also shown is the long term amplitude speech spectrum ( ltass ) in one - third octave bands . the middle figure ( denoted aided ) shows the output from a paediatric hearing aid , measured in the test - box using an occluded - ear simulator ( iec 60318 - 4 , 2010 ). on the right figure ( denoted eig = aided - unaided @ 65 db spl ) is shown the estimated insertion gain ( eig ). it is observed that the estimated insertion gain of signal components having relatively lower input levels ( represented by the 30 % percentile ) is larger than the estimated insertion gain of signal components having relatively higher input levels ( represented by the 99 % percentile ). this is e . g . due to a compression algorithms , which tend to amplify low input levels more than high input levels . a preferred embodiment of the present invention is to use the methods set down in the iec 60118 - 15 , ( 2012 )- standard to demonstrate the speech - like processing of the new assr stimuli with digital hearing aids . fig4 a and 4b shows exemplary setups of a diagnostic system for verifying a fitting of a hearing aid , fig4 a and 4b illustrating an aep measurement , where the user wears a hearing device in a normal mode ( aided ), and where the user does not wear a hearing device ( unaided ), respectively . the diagnostic system comprises the components discussed in connection with fig1 b and is in fig4 a used in an aided measurement where free field acoustic stimuli ( ac - stim1 ) from the output transducer ( ot , here a loudspeaker ) are picked up by a hearing device ( hd1 ) adapted for being located in or at a first ear ( ear1 ) of a user ( u ) ( or fully or partially implanted in the head of the user ). the hearing device comprises an input unit ( iu , here a microphone is shown ), a signal processing unit ( not shown ) for applying a level and frequency dependent gain to an input signal from the input unit and presented such enhanced signal to an output unit ( ou , here an output transducer ( loudspeaker ) is shown ). the output transducer of the hearing device is in general configured to present a stimulus ( based on the signal picked up by the input unit iu ), which is perceived by the user as sound . the auditory system of the user is schematically represented in fig4 a and 4b by the ear drum and middle ear ( m - ear ), cochlea ( cochlea ) and the cochlear nerve ( neurons ). the nerve connections from the respective cochlear nerves to the auditory centre of the brain ( the primary auditory cortex , denoted pac in fig4 a and 4b ) are indicated by the bold dashed curves in fig4 a and 4b . the diagnostic system comprises a stimulation unit ( stu ) adapted to provide an electric stimulus signal ( stim1 ) comprising a number of individually repeated frequency specific stimuli , which are combined and spectrally shaped in amplitude to emulate a long - term spectrum of running speech ( at a certain vocal effort ), and amplitude modulated in time to provide an envelope of the stimuli equivalent to that of running speech . the diagnostic system further comprises a recording unit ( rec ) for recording the auditory evoked responses of the person originating from said acoustic stimulus signal ac - stim1 . in the scenario of fig4 b the free field acoustic stimulus signal ac - stim1 is received by the persons &# 39 ; ear and auditory system ( without hearing aid means , i . e . in an ‘ unaided ’ mode ). in the scenario of fig4 a the free field acoustic stimulus signal ac - stim1 is picked up , processed and presented to the person &# 39 ; s auditory system by the hearing device ( i . e . an ‘ aided ’ mode ). in both the aided and unaided setup , the stimulation is provided at one ear ( the right ear , ear1 ) and the other ear ( the left ear , ear2 ) is provided with an ear plug ( plug ) to block sound that ear from evoking neurons in the auditory system . the recording unit comprises or is operationally connected to electrodes ( acq ) adapted to pick up brainwave signals ( rec0 , rec1 , rec2 ) ( e . g . aeps ) when appropriately located on the head of the user . in the embodiments of fig4 a and 4b , three electrodes ( acq ) are shown located on the scalp of the user ( u ). the recording unit and the stimulation unit are in communication with each other ( signal cont ), e . g . to control a timing between stimulation and recording . the recording unit comprises appropriate amplification , processing , and detection circuitry allowing specific assr data to be provided . fig5 a shows an embodiment of a diagnostic system alone , and fig5 b shows an embodiment of a diagnostic system stimulating a hearing device while worn by a person . fig5 a is a block diagram of a diagnostic system ( dms ) as also illustrated and described in connection with fig4 a and 4b and in fig1 b . the diagnostic system comprises an electrode part ( acq ) comprising a number n e of electrodes for picking up evoked potentials rec n from the auditory system and brain when mounted on the head of the user . the evoked potentials rec n picked up by the electrodes are fed to the recording unit ( rec ) for processing and evaluation . electric stimuli stim ( e . g . controlled ( e . g . initiated ) by the recording unit ( rec ) via control signal cont ) according to the present disclosure are generated by the stimulation unit ( stim ) and converted to ( free field ) acoustic stimuli ac - stim by an output transducer ( loudspeaker ) of the system . fig5 b shows the diagnostic system ( dms ) used in an ‘ aided ’ mode ( as illustrated and discussed in connection with fig4 a ), where a person wearing a hearing device ( hd ) is exposed to the acoustic stimuli ( ac - stim ) of the diagnostic system at one ear . the acoustic stimuli ( ac - stim ) are picked up by a sound input ( sound - in ) of the hearing device located at the ear . the acoustic stimuli ( ac - stim ) are converted to an electric input signal by a microphone of the hearing device and processed in a forward signal path of the hearing device to a loudspeaker presenting the processed stimuli the user as an output sound ( sound - out ). the forward path of the hearing device ( hd ) comprises e . g . an analogue to digital converter ( ad ) providing a digitized electric input signal ( in ), a signal processing unit ( spu ) for processing the digitized electric input , e . g . in a speech processing mode of operation , and providing a processed signal ( out ), which is converted to an analogue signal by a digital to analogue converter ( da ) before it is converted to sound signal by the loudspeaker of the hearing device . the output sound ( sound - out ) from the hearing device represents a processed version of the speech - like acoustic stimuli ( ac - stim ) from the diagnostic system ( as delivered by the hearing device ). the user &# 39 ; s auditory system picks up the output sound ( sound - out ) from the hearing device ( hd ) and evokes potentials ( aep ) that are picked up by the electrodes ( acq ) of the diagnostic system ( dms ). the diagnostic system ( dms ) and the hearing device ( hd ) together represent a combined system ( cs ). the hearing device ( hd ) can be of any kind ( type ( air conduction , bone conduction , cochlear implant ( or combinations thereof ), style ( behind the ear , in the ear , etc .) or manufacture ) capable of enhancing a speech ( or speech - like ) input signal according to a user &# 39 ; s needs . in an embodiment , the capability of the hearing device to process speech - like stimuli signals from the diagnostic system as ordinary speech is verified in a separate measurement ( e . g . in a low - reflection measurement box ), e . g . according to the iec 60118 - 15 ( 2012 )- standard , cf . further below . as an example , the assr stimulus according to the present disclosure may be generated by four one - octave wide narrow - band ( nb ) chirp - train assr stimuli — constructed according to the methods described in u . s . pat . no . 8 , 591 , 433 b2 , and with centre frequencies 500 , 1000 , 2000 , and 4000 hz and repetition rates 86 . 0 / s , 90 . 6 / s , 84 . 0 / s , and 88 . 6 / s respectively . these examples are illustrated in fig2 ( a - d ). to make the stimulus speech - like , the target sound pressure level should preferably correspond to normal speech levels in the octave bands . the stimulus should preferably be presented in a room with only minor reflections ( e . g . anechoic ). each band is then weighted according to ansi s3 . 5 . ( 1997 ) for normal vocal effort speech measured at a distance of 1 m from the source ( e . g . a loudspeaker ). according to the ansi - standard the octave - band sound pressure levels are then set to 59 . 8 , 53 . 5 , 48 . 8 and 43 . 9 db spl for the 500 , 1000 , 2000 and 4000 hz octave bands respectively . the bands are then combined ( see fig2 e ), such that the sum of the individual bands will result in a broad - band stimulus with a long - term spectrum identical to speech at normal vocal effort , corresponding to a free - field sound pressure level of approximately 62 . 5 db spl . next the broad - band stimulus is fed to a modulator and the simulated speech envelope is applied . this is illustrated in fig2 f as a low - pass ( 4 hz cut - off ) filtered envelope of gaussian white noise . the modulator multiplies the broad - band assr stimulus with the simulated speech envelope and the result is shown in fig2 g . when presented through a hearing aid , the co - modulation of envelope power across bands and the fluctuation in band power will in principle excite the device in a mode of operation similar to speech . by using the iec 60118 - 15 ( 2012 )- standard , the appropriate acoustic measurements in a hearing aid analyser can be made to demonstrate that the stimulus is processed by the hearing aid in a manner similar to speech . normal speech has inherent level fluctuations ( amplitude modulation ), the dynamic range of these over time in the free - field is an important characteristic for speech , and are analysed in ⅓ - octave bands in the iec60118 - 15 standard . if the new assr stimulus has the same input dynamic range as a standardised speech stimulus it is ensured that the hearing aid is stimulated correctly . the output from the hearing aid and the estimated insertion gain are also made to quantify this relationship and further demonstrate that the hearing aid is processing the stimulus in a speech - like manner . an example of this procedure is given in fig3 . in the present example the am is applied to the combined broad - band stimulus ( cf . fig2 a - 2g ). alternatively , the am can be applied in a way as to simulate the co - modulation in normal speech , i . e . have narrow band regions with common modulation rather than across the full region of the broad - band stimulus . this could simply be done using a filter - bank and multiple - modulators before combining into a single broad - band stimulus . this is illustrated in fig6 . fig6 shows an embodiment of a stimulation unit ( stu ) according to the present disclosure . the stimulation unit ( stu ) of fig6 comprises a generator of frequency specific stimuli ( fssg ), e . g . narrowband stimuli as shown in fig1 a , 1b , 2a - 2g , but alternatively other frequency specific stimuli , e . g . stimuli generated by individual pure tones each tone amplitude modulated by a lower frequency carrier . the frequency specific stimuli generator ( fssg ) provides stimuli signals fs - stim . the stimulation unit ( stu ) further comprises a spectrum shaping unit ( ssu ) that shapes the frequency specific stimuli fs - stim to provide that the amplitude spectrum of the resulting combined signal ss - stim corresponds to the long - term spectrum of running speech , e . g . spoken with a specific vocal effort . the stimulation unit ( stu ) further comprises an analysis filter - bank ( a - fb ) that splits the frequency shaped stimuli ss - stim in a number n of frequency bands , providing ( time - varying ) frequency shaped band signals shst1 , shst2 , shstn . the stimulation unit ( stu ) further comprises band - level modulators ( denoted ‘ x ’ in fig6 ) for amplitude modulating frequency shaped band signals shst1 , shst2 , shstn with individual band level modulation functions rsam1 , rsam2 , rsamn , provided by a band level modulation unit ( blm ) configured to provide that the resulting amplitude modulated frequency shaped band signals smst1 , smst2 , smstn have an envelope equivalent to that of running speech . the stimulation unit ( stu ) further comprises a combination unit ( here in the form of a sum unit ) to combine band level signals smst1 , smst2 , smstn to provide a resulting time - domain stimulation signal stim . the resulting electric stimuli stim may then be converted to acoustic stimuli ( cf . ac - stim in fig1 b , 4 and 5 ) by an electro - acoustic transducer ( cf . e . g . ot in fig1 b ), e . g . a loudspeaker ( cf . e . g . speaker in fig1 a , 4 , 5 ). fig7 a , 7b , and 7c shows scenarios similar to those of fig4 a described above . a difference , though , is that the stimuli generated by the stimulation unit ( stu ) of the diagnostic system in the embodiments of fig4 a are transmitted ( wired or wirelessly ) directly to the hearing device ( s ) or are generated in the hearing device ( s ) ( instead of being played via a loudspeaker of the diagnostic system and picked up by the microphone ( s ) of the hearing device ( s )). in both cases , the stimuli are presented to the user ( u ) via a loudspeaker ( ot ) of the hearing device ( hd1 ). fig7 a shows a first scenario of an aep measurement , where the user ( u ) wears a hearing device ( hd1 ) in a normal mode ( aided ), and where stimuli stim1 are provided by a stimulation unit ( stu ) of the diagnostic system directly to the hearing device ( hd1 ) for being played to the ( u ) user by a loudspeaker ( ot ) of the hearing device ( hd1 ). the connection between the diagnostic system and the hearing device may be a wired connection of a wireless connection ( e . g . based on bluetooth or other standardized or proprietary technology ). fig7 b shows a second scenario of an aep measurement , where the user ( u ) wears a hearing device ( hd1 ) in a normal mode ( aided ), and where stimuli stim1 are provided directly ( electrically ) to the hearing device for being played to the user by a loudspeaker of the hearing device . the embodiment of fig7 b is similar to the embodiment of fig7 a . a difference is though that the stimuli generated by the stimulation unit ( stu ) of the diagnostic system in fig7 a are generated in the hearing device ( hd1 ) instead . the stimulation unit ( stu ) is located in the hearing device ( hd1 ) and controlled by the diagnostic system via control signal cont ( here ) from the recording unit ( rec ) of the diagnostic system . fig7 c shows a third scenario of an aep measurement . the embodiment of fig7 c is similar to the embodiment of fig7 b . a difference is that in the embodiment of fig7 c , the user wears first and second hearing devices ( hd1 , hd2 ) of a binaural hearing system in a normal mode ( aided ) ( instead of a single hearing device at one of the ears ). both hearing devices ( hd1 , hd2 ) comprise a stimulation unit ( stu ), which is controlled by the diagnostic system via control signal cont ( here ) from the recording unit ( rec ) of the diagnostic system . an advantage of the embodiments of fig7 a , 7b and 7c compared to the embodiment of fig4 a is that the stimuli are provided electrically to the loudspeaker of the hearing device ( not via intermediate electric to acoustic transducer ( loudspeaker of diagnostic system ) and acoustic to electric transducer ( microphone of hearing device )). fig8 shows an embodiment of a combined system ( cs ) comprising a diagnostic system ( dms ) stimulating a hearing device ( hd ) while worn by a person ( u ), wherein stimulation stim is transmitted directly to the hearing device ( hd ) and provided via a loudspeaker ( ot ) of the hearing device ( hd ). the embodiment of fig8 is similar to the embodiment of fig5 b . the forward path of the hearing device ( hd ) comprises an input transducer ( here a microphone ), an analogue to digital converter ( ad ), signal processing unit ( spu ), a combination unit ( cu ), a digital to analogue converter ( da ), and an output transducer ( here a loudspeaker ). a difference to the embodiment of fig5 b is that in the embodiment of fig8 , the stimulation signal stim is sent directly from a stimulation unit ( stim ) of the diagnostic system ( dms ) to a combination unit ( cu ) the hearing device ( hd ) via an interface ( if ), ( e . g . a wireless interface ). the combination unit ( cu ) is configured to allow a stimulation signal stim received from the diagnostic system ( dms ) to be presented to a user ( u ) via the loudspeaker ( and da - converter ( da )) of the hearing device ( either alone or in combination ( mixed with ) the processed signal ps from the signal processing unit ( spu ) of the forward path of the hearing device ( hd ). the combination unit may be controlled by the diagnostic system ( e . g . by a signal transmitted via the ( e . g . wireless ) interface ( if )). it is intended that the structural features of the devices described above , either in the detailed description and / or in the claims , may be combined with steps of the method , when appropriately substituted by a corresponding process . as used , the singular forms “ a ,” “ an ,” and “ the ” are intended to include the plural forms as well ( i . e . to have the meaning “ at least one ”), unless expressly stated otherwise . it will be further understood that the terms “ includes ,” “ comprises ,” “ including ,” and / or “ comprising ,” when used in this specification , specify the presence of stated features , integers , steps , operations , elements , and / or components , but do not preclude the presence or addition of one or more other features , integers , steps , operations , elements , components , and / or groups thereof . it will also be understood that when an element is referred to as being “ connected ” or “ coupled ” to another element , it can be directly connected or coupled to the other element but an intervening elements may also be present , unless expressly stated otherwise . furthermore , “ connected ” or “ coupled ” as used herein may include wirelessly connected or coupled . as used herein , the term “ and / or ” includes any and all combinations of one or more of the associated listed items . the steps of any disclosed method is not limited to the exact order stated herein , unless expressly stated otherwise . it should be appreciated that reference throughout this specification to “ one embodiment ” or “ an embodiment ” or “ an aspect ” or features included as “ may ” means that a particular feature , structure or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure . furthermore , the particular features , structures or characteristics may be combined as suitable in one or more embodiments of the disclosure . the previous description is provided to enable any person skilled in the art to practice the various aspects described herein . various modifications to these aspects will be readily apparent to those skilled in the art , and the generic principles defined herein may be applied to other aspects . the claims are not intended to be limited to the aspects shown herein , but is to be accorded the full scope consistent with the language of the claims , wherein reference to an element in the singular is not intended to mean “ one and only one ” unless specifically so stated , but rather “ one or more .” unless specifically stated otherwise , the term “ some ” refers to one or more . accordingly , the scope should be judged in terms of the claims that follow . ansi s3 . 5 . 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( 1987 ), ‘ potentials evoked by the sinusoidal modulation of the amplitude or frequency of a tone ’, j . acoust . soc . am ., 82 ( 1 ), 165 - 178 . [ plomp ; 1984 ] plomp , r . ( 1984 ), ‘ perception of speech as a modulated signal ’, in proc . of the 10 th int . cong . of phon . sci ., eds . van der broecke and cohen , 29 - 40 .