Schlauch Laboratory

Applied and Basic Research: Educating the next generation of Audiologists and Researchers

My name is Bert Schlauch and I am a Professor in the Department of Speech-Language-Hearing Sciences at the University of Minnesota (Twin Cities). My lab addresses a broad range of questions in basic and applied hearing research, but one underlying principle permeates everything I do: I involve students in my research. Many former students - undergraduate and graduate - have published scientific papers with me. Here is a link to those studies.

Below is a summary of some current projects we are working on. Follow the links to learn more and to listen to some sample sounds

 

Research Projects

Improving the precision of audiological behavioral measures:  My students' and my work in this area has improved diagnostic tests for identifying persons with tumors and ones faking a hearing loss.  My current work is refining pure tone threshold measures used to identify persons showing damage from exposure to intense sounds.

Auditory Attention: We seldom listen to sounds in isolation.  The brain does a wonderful job of segregating sounds that we attend to from other, competing sounds.  This work explores the acoustic cues that the brain uses to accomplish this segregation (Click here for more details).

Sounds played backwards: It's an urban legend that if you play one of the Beatles's songs backwards it will reveal a lyric that Paul is dead. Ignoring that hoax, everyone knows that speech or music played backwards has a very different timbre or tone color than sounds played in the normal way.  I quantified some of these effects and discovered that the duration of a common class of sounds played backwards is perceived to be twice as long as the same sound played in the normal fashion.  This finding has implications for composers and for the study of timbre (Listen to the sounds here).

Speech Prosody: Prosody is the feature of speech that describes its melody and rhythm. Most English speakers think of prosody as the feature that enables speakers to convey emotion or, for instance, to signal whether a question is being asked (e.g., a rising pitch at the end of the utterance).  Our studies have found that natural prosody helps listeners understand speech better in background noise (Click Here to Learn More).

Teaching: I routinely offer five different classes. 

Hearing Science (SLHS 3306).  This is an undergraduate class that covers physiological and psychological acoustics. 

Signals and Systems in Audiology (SLHS 8803). This course covers advanced topics in acoustics and calibration of audiometers.  In the image below, some of my students are assessing the calibration of the bone conduction oscillator using an artificial mastoid. 

Audiological Assessment I and II (SLHS 5801 and SLHS 8801):These two semester long courses cover the diagnostic battery.  The first course includes pure tone audiometry, speech measures, and immittance.  The second course covers ABR (including Don's recent advances for tumor identification and diagnosis of Meniere's disease), ASSR, Electrocochleaography, and otoacoustic emissions.  In the image below, a student is practicing masking technique using a computer simulation.  The simulated patient responds to presentations just like a real client.

 

Hearing Science Foundations of Audiology (SLHS 8805): My background in hearing science and audiology give me a unique perspective that enables me to make critical links between hearing science and audiological clinical practice; hearing science is shown to be an important foundation for evaluating clinical protocols.  As part of this class, students create a poster that presents an analysis of current scientific literature.  The posters illustrate links students find between hearing science and Audiology for a narrow topic in an area of their interest. These posters are presented (even and odd numbered posters presented simultaneously during alternate 1/2-hour periods) during the final exam period in a public forum that is attended by other students and faculty.  This group presentation, with multiple posters being presented simultaneously to interested observers, is similar to the format of a national convention (without the stress).     

Flattened Fundamental Frequency

A talker's fundamental frequency (the pitch of their voice) varies continuously in typical speech.  Computer programs now enable modifications to the fundamental frequency which give us a tool to study what  role prosody plays in speech understanding.  Sharon Miller worked on this project while she was earning an MA degree with an emphasis in Audiology.  As part of Sharon's thesis, we examined the ability of listeners to understand key words in sentences in which she had modified the pattern of the voice pitch. The sentences were presented in background noise.  Here are a few examples:

For reference, listen to this normally spoken sentence.

This is an example of monotone or flattened fundamental frequency.

Here is a sentence with variation, but it's unnatural. The fundamental frequency is sinusoidally frequency modulated (FM) with a modulation frequency of 2.5 Hz.

We found that ANYchanges made to the fundamental frequency of a talker's voice made speech understanding in noise worse.  Even though the example with FM modulation sounds more natural (at least to some of us) than the flattened example, speech understanding was poorer in that condition than the flattened one.  That's why we were surprised when we examined the ability of people to understand Tony's speech in noise. Tony, shown below, communicates with an electrolarynx.  In the photo below Tony is using an electrolarynx manufactured by Griffin Laboratories.  His device, unlike most that others that produce monotone speech, has a touch-sensitive button that allows its user to vary the fundamental frequency over time. Tony is shown below with his TruTone electrolarynx.

 

Professor Peter Watson and I recorded Tony producing sentences with his electrolarynx with a varying fundamental frequency and with the same device set to produce a monotone fundamental frequency.  Listeners, under controlled experimental conditions, were able to understand Tony's speech with a varying fundamental frequency better than they were when the fundamental frequency was monotone.

Examples of Tony's speech:

Here is a sample with a monotone fundamental frequency frequency.

Here is a sample with time varying fundamental frequency that Tony produced by pressing the "pitch" button on his device. 

The 12% better speech understanding in noise obtained with the varying fundamental frequency represented a significant improvement. 

A research article describing this work will appear in the American Journal of Speech Language Pathology. The goals of this line of work are to understand the role that prosody plays in speech understanding and to improve the quality of speech production for persons with speech disorders. 

Sounds Played Backwards

The amplitude of many sounds in our environment comes on abruptly and decays gradually over time. The sounds produced when an object is struck produce this kind of sound pattern. Some waveform examples are shown below. These waveforms show amplitude on the vertical axis and time along the horizontal one.

The upper panel shows a strike of a snare drum whereas the lower two panels represent the word "time" spoken by a male talker. In the middle  panel, the word "time" is spoken in a small room whereas the lower panel  has echoes present because it was produced in a large auditorium (simulated). In the auditorium, the sound takes longer to decay due to echoes or reverberation.

Listen to the following tones played frontwards and backwards and judge for yourself which one is longer. The tone played frontwards has the same waveform shape (envelope) as the waveforms above. The backwards one is the same sound simply reversed in time. 

Tone played frontwards.

Tone played backwards.

Even though both tones are the same physical duration (1/10th of a second) the second one with its amplitude coming on slowly and decaying quickly sounds longer.  This same finding holds for more complex sounds such as speech and sounds produced by musical instruments. 

The explanation for the finding likely has a cognitive component.  Persons may ignore the decay of a sound because they perceive it as an echo.  My students and I describe the various hypotheses in our scientific papers on this topic (see papers related to ramped and damped sounds or rising intensity and falling intensity sound in my CV).

Some definitions of timbre describe it as the attribute of a sound that enables a listener to judge one sound as dissimilar from another sound using criteria other than pitch, loudness and duration. Timbre is what enables us to recognize different musical instruments when they play the same note. Our findings suggest that studies of timbre should match sounds for their subjective duration rather than their physical duration. 

Auditory Attention

Chris Plack, my friend in England, describes the problem clearly in his book The Sense of Hearing. Below is a figure from his book that illustrates what our ears do on a daily basis.  In the figure below, Chris is shown being presented simultaneously with the sounds of a car engine, a speaker, and speech. The sound waves add to form a single waveform and in order to hear out the sound we want to attend to, the ear has to segregate the relevant sounds from the combined waveform. 

 

To learn what cues the brain uses to perform this task, we are studying listeners' ability to hear loudness differences for a single tone presented in isolation and in the presence of 8 distracter sounds.  Below is an example of the tone presented in isolation.  It will be presented in pairs, and listeners have to judge whether the first or the second tone in the pair is louder.  The difference in the level of the tone is 4 dB; most people can hear a 1 dB difference so the louder tone in the pair should be discriminated easily.

In the following sequence, you will hear 4 pairs of tones.  Judge whether the first tone in the pair or the second tone in the pair is louder.

Four pairs of tones in isolation.

Answers:

1. First Tone

2. Second Tone

3. First Tone

4. Second Tone

Now listen for that same tone again and try to ignore the eight distracter tones. 

 Four pairs of tones in the presence of simultaneously presented distracter tones.  

That was probably harder.  I will have to check the answers after spectral analysis of the stimuli.  I can't trust my ears on this one or the next one. I'm at near chance performance (50%) on this task.  A study participant with absolute pitch was able to hear out the target tone and had a near perfect score after judging hundreds of pairs. 

This time (below) the distracter tones will be presented but the target tone will be turned on with a roughly 1/3-second delay.  All of the tones are terminated at the same time.  Listeners find this task easier. The delay in the onset of the target tone makes it easier to attend to. I perform near 80% on this task.

Four pairs of tones in the presence of distracters with the onset of the target delayed.

We tend to judge sounds that come on together as originating from a single source.  That's likely why it was harder to segregate the single tone from the distracters in the previous condition.  We are also examining other acoustic cues, such as frequency modulation, that might assist in enabling listeners to hear out the single tone from the distracters.   

Hearing Science at the University of Minnesota

There are many hearing scientists at the University of Minnesota in a variety of departments. Many of us meet on a weekly basis throughout the year to discuss our research and to review current literature in the field, mostly from the Journal of the Acoustical Society of America.  Students are invited  to attend these meetings with us. 

Below is a list of Bert Schlauch's colleagues who study hearing at the University:

Mark Bee

Arlene Carney

Edward Carney

Heather Kreft

Hubert Lim

Robert Margolis

Josh McDermott (Alumnus)

Christophe Micheyl

Ben Munson

David Nelson

Peggy Nelson

Andrew Oxenham

Mark Stellmack

Neal Viemeister

Peter Watson

Magdalena Wojtczak

Yang Zhang

Schlauch CV

Click here for current CV

Publications with Students

           

 

            My former and current students who have published papers in peer-reviewed journals are highlighted in blue below. 

 

            Jahner, J.,Schlauch, R.S., & Doyle, T.  (1994).  “A comparison of American Speech-Language-Hearing Association guidelines for comparing speech recognition thresholds,”  Ear and Hearing l5, 324-329.

 

            Schlauch, R.S., & Morison, L.M.  (1995).  “The spectral spread of loudness adaptation for tones that decrease continu­ously in level,” Acustica 8l, 279-280.

 

            Schlauch, R.S., Harvey, S. & Lanthier, N. (1995). “Intensity resolution and loudness in broadband noise,” Journal of the Acoustical Society of America 98, 1895-1902.

 

            Schlauch, R.S., Levine, S., Li, Y., & Haines, S. (1995). “Evaluat­ing hearing threshold differences between ears as a screen for acoustic neuroma,” Journal of Speech and Hearing Research 38, 1168-1175.

 

            Schlauch, R.S.,Arnce, K.D., Morison, L.M., Sanchez, S., & Doyle, T.N.   (1996). “Identification of pseudohypacusis using speech recognition thresholds,”Ear and Hearing 17, 229-236. (1,3,4,6)

 

            Mineau, S.,& Schlauch, R.S.  (1997). “Threshold measurement in patients with tinnitus: Pulsed or continuous tones,”  American Journal of Audiology 6, 52-56.

 

            Schlauch, R.S., Lanthier, N., & Neve, J. (1997).  “Forward masked intensity discrimination: Duration and spectral effects,”Journal of the Acoustical Society of America 102, 461-467.

 

            Schlauch, R.S., DiGiovanni, J.J., and Ries, D.T. (1998). “Basilar membrane nonlinearity and loudness,” Journal of the Acoustical Society of  America 103, 2010-2020.

 

            Schlauch, R.S., Clement, B.R., Ries, D.T., and DiGiovanni, J.J.(1999). “Masker laterality and cueing in forward-masked intensity discrimination,” Journal of the Acoustical Society of America 105, 822-828.

 

            Ries, D.T., Rickert, M.and Schlauch, R.S. (1999).  “The peaked audiometric configuration in Meniere’s disease: disease related?,” Journal of Speech Language Hearing Research 105, 822-828.

 

            Hunter, L.L., Ries, D.T., Schlauch, R.S., Levine, S.C., and Ward, W.D. (1999). “Safety and clinical performance of acoustic  reflex   tests,” Ear and Hearing 20, 506-514.

Schlauch, R.S., Ries, D.T. and DiGiovanni, J.J. (2001). “Duration discrimination, and subjective duration for ramped and damped sounds,” J. Acoust. Soc. Am. 109, 2880-2887.

 

DiGiovanni, J.J.,Nelson, P. and Schlauch, R. (2005). “A psychophysical evaluation of spectral enhancement,” Journal of Speech, Language, Hearing Research 48, 1121-1135.

 

Opperman, D.A.,Reifman, W., Schlauch, R..S. and Levine, S. (2006). “Incidence of spontaneous hearing threshold shifts during modern concert performances,”  Otololaryngology Head. and Neck Surgery 134, 667-673.

 

DiGiovanni, J.J.and Schlauch, R.S. (2007). “Mechanisms responsible for differences in perceived  duration for rising-intensity and falling-intensity sounds,” Ecological Psychology 19(3), 239-264.

 Ries, D.T., Schlauch, R.S. and DiGiovanni, J. (2008). The role of temporal  masking patterns in the determination of subjective duration and loudness for  ramped and damped sounds. Journal of the Acoustical Society of  America, 124(6):3772-3783. 

Miller, S., Schlauch, R.S., and Watson, P.J. (accepted).  The effects of fundamental frequency contour manipulations on speech intelligibility in background noise. Journal of the Acoustical Society of America.