Much of the hospital's success in identifying and treating children with hearing loss is the result of the rapid transfer of research findings from laboratories to clinic and bedside.

Areas of Research - Clinical and Behavioral Studies of Human Communication - Psychoacoustics

Overview

The goal of research in this laboratory is to understand the rules governing detection and discrimination of simple sounds by human listeners and to use that information to refine models of how the ear processes sounds.  These models have applications in audiology, hearing aid fitting, and speech perception and play a role in MP3 algorithms used to compress the length of digital music files.  Much of our understanding of how the ear works comes from detailed studies of how one sound interferes with detection of another sound.  For interference or masking to occur, the two sounds must be close together in both frequency and time.  In listeners with normal hearing, masking does not change linearly with sound level, so results obtained with low-level sounds cannot be generalized to high-level sounds.  One of our goals is to understand and correctly model those nonlinear effects.   All models of detection and discrimination are based on judgments or decisions made by subjects in psychoacoustics experiments.  Our second goal is to understand the rules governing those decisions and the limitations in the decision process.  Detection and discrimination can be based on differences in overall energy or on recognition of patterns in time or in frequency.   By relating the subjects’ individual responses to properties of individual stimuli, we can determine the specific features of stimuli that govern the responses.  Our third goal is to relate masking data obtained with behavioral techniques to masking data obtained in studies of otoacoustic emissions.  This work, being done in collaboration with BTNRH research programs that focus on otoacoustic emissions, will provide additional information concerning the relative contributions of cochlear mechanics and decision processes to results obtained with behavioral measures.

Facilities

The laboratory is equipped with two double-walled, sound-treated booths.  The main booth is subdivided into four cubicles for simultaneous testing of four subjects.  Each cubicle is controlled by a separate PC equipped with a 24-bit Card Delux sound card.  Stimuli are presented through Sennheiser 250 headphones and responses are obtained using keypads controlled through a serial interface or through a keyboard and mouse.  The second booth has a PC with a 24-bit soundcard and an Etymotic ER-10C low-noise microphone system that is used for the measurement of otoacoustic emissions. 

Staff

The laboratory is directed by Walt Jesteadt, Ph.D.   Stephen T. Neely, D.Sc. works closely with Dr. Jesteadt and other members of the laboratory staff on models of auditory perception.  Donna L. Neff, Ph.D. is a frequent collaborator on studies involving stimulus uncertainty and informational masking.  Harry Patra, Ph.D. is currently working in the laboratory as a postdoctoral fellow. Hongyang Tan, M.S. is a programmer who implements computer models of detection and discrimination, develops special-purpose data analysis software, and aids other members of the laboratory staff with data analysis.  Jessica Messersmith, Ph.D., a student in audiology at the University of Nebraska, and Melissa Krivohlavek are currently working in the laboratory as research assistants.

Summary of Research Program

Clinicians and Scientists / Families

For Clinicians and Scientists

The current focus of this research program is to develop a better understanding of fundamental aspects of human hearing by characterizing differences in decision processes for three tasks that use the same basic stimuli in different temporal configurations: intensity discrimination, increment detection, and forward masking.  The classic and ubiquitous energy detector model of the decision process provides a good account of data for intensity discrimination.  An alternative to energy detection, however, is required to account for results obtained in increment detection and forward masking, as well as the majority of other detection and discrimination tasks.  Alternative models of the decision process, in particular “template matching”, are currently poorly defined and make vague predictions.  We are seeking to characterize properties of the decision process in these tasks by determining the effects of variability in overall stimulus level and the effects of introducing background noise.  Performance measures include adaptive thresholds, psychometric functions, direct measures of internal noise, and the correlation of specific features of stimuli with each subject’s response on individual trials.  The specific aims are: 1) to determine the relation between peripheral nonlinearity and the slopes of psychometric functions; 2) to compare decision processes in intensity discrimination and increment detection; 3) to determine the effects of noise on intensity discrimination, increment detection and forward masking; and 4) to develop and compare direct measures of internal noise.  This goal is to arrive at a better characterization of alternative decision processes, a detailed test of specific features of the decision process associated with each of the three basic psychophysical tasks considered here, measures of internal noise appropriate to each task, and a better understanding of the interaction of peripheral compression and internal noise in multi-stage models of masking.  

In addition to the work on decision processes in detection and discrimination, we are also involved in collaborative efforts to relate masking data obtained with behavioral techniques to masking data obtained in studies of otoacoustic emissions. 

Families

Research in psychoacoustics is concerned with the relation between the physical properties of sound, such as frequency and intensity, and the psychological or perceptual properties, such as pitch and loudness.  Physical properties of sound can be readily assessed, but measuring the sensory or perceptual experience evoked by a sound is more difficult.  Audiologists are required to make such measurements every day, establishing when sounds can be heard, for example, or how loud they are.  Our research program is focused on the problem of using the physical properties of sounds to predict how well one sound will interfere with or mask the perception of another.  Interference or masking can have negative or positive properties.  Noise, for example, can interfere with perception of speech sounds or with detection of warning signals.  In other situations, noise is introduced to mask sounds that listeners would find annoying or distracting.  Data obtained in many masking studies can be explained in terms of the mechanical properties of the inner ear and we know that cochlear hearing loss results in differences in masking data.  We would therefore like to turn the problem around and use masking data to tell us more about how the inner ear works in individual subjects or in patients with hearing loss.  Data obtained in any hearing test, however, are also influenced by the brain and it is important to separate these cognitive effects from what is going on in the ear itself.  We are particularly concerned with developing better measures of what details subjects listen to when making difficult sound discriminations and the strategies that they use to make their decisions.  Another area of research in the laboratory is concerned with how results obtained using otoacoustic emissions are related to results obtained in our studies of detection and discrimination.  One of the goals of research with otoacoustic emissions is for clinicians to be able to use these mechanical responses of the ear to determine what infants hear.  That will require us to understand how emissions relate to perception.  Because the brain plays less of a role in determining the magnitude of emissions, this area of research also helps us understand more about the contribution of cognitive effects to the perceptual data.

Professional Resources:  There won't be any for my lab.

Specific Areas of Research:

1. Decision processes in auditory detection and discrimination
2. Multistage functional models of detection and discrimination
3. Relation between behavioral and OAE measures of response growth and masking
4. Relation between variability in SFOAEs and the limits of intensity discrimination