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Stimulus Characteristics (1)Stimulus FrequencyRange of sensitivity: 20 to 20,000 HzMost sensitive frequency range: approximately 500-5,000 Hz-speech signalsHuman audibility curve

Stimulus Characteristics (2)Stimulus DurationDuration of a stimulus: 10 to about 30 msec.Beyond about 300 msec, sensitivity is not affected by lengthening signal durationPatients with hearing loss: some loss of sensitivity for higher frequencies, particularly 4,000 Hz.Persons with cochlear damages: reduced temporal integrationTemporal integration function: a change in threshold as the duration of a stimulus changes

Frequency: cycles/sec, or Hertz(Hz, from German physicist Heinrich Hertz) Middle C on piano ~ 261.6 Hzhttp://en.wikipedia.org/wiki/Piano_key_frequencies

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Comparative Hearing

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Stimulus Characteristics (3)Stimulus Intensity10 to 100 dB SPLComfortable listening level (approximately 40 dB)Uncomfortable loudness level (approximately 90 dB)A 50 dB range of efficiently usable hearing

Amplitude Range

1010Methods of Stimulus Presentation (1)EarphonesMinimum audible pressure (MAP)Not a natural methodDisadvantages: reduced natural amplification provided by the resonance of the outer ear, eliminating the slight increase in sensitivity, eliminating the effects of a reverberant acoustic environment.Advantages: the increased ease of control of stimuli, isolation of ears, and reduction of ambient noise

Methods of Stimulus Presentation (2)SpeakersSound field testingMinimum audible field (MAF): more sensitive than MAP by 6 to 10 dBSeveral other contributing acoustic effects:Reverberation: incident sound-the sound coming directly from a speaker, reflected sound. Incident and reflected sound can interactHead shadow: a reduction of sound level at the ear on the far side of the sound sourceBoby baffle: the acoustic effect of the bodys presence in the sound field

Assessment of Auditory Sensitivity (1)Method of LimitsChanging one parameter of the auditory stimulus (intensity)Descending approach: decreasing intensity between presentations until it is inaudibleAscending approach: increasing intensity between presentations until it is audibleDescending approach is 3 to 4 dB more sensitive than ascending approach

Assessment of Auditory Sensitivity (2)Method of AdjustmentHaving the subject adjust some parameters (intensity) to a point where it is barely audible.Tracking threshold

Assessment of Auditory Sensitivity (3)Method of Constant StimuliTwo-alternative forced-choice procedurePercentage of time each level of stimulus was detectedThreshold: 50% response level

Assessment of Auditory Sensitivity (4)Listener (Subject) VariablesSubject: determine whether a stimulus is heard or notThe direction given by the examinerFalse-positive response: an individual responds frequently when no stimulus is being presented

Assessment of Auditory Sensitivity (5)Age VariablesPresbycusis: age-related hearing lossSocioacusis: hearing loss usually associated with the aging processHow is Noise-induced hearing loss related?

What is Normal Hearing?AudiogramGraph or table showing thresholds in hearing level at different frequenciesDegree of hearing loss (0-110 dB)Frequency information (250-8,000 Hz)Types of hearing loss (Air conduction or bone conduction)

Localization of Sound (1)Intensity CuesThe near side and the far sideHead shadow effectAzimuth: angle of incidence of a sound wave as it reaches the head. A zero-degree azimuth indicates that the sound is directly in front of the head.

Localization of Sound (2)Time Cues for LocalizationInteraural time differencesMinimum audible angle: smallest separation of angles of incidence that can be perceivedTime cues serving as the important cues for the localization of lower frequenciesIntensity cues serving the localization of higher frequencies

Hearing by Bone ConductionBone conductionTransmission of sound waves to the inner ear through vibration of the bones of the skullThree different modesInertial bone conduction: result from the initial of the ossicular chainCompressional bone conduction: results from segmental vibration of the bones of the skullOsseotympanic bone conduction: results from the production of air conducted sound in the external auditory canal by the vibration of the bony walls of the canalOcclusion effect: production and enhancement of air-conducted sound in a plugged external auditory canal that was originally created by the vibration of the bony walls of the canal