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Chapter 3 – Psychoacoustics Psychoacoustics and Audiology Psychoacoustics- studying the ____________ process to learn about the ___________ mechanisms (clinical audiology studies an individual’s hearing which is an application of psychoacoustics) The Concept of a Sensory Threshold Sensations and perceptions of an individual cannot be measured directly, must be observed from ___________. Most common audiometric procedure is measuring a detection _________ (see figure 3.1) o Here, the strength of a signal is gradually raised from a point where it is not detectable to a point where it is clearly ___________. o This is called a _________ __________ and is illustrated in figure 3.1 by the abrupt change; it has an infinitely __________ slope Real life data from __________ testing suggests this isn’t how it works for listeners More accurate depiction is shown by the dashed line in 3.1 o Sounds are detected over a range of ______________ o As intensity __________, the probability of the sound being heard increases o It is not apparent which intensity should be called threshold, rather, it illustrates that varying intensity changes the probability of __________ Since detection is a ____________ process, thresholds are subject to __________ o Cause of variability? Process of detection is actually quite complex: Conversion from ____________ to mechanical energy within the middle ear Transduction of mechanical energy to neural ____________ in the cochlea The propagation of the stimulus through the ________ The perceptual and __________ processes that ultimately determine whether the sound is “heard” The _________ circuitry associated with responding to indicate that the sound was heard Internal noise of the listener (see figure 3.2) We assume internal noise to be Gaussian and always present How Do We Measure What We Hear A discussion of methods used to measure detection thresholds and just noticeable differences “JNDs” Distinction between “classical” and “modern” has to do with the emergence of ___________ detection theory and the procedures that followed from this theory 3 “classical” psychophysical methods: o Method of Limits Most common method used for measuring ___________ in clinic Up-down approach much like the ____________________ method (chapter 5) o Method of Adjustment Quick, simple, straightforward Listener has control of the ___________ level and adjusts the value until it meets a criterion set by the tester A tester may instruct the listener to vary the level of a tone until it can barely be _____________ or until it can no longer be __________ Dependent on the tester’s ___________ and the listener’s ___________ Very subjective o Method of Constant Stimuli (see figure 3.3) A set number of stimulus levels are presented _____________, a set number of times (5 different levels, 5 presentations at each, for a total of 25 presentations) At each ________ of presentation, the number correctly detected is calculated Tester picks a percentage to use as _____________ (commonly 50%) o None of these have addressed ___________ bias (consider differences found between two people with the same threshold, but one responds conservatively, and the other more __________; one could be found to have a higher threshold, though it is really the same) Signal Detection Theory the modern methods view detection as a ____________ process See figure 3.5 and discussion Forced-Choice Procedures The usual way this procedure works is for the observer to attend to the __________ observation intervals. In one of the two intervals, a signal will be presented (this is randomized). The observer must decide which interval contained the signal. ___________ can occur in this type of testing (listener may tend to choose the first interval), however, the influence of a response bias as a result of criterion placement is virtually eliminated Adaptive Threshold Techniques - Threshold is usually defined as the level of a signal that yields a particular proportion correct on the ______________ function - Adaptive techniques can _______ the time it takes to find a threshold by choosing levels that converge towards a certain proportion correct (figure 3.8) Maximum Likelihood Yes-No Procedure - uses a “____________” paradigm and therefore had a defined observation period after which a judgment must be made - the listener’s response is used to estimate the probability that the response was drawn from a particular psychometric function chosen from a _______________ set spanning a range of values - as successive levels are tested, the most likely psychometric function emerges and from that function, _____________ can be determined advantages: o it can rapidly and efficiently provide estimates of threshold and ___________ rate o the _____________ of repeated threshold estimates is high Perceptual Attributes of the Auditory Stimulus - Loudness o all sounds that are ___________ have some degree of loudness o there is difficulty in measuring loudness, however people generally _______ on what loudness is and untrained ears can make reliable judgments on degree of loudness o most closely related to sound intensity; with all other factors held constant, changing the ___________ of a sound will change its loudness Pitch o not all audible sounds produce a discernable __________ o can be judged on a scale of _______ to _______, but also on how weak or strong the perceived pitch is o a __________ tone has a clear, unambiguous pitch over most of the range of hearing o other sounds producing strong pitches include complex ____________ sounds such as vowel sounds or musical instruments o for a steady-state harmonic sound, pitch is usually judged as being at or near the ______________ frequency (which is the reciprocal of the period) o pitch can be mediated by both the place of stimulation in the cochlea and by timing information from _________ fiber firings Timbre o Sounds can be equal in loudness and have the same pitch, yet be perceived _____________ (two musical instruments playing the same note) o this is related to the power spectrum shape and is referred to as ___________ o the study of the ability to discriminate differences in the shape of the power spectrum is called _____________ analysis Loudness, pitch and timbre are the main perceptual attributes of __________ Direct Psychophysical Scaling - We cannot directly measure the ______________ experience of an observer - We can however, quantify these experiences based on ______________ - “direct” psychophysical procedures involve the magnitude or quality of a perception being estimated directly by the observer - for example: a listener is presented with signals that differ in loudness. After each presentation, the listener assigns a ____________ based on how loud they perceive the sound to be. These numbers are then put together to form a __________ of loudness. Dynamic Range of Hearing The _________ range of hearing Characterized along coordinates of frequency and __________ pressure level Falls between the ___________ curve (threshold) and the loudest ___________ level (sounds that are too loud to listen to in comfort and/or cause damage) Studies of the lowest sound pressure level that is just detectable by the human ear as a function of frequency find two types: o Minimal audible ____________- measured for individual ears via earphone o Minimal audible __________- sounds are played over loudspeaker and both ears are used for detection the frequency response curves of the ear determined using the two above methods are similar in that they both have a sharp _______-pass cutoff within the octave between 10 and 20 kHz and both have a shallow ________-pass cutoff around just a few hertz the main difference in the two curves has to do with _________ versus binaural listening and that of an __________ ear canal versus an open one o the unoccluded ear canal has a resonant frequency corresponding to ¼ the wavelength near ________kHz o the occluded ear canal’s resonant frequency depends on the distance between the _________ and the occluding earphone the frequency response curve of the ear reflects the physical properties of the ____________ membrane (the primary site of tonotopic organization) physiologic noise such as internal body functions may limit the lowest levels that humans can hear, especially at very _________ frequencies the upper limit in level of the usable range of hearing is governed by the perception of ____________ (uncomfortable or damaging tend to define this level) Sensorineural hearing loss shows a reduction of the dynamic range and can result in ______________ ________________ (the abnormal growth of loudness) o sounds that would be at a comfortable level for a person with normal hearing would be uncomfortably loud for a person with ____________ Measuring the “Just Noticeable Difference” or Difference Limen for Pure Tones - JND- just-noticeable difference - In experiments measuring JNDs, all variables are held ___________ except for the one being measured - The listener is presented with ________ stimuli that differ slightly in regards to one variable and are asked to tell if the stimuli are the same or different - Measured for: o Pitch (DLF; difference limen for frequency) For pitch, it is the smallest difference in the frequency of two sounds that the human ear can detect For pure tones, it varies as a function of __________ frequency as frequency gets higher, the amount of difference required for the human ear to detect the two sounds as different becomes ___________ the DLF also varies as a function of ________ with the DLF becoming smaller as the signal becomes louder as duration goes below about 500 ms, the DLF _________ o Measured for Intensity (DLI, difference limen for intensity) Varies less with standard frequency than the DLF Decreases slightly for moderate to high level sounds played in __________ Why are such measures of interest? o JNDs provide insight into how accurately the ___________ properties of sound are represented in the auditory system o JNDs help us to evaluate models of __________ and of the auditory system o Comparison of JNDs is normal and impaired auditory systems may yield clues to the loss of accuracy in ________ sounds caused by auditory pathology. Some Just-Noticeable Difference Measures for Complex Sounds - there are many aspects of complex sounds that can be varied in discrimination experiments - Two fundamental aspects: o Discrimination of a change in the shape of the power spectrum Called ___________ ____________ analysis An underlying assumption is that spectral shape discrimination requires ____________ of the intensities at _______ or more frequencies falling in different regions of the spectrum This requires a different approach than that used for ____________ DLI experiments (see figure 3.9 and explanation on pages 40-41) The JND for spectral shape is greatest when the signal falls within the __________ to ___________Hz range The properties of the reference spectrum that allow the greatest sensitivity to alterations are _________ bandwidth and spacing of components roughly equal to every 1/3 octave o Discrimination of a difference in the shape of the amplitude envelope Temporal modulation transfer functions (TMTFs) relate the just-detectable depth of modulation to the ___________ of the modulator Masking - Refers to the decrease in the audibility of one sound due to the presence of another __________ - Used to ensure that the tone is truly being heard in the test ear and is not crossing over and being heard by the ________-_______ ear - “masking pattern” curve was determined by varying tones around a masker with ________ intensity and frequency - “psychophysical tuning curve” was determined by varying the ________ around a stimulus fixed in frequency and intensity - the effect of a narrowband masker is greater ___________ the frequency of the masker than ___________the frequency of the masker - as the level of the masker increases, this asymmetry or ___________ spread of masking increases - when a signal and masker are presented concurrently, certain interactions occur that can complicate interpretation of results o beats- audible fluctuations in the amplitude envelope that are a consequence of the ______________ of two or more frequencies - Temporal Masking- sounds can cause masking even if they do not overlap in time o forward masking- masking that occurs when the masking sound comes _________ the signal o backward masking- masking that occurs when the masking sound comes _________the signal Auditory Image Perception and Sound Source Discrimination - How can humans recognize sounds as separate auditory events that originate from different sources? How are some sounds recognized as near or far? How can we discriminate a bird, a voice and the ocean when all the acoustic information is in one signal? o Harmonicity- a property that causes discrete tones to be heard as a ________ sound o Spatial separation- sounds occurring from different _________ typically are from different sources and this are perceptually ___________ o Onset and offset synchrony and coherent modulation- sounds that begin or end together are likely to have come from the same _________ and thus tend to be grouped together perceptually. Common ___________ times with sounds tend to be very important. Binaural Hearing o advantages: localization- information on the __________ of the sound source suppression of the perception of __________(suppressed fast echoes so listener can focus on the direct sound source) extraction of a desired sound source embedded in many ___________ sounds o advantage comes from: ___________ time difference (caused by the distance between ears) ___________ attenuates sound at the far ear creating differences in level and spectral shape Psychoacoustic Measures of Listeners with Hearing Loss o must consider the amount of available _________ range o testing subjects with hearing loss presents some research problems: how do you present sounds? Based on a standard SPL level, or HL how do you select candidates for the research as patients with hearing loss vary so much as a individuals o the effects of hearing loss depend on multiple factors unilateral or bilateral loss cause of the hearing loss age of onset level of loss