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Speech Science

11 Speech Perception: Thresholds, Loudness and speech Perception

TermDefinition
Threshold The point at which an observer (listener) correctly responds to the stimulus 50% of the time.
Types of Thresholds 1. Absolute Thresholds 2. Differential Thresholds
Types of Absolute Thresholds a) Detection Thresholds b) Intelligibility Thresholds
Detection Threshold -That point at which an observer (listener) correctly detects the presence or absence of a stimulus 50% of the time -Do not require that the observer recognize or identify the stimulus; . . . only that its presence be noticed.
Pure-tones are what type of thresholds Example of detection thresholds
Sensation Level -How much of the stimulus does the observer sense (notice)?
If an individual has a threshold of 40 dB at 1000 Hz, and you present a 1000 Hz pure tone at 60 dB, how much of that tone does he actually sense? 20db
If an individual has a threshold of 60 dB at 1000 Hz, and you present a 1000 Hz pure tone at 50 dB, how much of that tone does he actually sense? -10db
If an individual has a threshold of 25 dB at 1000 Hz, and you present a 1000 Hz pure tone at 60 dB, how much of that tone does he actually sense? 35db
If a person has a 20db Threshold at 500hz, at what intensity must a 500 Hz tone be presented in order to produce a 40 dB Sensation Level? 60db
If a person has a 30db Threshold at 500hz, at what intensity must a 500 Hz tone be presented in order to produce a 40 dB Sensation Level? 70db
If a person has a 50db Threshold at 500hz, at what intensity must a 500 Hz tone be presented in order to produce a 40 dB Sensation Level? 90db
If a person has a 60db Threshold at 500hz, at what intensity must a 500 Hz tone be presented in order to produce a 40 dB Sensation Level? 100db
Intelligibility Thresholds -That point db at which a listener can correctly perceive 50% of the stimuli presented. -Now not just do you hear it but can you tell me what it is. (not just detection, but perception) -The more informative the stimuli the less intensity you need.
Differential Threshold -How different two stimuli must be in order for the observer to detect a difference -Ask how different must the in intensity, duration, frequency in order for the person to detect a difference. -Just Noticeable Difference (JND) -Difference Limen(DL)
Loudness the psychological correlate of intensity
Measurement of Loudness Phons
Phons the number of dB SPL at which a 1000 Hz pure tone must be presented in order to be judged equally loud.
How loud is a 60 Hz tone that is presented at 70 dB SPL? 40 Phons
How loud is a 200 Hz tone that is presented at 40 dB SPL? 20 Phons
How loud is a 4000 Hz tone that is presented at 75 dB SPL? 80 Phons
How many dB must you make a 200 Hz tone in order for it to be 50 Phons? 60 dB SPL
First acoustic cues a listener goes through to decode sound Is the sound harmonically structured or does it contains aperiodic noise (sonorant or obstruent)
How do we perceive a stop? -silence during pressure build-up -sudden onset (transient burst) -rapid formant transition, as articulators move quickly to adjacent vowel.
How do we perceive a fricative? -extended period of noise -greatest sound intensity is at high frequencies, then = sibilant /s,z,sh,ouge/ -low frequency, then= dental fricative /f,v,th,thz/ -if energy >4000 Hz, then = /s/ or /z/ -if energy> 2500 Hz but <4000 Hz, then= /sh/ or /ouge/
How do we perceive an affricate = stops with a fricative release -silence during pressure build-up -sudden onset -extended period of noise (fricative portion)
How do we perceive a nasal? -Very low frequency for first formant (nasal murmur) -Very weak intensity in upper formants, due to anti-resonances
How do we perceive a Semi-vowel (Glides /w,j/ and Liquids /r,l/) -Have formant transitions, but unlike vowels, these are not steady-state sounds, and are characterized by movement of the articulators.
How do we perceive Vowels -comparatively low frequency, long sounds with great intensity. -Relative positioning of formants is key to distinguishing one vowel from another.
3 points of the Motor Theory of speech perception 1)There is a link between speech perception and speech production. 2)A listener extracts info about articulation from the acoustic signal 3)This information allows the listener to cope with problems of variability, segmentation, and speaking rate.
Created by: aramos139