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Chapter 6

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PSYC 212
Jelena Ristic

Chapter Six The Auditory System: Perceptual Aspects of Hearing Chapter Outline In this chapter, you will learn about hearing, which is the perceptual experience that results from the processing of auditory signals. Various perceptual features are discussed and you will gain an understanding of how we are able to determine the location of a sound source—this is an interesting capability of our auditory system because the sound signal itself provides no cue to its origin. To begin, you will learn about the absolute threshold for detection of an auditory stimulus and difference thresholds, as well as the procedures used to determine these thresholds. The sone scale of loudness will be explained and the intensity–loudness relationship will be discussed. You will learn the 10 decibel rule, which states that the perception of loudness is doubled with a 10 decibel increase in sound intensity. The perception of frequency and pitch is discussed next. Humans can detect sound frequencies in the range of 20 to 20,000 Hz. Frequencies below this range are called infrasonic and those above are ultrasonic. Many animals can detect ultrasonic sound frequencies. Acoustic pitch is discussed and you will learn that there is not an exact relationship between pitch and frequency. An explanation of pitch coding mechanisms is then presented and in this context, you will examine the problem of the missing fundamental. The problem is simply this: we will perceive the fundamental frequency of a harmonic series when the fundamental frequency is not actually present in the stimulus. By definition, this is an illusory perception and any theory of pitch perception must be able to account for this finding. The final section of the chapter addresses our ability to localize sounds in our environment. Interaural intensity difference is one important cue that aids in our localization ability. This cue is based on the fact that the intensity of sound reaching each ear will differ based on which is ear is closer to the sound source. The other important cue is interaural time difference which relates to how long it takes sound to reach each the ear—the further the sound source is from the ear, the longer it takes sound to reach it compared to the ear closer to the sound source. The neural underpinnings of sound localization will also be described. Learning Objectives This chapter will help you 2  build on the information learned in chapter five, by relating the physical stimulus of audition to the perceptual experience. For example, you will understand that although the physical intensity of a sound can be held constant, our perception of how loud the sound is may be affected by many factors, both biological and environmental.  apply the concepts of psychophysics to audition through examples and demonstrations. You can experience the experimental methods and findings, as well as some of the auditory phenomena such as the missing fundamental and equal loudness contours themselves, by visiting the Auditory Demonstrations website and participating in the online demonstrations (http://www.santafevisions.com/csf/demos/audio/).  compare and contrast the different scales that have been developed to quantify the quality of sound. You should also be able to discuss each scale in terms of the relationship they describe between an aspect of the sound stimulus and the perceptual experience.  connect the physical property of frequency to the perceptual property of pitch and be able to explain how sounds of different frequencies affect the basilar membrane. You should also be able to connect previous learning of place and frequency theory to describe how activation in specific areas of the basilar membrane by different frequencies is coded such that we are able to make judgments of pitch.  explain how the human auditory system and brain use auditory signals such as interaural time difference and interaural intensity difference to localize sounds. You should also understand that, although humans are fairly accurate in localizing sounds, background noise, masking, and other factors can affect this ability.  describe and discuss the cocktail party effect in terms of what it tells us about our ability to ‘fill in’ missing sounds. You are encouraged to visit the Blind Source website for a demonstration of the cocktail party effect to further their understanding of the difficulty of the task (demonstration 3 at http://cnl.salk.edu/~tewon/Blind/blind_audio.html) 3 Study Questions True/False Indicate whether the statement is true or false. ____ 1. A disadvantage of the closed-ear method is that individual differences can result in different pressure being applied to the eardrums. ____ 2. Different frequencies can result in threshold sensitivity differences. ____ 3. The sone scale can be used as a loudness scale for all frequencies. ____ 4. Masking affects our perception of a particular sound in the presence of other sounds. ____ 5. An individual who is deaf in one ear is just as good at localizing sounds in the environment as an individual who is not deaf in either ear. Multiple Choice Identify the choice that best completes the statement or answers the question. 1. Which of Fechner’s methods can be used for obtaining the absolute threshold of hearing? a) Method of Adjustment b) Method of Limits c) Method of Constant Stimuli d) All three can be used 2. Humans are most sensitive
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