1. CSD 2230 INTRODUCTION TO HUMAN COMMUNICATION DISORDERS Normal Sound Perception, Speech Perception, and Auditory Characteristics at the Boundaries of the Lifespan

2. PowerPoint Access You may access this presentation through my website: http://www.d.umn.edu/~floven/ Just click on the CSD 2230 link on my home page.

3. The Perception of Sound What do we hear when we listen to a sound??

4. The Perception of Sound Psychoacoustics is a branch of experimental psychology interested in these questions

5. Overview of Perception n Although the physical characteristics used to measure sounds are objective, how we experience sounds is subjective Objective Characteristics Intensity Frequency Duration Subjective Characteristics Pitch Loudness

6. Questions to Ask What are the limits of our ability to sense sound? How do our subjective impressions of sounds change as we change the physical dimensions of sound?

7. Overview of Perception How we experience sounds is subjective Listeners are variable in their responses

8. Hearing Acuity What are our limits in detecting sounds? Audibility and detectability Frequency and intensity restrictions

9. Normal Auditory Sensitivity Normal hearing listeners are capable of detecting sounds within a range of 1 Hz up to about 20,000 Hz Sensitivity is NOT equal across this range Best sensitivity is between 1000-5000 Hz As the frequency of the sound moves above or below this range, sensitivity gets progressively worse

10. Auditory Area n The useful range of hearing for any individual is taken to be the area between the person’s absolute threshold and the threshold of feeling

11. The Normal Auditory Area Useful frequency range is between 20 and 20,000 Hz Dynamic range is widest between 1000 and 5000 Hz Widest range is 120 dB

12. Intensities of Common Sounds

13. Thresholds Absolute sensitivity--the minimum intensity at which a listener can distinguish sound from silence üDetection Differential sensitivity--the smallest change in a stimulus a listener is just able to detect nDiscrimination

14. Differential Sensitivity for Intensity Intensity discrimination depends on whether sounds are close to absolute threshold or far from threshold In general, for a wide range of stimulus intensities and frequencies, our discrimination ability for intensity is 2 dB or less

15. Differential Sensitivity for Frequency Our resolving power for frequency isn’t as good as for intensity Frequency discrimination depends on the general frequency range of the two sounds

16. Characteristics of Normal Sound Perception and Speech

17. Acoustic Cues of Speech 1. Frequency 2. Intensity 3. Temporal Characteristics

18. Categorical Perception Represents an important way in which speech is processed differently by humans than other sounds Illustrated by comparing our ability to discriminate and identify certain kinds of sounds

19. Categorical Perception Discrimination is the ability to tell if two sounds are the same or different Identification is the ability to label a sound

20. Sounds Perceived Non- Categorically n Music We can discriminate more than 1000 different notes (pitches) but most of us can only identify about 7. Big difference between what we can discriminate and what we can identify

21. Sounds Perceived Categorically n Speech n We can discriminate the same number of speech sounds (phoneme) that we can identify

22. Perception of Some Voiced vs. Unvoiced Consonants Discriminating /p/ from /b/, /t/ from /d/, or /k/ from /g/ These are English consonants that are formed the same way (manner of articulation) and formed in the same area (place of articulation) of the vocal tract but differ in terms of whether the vocal folds are vibrating during production (voicing)

23. Voice Onset Time The difference in these phoneme pairs is in the timing of when the larynx starts to vibrate during the production of the consonant voice onset time (VOT) Voiced stops have a relatively short VOT Voiceless stops have a longer VOT

24. VOT Waveform for a Voiceless Stop n VOT measure for /p/. LO represents the release of the burst (stop). RO is placed at the highest point of the first cycle of vocal fold vibration. Notice the relatively long time interval between these two points.

25. VOT Waveform for a Voiced Stop n VOT measure for /b/. LO represents the release of the burst (stop). RO is placed at the highest point of the first cycle of vocal fold vibration. Notice the relatively short time interval between these two points.

26. Categorical Perception of VOT n Identification functions of a single listener for VOT continuum from /d/ to /t/ in 11 ms steps.

27. Neat….Huh??? The big question is: Are we born with this ability to perceive speech categorically? Or Do we eventually learn to perceive speech categorically?

28. Infant Studies n Before birth When do we first hear? What do we first hear?

29. Infant Studies n Acuity after birth  How do we measure this?  Why is it important to know ASAP??

30. Nonbehavioral Measures of Hearing Acuity Auditory Brainstem Response (ABR) Otoacoustic Emissions (OAEs)

31. Behavioral Responses of Infants and Newborns n The auditory responses of infants can be described in terms of reflexive behaviors and attentive behaviors

32. Reflexive Behaviors to Loud Sounds n Reflexes observed when loud sounds are presented to an infant: n The startle response n The auropalpebral response

33. Attentive Behaviors in Newborns and Infants n Quieting responses n Increase in ongoing activities n Changes in breathing rate n Changes in vocalization n Eye widening and searching n Smiling or changes in facial expression

34. Attentive Behaviors in Newborns and Infants n The intensity of sounds needed to elicit these behaviors depends on the type of sound n For speech sounds, these behaviors are elicited at 60-80 dB SPL

35. Behavioral Responses of Infants n At around 4 months, infants start to demonstrate behaviors consistent with localization

36. Visual Reinforcement Audiometry n The younger infant 4 months-9 months

37. Visual Reinforcement Audiometry n The older infant 9 months-2 years

38. Infant Speech Perception Speech is learned the same way as any other motor behaviors Children DO NOT come into the world as blank slates Human infants are born with the capacity for categorizing may speech sounds in specialized ways

39. Infant Speech Perception n Eimas’ studies of the 1970s Infant subjects 1-4 months old Stimuli included computer generated speech sounds that varied in VOT to produce either /pa/ or /ba/ Responses included a non-nutritive sucking response Results suggested that the infants perceived changes in VOT categorically--just like adults

41. Infant Speech Perception n Werker’s studies of the 1980s: English speaking infants from 6 months-12 months of age Stimuli included phonemic contrasts from Salish and Hindi languages Responses included a non-nutritive sucking response Results suggested that the younger infants listening to the non- native contrasts were able to discriminate these speech contrasts with good accuracy, but the ability disintegrates progressively as the child ages Their ability to discriminate contrasts in their native language remained high

42. Three Important Conclusions Regarding Speech Perception Development Infants already come into the world with certain perceptual capacities for phonetic distinctions used in the world’s languages Experience with a particular language leads to decreased perceptibility of at least some non- native phonetic contrasts and enhanced perception of native contrasts By the end of the first year, the influence of a particular language is evident in the perception of non-native speech

43. Older Adults Changes in acuity usually begin around the third decade of life Incidence increases sharply as we age 25%-40% of people over 65 have significant hearing loss The figure changes to 90% by the time we reach our 80s

44. Hearing Loss and Aging No clear etiology (cause) Possible sources include: Noise exposure Genetics Vascular disease Systemic disease Diet Pollution Others

45. Audiologic Characteristics Associated with Aging n Acuity: n Changes in pure tone sensitivity (absolute thresholds) among older adults emerges gradually as age increases.

46. Changes in Detection as a Function of Age and Gender n Two trends are clear from these data: 1) Both males and females exhibit a significant loss in sensitivity by age 60, especially in the higher frequencies 2) Threshold values for males are poorer, overall, than for females

47. Audiologic Characteristics Associated with Aging Recruitment Abnormal growth of loudness commonly associated with damage to the cochlea Due directly to the reduced dynamic range Makes the ear more sensitive to loud sounds

48. Audiologic Characteristics Associated with Aging n Speech Perception n Speech perception suffers as we age, even if we control for the change in sensitivity associated with aging