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Shifts in phonetic identification with changes in signal presentation level
The Journal of the Acoustical Society of America
|May 1, 1981
Summary
High sound pressure levels (SPLs) significantly alter speech sound perception, affecting how listeners categorize sounds like [b], [d], and [g]. Researchers recommend using equal SPLs, not equal sensation levels (SLs), for speech perception studies.
Area of Science:
- Speech Perception
- Auditory Neuroscience
- Psychoacoustics
Background:
- Understanding how sound pressure level (SPL) affects speech sound categorization is crucial for accurate auditory research.
- Previous studies have not fully explored the impact of varying SPLs on the perception of speech continua.
Purpose of the Study:
- To investigate the effect of different signal presentation levels (55, 70, and 90 dB SPL) on identification functions for a two-formant [bdg] speech continuum.
- To determine if high SPLs independently influence speech perception, separate from cochlear damage.
Main Methods:
- Utilized a two-formant continuum simulating speech sounds [b], [d], and [g].
- Presented stimuli at three distinct sound pressure levels: 55, 70, and 90 dB SPL.
- Assessed identification functions across these different presentation levels.
Main Results:
- At 90 dB SPL, significant shifts in categorization were observed: the [b] category narrowed, the [d] category was nearly eliminated, and the [g] category expanded.
- High SPLs demonstrably altered the identification functions for the tested speech stimuli.
Conclusions:
- High sound pressure levels can independently modify speech sound identification functions.
- Caution is advised when comparing speech perception between normal hearing and hearing-impaired listeners using high SPL stimuli.
- Perceptual experiments may yield more reliable results when conducted at equal SPLs rather than equal sensation levels (SLs).