This site has been prepared for researchers interested in the perceptual effects and how that may influence speech. The effects that are found here are the McGurk effect, the Lombard effect, delayed auditory feedback, Doppler effect and Stoop effect. Speech perception is how the listener uses acoustic and sensory cues and integrates them to arrive at phonetic decisions. People use sight, sound, and other sensory cues in speech recognition. This bi- and multi-modal method of speech perception involves the brain integrating sensory information into recognizable speech. The listener not only uses the acoustic cues but also other sensory input such as visual cues and environmental impute to perceive and identify speech signals.
McGurk Effect
The importance of visual cues can best
be observed in the phenomenon known as the McGurk
effect (demonstration).
Dr.
Harry McGurk and John MacDonald accidentally found this effect when
they were studying how infants perceive speech at different stages of development.
McGurk effect is an audio-visual illusion where an individual sees one
visual cue (ba), hears a different auditory cue (ga), and then perceives
(da), a completely different speech sound. The McGurk effect has influenced
the development of 3-D computerized
talking heads which have facial movements (visual and verbal cues).
They are being used to teach speech to people who are deaf, learning a
new language or having difficulty learning their native language. It is
also being considered as a tool to help people with dyslexia learn
to hear, talk, and read better. Studies have shown that the combination
of visual and auditory cues greatly increases the listener’s ability to
identify speech.
The Lombard
effect demonstrates how the perception of speech changes because of
the noise level in the environment. This effect causes the speaker to change
their voice level according to the noise level in the surrounding environment.
A person in a room with loud background noise will raise their voice level
to be louder or a person in a quiet room such as a library will lower their
voice level so it will be softer. Etienne Lombard first reported
this effect in 1911. Certain radio communicators such as emergency personnel,
aviators, and the space shuttle launch personnel experience this phenomenon.
Multiple
speech communication systems are being used to help eliminate the need
to raise the intensity of the speaker’s voice. The use of these systems
help to alleviate the possibility of hearing fatigue or hearing loss by
the operator.
Speech perception plays an important role
in speech production as is evident in delayed
auditory feedback (DAF). A speaker hears his own voice while speaking
and then tends to alter his voice according to what he hears. DAF can be
used to alter the perception of normal speech by delaying the duration
of the auditory signal. A speaker’s reaction to DAF is similar to stuttering
and is very disturbing to the speaker. This effect shows the importance
of the timing of the acoustic signal in speech perception. DAF is often
used as a tool in the treatment of stuttering.
http://www.kayelemetrics.com/daf.htm
This site produced by KAY Electronics is about the latest models of equipment used in delayed auditory feedback.
http://www.speech.psychol.ucl.ac.uk/FAF.html
This site contains information on the use of Altered Auditory Feedback for individuals that stutter.
http://www.hip.atr.co.jp/departments/Dept1/progress92/node10.html
This site contains notes on the research progress being made on the interaction between speech production and perception.
The Doppler effect
was first discovered by Christian
Johann Doppler in 1942. He first described the effect as an apparent
variation in the frequency of an emitted wave, as the source of the sound
moves toward or away from the observer. If you have heard an ambulance
siren or a car horn as it passes and noticed a change in the sound,
you have encountered the doppler
effect. For example, as an ambulance moves towards an observer, he
hears the high pitch sound of its siren. As the ambulance moves away,
the pitch of the siren rapidly drops. This is the phenomena known as the
doppler effect. The Doppler effect can be observed in other areas such
as the radar police use and the radar used in weather forecasting.
The only difference is instead of sound waves, radio waves are used.
The stroop effect or stroop task was named after John Ridley Stroop, who developed the experiment in the 1930's. This very interesting phenomenon shows how the automatic process of reading a color word "green" will interfere with the task of naming the color of the word (red). There is some evidence that when this interference, know as the Stroop effect occurs the part of the brain that is active is the anterior cingulate area.