Listener fatigue (also known as listening fatigue or ear fatigue) is a phenomenon that occurs after prolonged exposure to an
auditory stimulus. Symptoms include tiredness, discomfort, pain, and loss of sensitivity. Listener fatigue is not a clinically recognized state, but is a term used by many professionals. The cause for listener fatigue is still not yet fully understood. It is thought to be an extension of the
quantifiable psychological perception of sound. Common groups at risk of becoming victim to this phenomenon include avid listeners of music and others who listen or work with loud noise on a constant basis, such as musicians, construction workers and military personnel.
Causes
The exact causes of listener fatigue and the associated pathways and mechanisms are still being studied. Some of the popular theories include:
Introduction of artifacts in audio material
Musicality, especially on the radio, contains musical aspects (timbre, emotional impact, melody), and artifacts that arise from non-musical aspects (
soundstaging,
dynamic range compression
Dynamic range compression (DRC) or simply compression is an audio signal processing operation that reduces the volume of loud sounds or amplifies quiet sounds, thus reducing or ''compressing'' an audio signal's dynamic range. Compression is ...
, sonic balance). The introduction of these sonic artifacts affects the balance between these musical and non-musical aspects. When the volume of music is higher, these artifacts become more apparent, and because they are uncomfortable for the ear, cause listeners to "tune out" and lose focus or become tired. These listeners may then unconsciously avoid that type of music, or the radio station they may have heard it on.
Sensory overload
When exposed to a multitude of sounds from several different sources,
sensory overload
Sensory overload occurs when one or more of the body's senses experiences over-stimulation from the environment. There are many environmental elements that affect an individual. Examples of these elements are urbanization, crowding, noise, mass m ...
may occur. This overstimulation can result in general fatigue and loss of sensation in the ear. The associated mechanisms are explained in further detail down below. Sensory overload usually occurs with environmental stimuli
and not noise induced by listening to music.
Physiology
As with any type of hearing-related disorder, the related physiology is within the
ear
An ear is the organ that enables hearing and, in mammals, body balance using the vestibular system. In mammals, the ear is usually described as having three parts—the outer ear, the middle ear and the inner ear. The outer ear consists of ...
and
central auditory system. With regards to listening fatigue, the relevant mechanical and biochemical mechanisms primarily deal with
inner ear
The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the ...
and
cochlea
The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory org ...
.
Associated anatomy
The stereocilia (hair cells) of the inner ear can become subjected to bending from loud noises. Because they are not regeneratable in humans, any major damage or loss of these hair cells leads to permanent hearing impairment and other hearing-related diseases. Outer hair cells serve as acoustic amplifiers for stimulation of the inner hair cells. Outer hair cells respond primarily to low-intensity sounds.
Relevant mechanisms
Vibration
Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin ''vibrationem'' ("shaking, brandishing"). The oscillations may be periodic function, periodic, such as the motion of a pendulum ...
Excessive vibrations that occur in the inner ear can result in structural damage that will affect hearing. These vibrations result in an increase in the metabolic demands of the auditory system. During exposure to sound, metabolic energy is needed to maintain the relevant electrochemical gradients used in the transduction of sounds. The extra demands on the metabolic activity of the system can result in damage that can propagate throughout the ear.
Temporary threshold shifts
When exposed to noise, the human ear's sensitivity to sound is decreased, corresponding to an increase in the
threshold of hearing
The absolute threshold of hearing (ATH) is the minimum sound level of a pure tone that an average human ear with normal hearing can hear with no other sound present. The absolute threshold relates to the sound that can just be heard by the organis ...
. This shift is usually temporary but may become permanent. A natural physiological reaction to these threshold shifts is
vasoconstriction
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vessel ...
, which will reduce the amount of blood reaching the hair cells of the organ of Corti in the cochlea. With the resultant oxygen tension and diminished blood supply reaching the outer hair cells, their response to sound levels is lessened when exposed to loud sounds, rendering them less effective and putting more stress on the inner hair cells. This can lead to fatigue and temporary hearing loss if the outer hair cells do not get the opportunity to recover through periods of silence. If these cells do not get this chance to recover, they are vulnerable to death.
Temporary threshold shifts can result in different types of fatigue.
=Short-term fatigue
=
Recovery from temporary threshold shifts take a matter of minutes and shifts are essentially independent of the length of exposure to the sounds. Also, shifts are maximal during and at frequencies of exposure.
=Long-term fatigue
=
Long-term fatigue is defined as full recovery from temporary threshold shifts taking at least several minutes to occur. Recovery can take up to several days. Threshold shifts that result in long-term fatigue are dependent on level of sound and length of exposure.
Potential risk factors
Temperature and heat exposure
The
temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
and heat levels of the body are directly correlated with the temporary threshold shifts of the ear. When the levels of blood temperature increase, these threshold shifts increase as well. The transduction of sounds requires an oxygen supply that will be readily depleted due to the prolonged threshold shifts.
Physical activity
When combining
exercise
Exercise is a body activity that enhances or maintains physical fitness and overall health and wellness.
It is performed for various reasons, to aid growth and improve strength, develop muscles and the cardiovascular system, hone athletic ...
with exposure to loud noises, humans have been observed to experience a long temporary threshold shift as well. Physical activity also results in an increase in metabolic activity, which has already been increased as a result of the vibrations of loud sounds. This factor is particularly interesting due to the fact that a large population of people listen to music while exercising.
Hearing Aids
People who are deaf or hard of hearing and use hearing may be more likely to suffer listening fatigue because of the difficulties associated with their disability.
Experimental studies
Human
A study conducted in Japan reports fatigue sensation shown in subjects who listened to a metronome for six minutes.
A metronome was used as part of a technique to test the effects of musical and rhythmic stimulation in physical rehabilitation programs. After a series of tests involving physical therapy exercises while songs with different tempos played, subjects were asked to evaluate their own levels of fatigue. The results showed no statistically significant difference between fatigue levels with and without listening to various music. However, many patients that did respond with fatigue after music recorded the highest level of fatigue possible on the evaluation scale. This experiment paves the way for further study in distinction of the perception of listening fatigue between individuals.
Lin et al., conducted an experiment in Taiwan that tested the effect of generation of reactive oxygen species on temporary threshold shift and
noise-induced hearing loss
Noise-induced hearing loss (NIHL) is a Hearing loss, hearing impairment resulting from exposure to loud sound. People may have a loss of perception of a narrow range of Frequency, frequencies or impaired perception of sound including hyperacusi ...
.
Subjects were employees at a steel manufacturing company and each one was assessed for personal noise exposure during work shifts. Statistical analysis yielded a correlation between exposure of higher-frequency sounds to lower temporary threshold shifts and greater levels of tiredness and hearing loss.
Animal
A multitude of animal studies have been conducted to help understand hearing loss and fatigue. It is difficult to quantify levels of fatigue in animals as opposed to humans. In the experiment done by Ishii et al., subjects were asked to "rate" their levels of fatigue. However, techniques used by Ishii et al. are not perfect, as the recorded fatigue levels were self-perceived and prone to bias.
Studies have been done on a variety of animal species, including guinea pigs and dolphins., rats, fish, and chinchillas.
However, these studies do, in their conclusions, associate levels of fatigue with prolonged exposure to high levels of sound.
Treatment and prevention
At first glance, it would seem that reducing the noise and volume would be sufficient to reduce or prevent listening fatigue altogether. However, it is evident that the issue is at least partly physiological in nature. In cases of sensory overload not related to purposeful listening of hazardous noises, common ear protection such as earplugs and earmuffs can help alleviate the issue.
See also
*
Auditory fatigue
*
Loudness war
The loudness war (or loudness race) is a trend of increasing audio levels in recorded music, which reduces audio fidelity and—according to many critics—listener enjoyment. Increasing loudness was first reported as early as the 1940s, with ...
References
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Cognitive neuroscience
Hearing