This week at Hearing International we are pleased to have two guest authors, Mr. Arun Kumar Yadav and Mr. Himanshu Kumar Sanju from the Department of Audiology and Speech Language Pathology, Amity Medical School, Amity University, Gurgaon, Haryana, India.  

Introduction

According to ASHA (2005), Central Auditory Processing Disorder (CAPD) refers to ‘difficulties in the perceptual processing of auditory information in the Central nervous system as demonstrated by poor performance in one or more of the auditory and temporal skills such as sound localization and lateralization, auditory discrimination, auditory pattern recognition and temporal aspects of audition:

  1. CAPD affects a diverse population and has been assumed to be associated with many different causes which include neuroanatomical anomalies, neuromaturational delay and neurologic insult of the central auditory nervous system (CANS). The main complaints and symptoms associated with CAPD are auditory, however, due to abnormal brain organization, functional discrepancies can commonly appear in areas of concentration, attention, cognition, language, communication, and learning (Boscariol et al, 2017).
  2. Temporal processes constitute the major component of auditory functions such as auditory discrimination, binaural interaction, pattern recognition, localization and lateralization, speech redundancy, and binaural integration but in CAPD populations, the temporal processing is poor (Schow et al, 2000). The physiology behind neural mechanisms for temporal processing have been evaluated by various behavioral and objective tests. Behavioral tests require many auditory processes such as attention, memory and perception.
  3. The Central Auditory Processing Disorders (CAPD) have acknowledged significant consideration over the last few years. In the present era, CAPD is not a novel condition under discussion especially in hearing science. For many decades, audiologists have been conscious that some persons with normal test findings for peripheral functions are delinquent in understanding speech. CAPD has always been associated with the problems concerning the processing of auditory signals, and audiologists have been consulted to undertake this diagnosis of APD based upon a series of tests. A new perspective towards which the attention of the audience has been drawn is associated with the controversies regarding the definition of APD, the mixed nature of APD, and an appropriate test series for APD assessment (Hurley, 2004).
  4. The controversy primarily relates to the characterization of APD with multi-sensory deficits. Some researchers claim that if multi-sensory deficits are existing, then the identification of APD with the discussed traits are unsuitable, and the diagnosis is only suitable where it involves only a single auditory deficit (Cacace and McFarland, 1988) (See Figure 1, right).

Symptoms of CAPD

A person with APD experiences difficulty in auditory discrimination and shows reduced abilities to differentiate between speech sounds. Persons with CAPD may experience difficulties in understanding speech amidst background noise. Individuals with CAPD have trouble in understanding what is being said to them in noisy situations like cafeteria, railway station, bus stop, road traffic and classroom. Individuals with CAPD may process thoughts and ideas slowly but may have difficulty in explaining them. They may experience discrepancies between expressive and receptive language skills and difficulties in auditory memory. Individuals with CAPD may be unable to remember auditory information or follow multiple instructions. Persons with CAPD may show poor musical abilities and not be able to recognize sound patterns or rhythms, and have poor vocal prosody in speech production.

Noise-induced hearing loss (NIHL)

 Noise is the most common occupational and environmental hazard. Noise can be described in terms of intensity (perceived as loudness) and frequency (perceived as pitch). Together the intensity and duration of noise exposure determines the potential for damage to the hair cells of the inner ear. Even sound perceived as comfortably loud can be harmful. After presbycusis, noise-induced hearing loss (NIHL) is the second most common form of sensorineural hearing loss. Shearing forces caused by any form of sound may have an impact on the stereocilia of hair cells of the basilar membrane of the cochlea, when excessive, these forces can cause cell death. NIHL begins at the higher frequencies (3000 to 6000 Hz) and develops gradually because of chronic exposure to excessive sound levels (Rabinowitz, 2000). Prolonged exposure to noise at high intensity is associated with damage to the sensory hair cells of the inner ear and development of permanent hearing threshold shift, as well as poor speech in noise intelligibility. To be audible, sounds must apply a shearing force on the stereocilia of the hair cells lining the basilar membrane of the cochlea. When extreme, this force may lead to cellular metabolic overload, damage of the cell and cell death. NIHL therefore denotes excessive “wear and tear” on the delicate inner ear structures. Other than hearing loss, Temporary Threshold Shift (TTS) and tinnitus are two other common symptoms related to NIHL. TTS is a temporary change in hearing sensitivity following an exposure to noise. TTS exists for a short duration of time. Literature reported that TTS on a regular basis can lead to Permanent Threshold Shift (PTS) i.e. a permanent change in hearing sensitivity (damage of cochlea). The noise exposure causing TTS changes the delicate micromechanics of the cochlea, which includes linkages between hair cell stereocilia, and indicates that the reversibility of such insults may not be 100%. The other warning sign for NIHL is tinnitus. Chronic tinnitus is experienced after a prolonged exposure to noise as a warning sign of cochlear damage. The ringing sound is considered to be caused by hair cells and neurons which are actually in the process of damaging the hair cells. Hair cells produce a neural injury discharge because the breakdown of cell membrane causes repeated depolarization (excitation) and uninhibited release of neurotransmitters. It is well established that the initial neural injury discharge extablishes (synaptic) connections in a network of auditory neurons at a more central (cortical) brain level, and these cells continue to fire spontaneously. There is also sufficient evidence supporting the fact that noise exposure frequently leads to tinnitus which might be due to alterations of the central auditory function (Henderson et al, 2011). Recently, a study done by Henry and Heinz (2016) reported distorted tonotopic coding of temporal envelop and fine structure among noise induced hearing loss subjects. They reported that coding of slower envelop structure lost the tonotopicity in cases of noise induce hearing loss. They also found that in apical fibers broadened tuning curve were observed without a significant shift in best frequency. These distortion of temporal fine structure interrupt tonotopicity, an essential principle of auditory processing required for robust signal coding. In the adult population, it may significantly influence the quality of life, and constitute a major limitation in relation to hearing-critical jobs, decreasing the potential worker’s chance of employment. Thus, NIHL not only affects hearing , but is also a major social problem.

Conclusion

According to Henderson et al. in 2011, prolonged exposure to noise of high intensity is related with damage to sensory hair cells and frequent exposure leads to tinnitus which might be due to alterations in the central auditory system. They have investigated the influence of exposure to annoying quality of noise reduces the processing capacity and injures the auditory system. Existing literature suggests that damage to the peripheral auditory system is supported by evidences (Henderson et al, 2011). But, existing studies showed the chance of damage to the CANS in this population. There are no literature records till date, investigating central auditory processing evaluation among individuals working in noisy environment. So, there is a need to investigate central auditory processing in individuals working in noisy environment. Early diagnosis and intervention of CAPD could help in providing a better quality of life for individuals working in noisy environment. So, CAPD lies within the role and scope of practice of industrial audiologists to evaluate central auditory processing in the affected individuals on a regular basis other than a routine peripheral audiological evaluation, as prevention is better than cure. 

 

 

About the Guest Authors:

Arun Kumar Yadav has post-graduate degree in Audiology and Speech Language Pathology from Amity University Haryana, India and is currently working as a faculty at Department of Audiology and Speech-Language Pathology at Amity Medical School, Amity University, Gurgaon, Haryana, India. Arun Kumar Yadav has expertise in noise induced hearing loss, hearing aids, implantable device and electrophysiology.

Himanshu Kumar Sanju has a post-graduate degree in Audiology from All India Institute of Speech and Hearing, Mysore-6, Karnataka, India and is currently working as an Assistant Professor-1 at Department of Audiology and Speech-Language Pathology at Amity Medical School, Amity University, Gurgaon, Haryana, India. His areas of special interest are vestibular assessment and management, electrophysiology, hearing aids, psychoacoustics, implantable devices and CAPD.

 

References:

American Speech-Language-Hearing Association. (2005) (Central) auditory processing disorder.  www.asha.org. Retrieved August 22, 2017.

Boscariol M., Garcia V., Guimarães, C., Montenegro, M., Hage, S., Cendes, F., & Guerreiro, (2010).. Auditory processing disorder in perisylvian syndrome. Brain Dev.,

     32(4):299-304.  Retrieved August 22, 2017.

Cacace,  A., Mcfarland,  D.(1988). Central auditory processing disorder in school-aged children: a critical review. J Speech Lang Hear Res., 41(2):355-73.  Retrieved August 22, 2017.

Henderson, D., Bielefeld, E., Lobarinas, E., & Tanaka, C. (2011). Noise-induced hearing loss: implication for tinnitus. In Textbook of Tinnitus (A. Moeller, Ed), Springer:  New York.301-309.

Henry, K., Kale, S. & Heinz, M. (2016). Distorted Tonotopic Coding of Temporal Envelope and Fine Structure with Noise-Induced Hearing Loss. J Neurosci. Vol. 36(7):2227-37.

Hurley, A. (2004).  Behavioral and Electrophysiological Assessment in Children with a Specific Temporal Processing Disorder (Doctoral dissertation submitted to the faculty at Louisiana State
     University).  Retrieved August 22, 2017.

Rabinowitz, P.(2000).  Noise-induced hearing loss. American family physician. Vol. 61(9):2759-60. Retrieved August 29, 2017

Schow, R., Seikel, J., Chermak,  G. &  Berent, M.(2000). Central auditory processes and test measures: ASHA 1996 revisited. Am J Audiol. 9(2):63-8. Retrieved August 22, 2017

 

 

 

The big event of 2017 in the United States is the total eclipse of the sun happening today, August 21, 2017 at various times ar0und the country.  It is the first total eclipse visible in the United States since 1979, which makes it a bit of a special event for young and old alike.  States across a swath of the US from Oregon to South Carolina and 11 other states in between with normally sleepy little towns that will become rather large cities for a day or so as the eclipse moves from obscuring the sun to total darkness.  Anyone within the path of totality can see one of nature’s most awe inspiring sights, a total solar eclipse. This path, where the moon will completely cover the sun and the sun’s tenuous atmosphere – the corona – can be seen, will stretch from Salem, Oregon to Charleston, South Carolina. Observers outside this path will and including the rest of N America, the northern part of S America and parts of W Europe and Africa, must be content with a partial In somesolar eclipse. Britain will only see a brief and shallow partial eclipse as the Moon clips the bottom edge of the Sun just prior to sunset.  The next one through the US will take place in April, 2024 so truly it is uncommon and unique experience.  Many families that have traveled hundreds (even thousands) of miles to a remote location to experience the eclipse, some in their motor homes, travel trailers, and other vehicles and others simply taking an eclipse tour today to make the most of this 2 minute and 45 second natural phenomenon. 

What of the Sounds of an Eclipse?  Can you Hear it?  Is it just a Visual Experience? 

Scientists will be studying this eclipse like none other with investigations from National Aeronautics and Space Administration (NASA) as well as many other solar research projects big and small around the US and worldwide.  While many of these studies look at the Sun’s Corona and its effects on the ionosphere and other indicate specific issues, there are others that will watch the animals as their world changes from day to night and back again.  Due to the change in light, nocturnal animals stir into action, while diurnal animals settle. As the sun’s light re-emerges, it often triggers what scientists call a ‘false dawn chorus.'”  Becker (2017) says that, “Solar eclipses confuse the hippos and piss of the pigeons”.   Previous eclipses have demonstrated that the change of light disrupts the bathing habits of hippos, and there is an increase of bug activity, particularly mosquitoes.  In the 1932 eclipse in California there were reports that crickets became excessively chirpy during totality, but cicadas stopped singing.  Bees, however, are disrupted as they return to their hives to make nectar during the darkness.  The behavior of birds appears to depend upon the species and while Owls hoot during totality, doves go quiet. and water birds like egrets stopped feeding and took off for their nighttime roosts. When the Sun reappeared, the doves “greeted the reappearance of light with a dawn chorus.  In previous eclipses hens stood completely still during totality, swallows acted normally, and pigeons became “agitated and aggressive.”  Christensen (2017) discusses pets and how they react to the eclipse,  “A study from the 1970s found that pet rabbits mostly slept. A few caged birds got agitated. Some dogs ignored the eclipse; a few seemed scared; a few barked when it was over. Cats, well, cats were cats. Some played, some meowed, but for the most part they slept, again showing off their best quality, as anyone who owns a cat knows: Our feline friends think the sun and the moon revolve around them, so what’s the big deal about a more little shade?”  Check out the Video on Animal behavior by clicking on the picture of the moon/sun to the right.  Click on the Innovation Now audio and find out how important it is to listen to the eclipse and not just “see”

The Eclipse Soundscapes Project uses sound to create a multisensory eclipse experience. The app, available from both the Apple App store and the Play store, includes audio descriptions of the eclipse in real time, as well as recordings of environmental sounds that tend to change during an eclipse. Users can even visualize the eclipse through touch, using the app’s interactive “rumble map”, vibrating the phone as totality approaches.   “For individuals who cannot see, hearing is an ideal way to experience the eclipse, since soundscapes change dramatically as the moon passes between the Earth and sun,” Eclipse Soundscapes representatives wrote on the project’s website. 

If you missed hearing this eclipse, you will have another chance in April of 2024.

 

References:

Becker, R. (2017).  The eclipses effects on animals will be wild.  The Verge.  Retrieved August 21, 2017.

Christensen, J., (2017).  Help solve an ancient mystery about the eclipse: Figure out what the animals do.  CNN.  Retrieved August 2, 2017.

Videos:

Christensen, J. (2017).  Help solve an ancient mystery about the eclipse: Figure out what the animals do.  CNN.  Retrieved August 21, 2017.

Innovation Now (2017).  Hearing the Eclipse.   Retrieved August 21, 2017.