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Spatial hearing loss, also known as spatial processing deficit, refers to a form of deafness that is an inability to use spatial cues, i.e. where a sound originates from in space, to understand speech in the presence of background noise.〔Cameron, S & Dillon, H (2008). The Listening in Spatialized Noise – Sentences Test: Comparison to prototype LISN test and results from children with either a suspected (central) auditory processing disorder of a confirmed language disorder. Journal of the American Academy of Audiology, 19(5).〕 ==Overview== People with spatial hearing loss have difficulty processing speech that arrives from one direction while simultaneously filtering out noise arriving from other directions. Research has shown spatial hearing loss to be a leading cause of central auditory processing disorder (CAPD) in children. Children with spatial hearing loss commonly present with difficulties understanding speech in the classroom.〔 Spatial hearing loss is found in most people over 70 years of age, and can sometimes be independent of other types of age related hearing loss.〔D.Robert Frisina, Robert D Frisina, Speech recognition in noise and presbycusis: relations to possible neural mechanisms, Hearing Research, Volume 106, Issues 1-2, April 1997〕 As with presbycusis, spatial hearing loss varies with age. Through childhood and into adulthood it can be viewed as spatial hearing gain (with it becoming easier to hear speech in noise), and then with middle age and beyond the spatial hearing loss begins (with it becoming harder again to hear speech in noise). Sound streams arriving from the left or right (the horizontal plane) are localised primarily by the small time differences of the same sound arriving at the two ears. A sound straight in front of the head is heard at the same time by both ears. A sound to the side of the head is heard approximately 0.0005 seconds later by the ear furthest away. A sound halfway to one side is heard approximately 0.0003 seconds later. This is the interaural time difference (ITD) cue and is measured by signal processing in the two central auditory pathways that begin after the Cochlea and pass through the Brainstem and Mid-brain.〔Marina S. Dobreva, William E. O’Neill and Gary D. Paige, Influence of Aging on Human Sound Localization, Journal of Neurophysiology 105, 2011.〕 Some of those with spatial hearing loss are unable to process ITD (low frequency) cues. Sound streams arriving from below the head, above the head, and over behind the head (the vertical plane) are localised again by signal processing in the central auditory pathways. The cues this time however are the notches/peaks that are added to the sound arriving at the ears by the complex shapes of the pinna. Different notches/peaks are added to sounds coming from below compared to sounds coming from above, and compared to sounds coming from behind. The most significant notches are added to sounds in the 4 kHz to 10 kHz range.〔Virginia Besta, Simon Carlile, Craig Jin and André van Schaik, The role of high frequencies in speech localization, Journal of the Acoustical Society of America 118(1), 2005.〕 Some of those with spatial hearing loss are unable to process pinna related (high frequency) cues. By the time sound stream representations reach the end of the auditory pathways Brainstem inhibition processing ensures that the right pathway is solely responsible for the left ear sounds and the left pathway is solely responsible for the right ear sounds.〔Della Penna S, Brancucci A, Babiloni C, Franciotti R, Pizzella V, Rossi D, Torquati K, Rossini PM, Romani GL, Lateralization of Dichotic Speech Stimuli is Based on Specific Auditory Pathway Interactions, Cerebral Cortex 17(10), 2007.〕 It is then the responsibility of the Auditory Cortex of the right hemisphere on its own to integrate the whole auditory scene. Information about the right auditory hemifield joins with the information about the left hemifield once it has passed through the Corpus Callosum - the brain white matter that connects homologous regions of the left and right hemispheres.〔At A, Spierer L, Clarke S, The role of the right parietal cortex in sound localization: a chronometric single pulse transcranial-magnetic stimulation study, Neuropsychologia 49(9), 2011〕 Some of those with spatial hearing loss are unable to integrate the auditory representations of the left and right hemifields. Conscious top-down processing enables attention to be given to a single auditory stream (such as the speech stream being listened to). A gain mechanism can then be employed involving the enhancement of the speech stream, and the suppression of any other speech streams and any noise streams.〔Kerlin J, Shahin A and Miller L, Attentional Gain Control of Ongoing Cortical Speech Representations in a “Cocktail Party”, Journal of Neuroscience 13; 30(2), 2010.〕 Those individuals with spatial hearing loss are not able to accurately perceive the directions different sound streams are coming from and their hearing is no longer 3D. Sound streams from the rear may appear to come from the front instead. Sound streams from the left or right may appear to come from the front. The gain mechanism can not be used to enhance the speech stream of interest from all other sound streams. Those with spatial hearing loss need target speech to be raised by typically more than 10 dB when listening to speech in a background noise compared to those with no spatial hearing loss.〔Glyde H, Hickson L, Cameron S, Dillon H, Problems hearing in noise in older adults: a review of spatial processing disorder, Trends in Amplification 15(3), 2011.〕 Spatial hearing ability normally begins to develop in early childhood, and then continues to develop into early adulthood. After the age of 50 years spatial hearing ability begins to decline.〔Sharon Cameron, Helen Glyde, Harvey Dillon, Listening in Spatialized Noise - Sentences Test (LiSN-S): Normative and Retest Reliability Data for Adolescents and Adults up to 60 Years of Age, Journal of the American Academy of Audiology 22, 2011.〕 Both peripheral hearing and central auditory pathway problems can interfere with early development. Aging of the peripheral and central auditory pathways accounts for the decline of spatial hearing in the elderly. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Spatial hearing loss」の詳細全文を読む スポンサード リンク
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