TURAN ONUR BAYAZIT, Adile ÖNİZ, Murat ÖZGÖREN

Dikotik dinlemede dikkatin kulak tercihine etkisi

Dikotik dinleme testi; işitsel sistemdeki fonetik işlemlemenin asimetrisi çalışmalarında kullanılan girişimsel olmayan, uygulaması kolay ve düşük maliyetli bir yöntemdir. Sessiz-sesli harflerden oluşan hecelerin (consonant-vowel/CV) aynı anda, iki farklı kulaktan dinletilmesiyle yapılan testte, katılımcılar duydukları hece için yanıtlarını verirler. Klasik dikotik dinleme testi sonucunda sağlıklı kişilerin %65-90’nında sağ kulak tercih edilir. Kulak tercihi mekanizmasını açıklamak için anatomik bağlantılara dayanan duyusal (aşağıdan yukarıya işlemleme/bottom up processing) ve kortikal kontrolün (yukarıdan aşağıya kontrol/top down control) rol aldığı dikkate bağlı iki ana model ileri sürülmüştür. Bazı patolojik durumlarda yapılan çeşitli dikotik dinleme testi araştırmalarında, bu testin sol hemisferdeki merkezlerin normal çalışıp çalışmadığının belirlenmesi, dikkat eksikliğinin tespiti, kallozal transfer fonksiyonunun tayininde kullanılabileceği önerilmektedir. Amaç: Konuşma heceleri uygulanan sağlıklı gönüllülerde işitsel sistemde baskın hemisferin tayin edilmesi ve dikkat yönergesinin bu asimetrik yapıya etkisinin araştırılmasıdır. Ayrıca dikotik dinleme testinin Türk toplumu için geçerliliğinin değerlendirilmesidir. Gereç ve yöntem: 20 sağlıklı gönüllüye (20 sağlak, 12 erkek) 36 adet CV dikotik hece, dikkat hiçbir kulağa yönlendirilmeden (non-forced/NF), dikkat sağ kulağa (forced right ear attention/FR) ve sol kulağa (forced left ear attention/FL) yönlendirilerek uygulandı. Kişilerin verdiği yanıtlar yeni geliştirilen elektronik bir sistemle değerlendirildi. İstatistiksel analizde yineleyen ölçümlerde ANOVA testi kullanıldı. Bulgular: NF durumda ortalama %53,95 sağ kulak tercihi (REA), FR durumda %61,23 REA ve FL durumda %37,72 REA bulundu. FL durumda ise sol kulak tercihi %47,19 olup, NF ve FR durumundan yüksekti. Sonuç: Sağlıklı bireylerde sol hemisfer üstünlüğü bulunmaktadır. Yukarıdan aşağıya kontrol mekanizmasıyla kulak tercihi değiştirilebilmektedir. Burada uygulanan dikotik dinleme testleri Kulak Burun Boğaz, Odyoloji, Nöroloji, Psikiyatri ve ilgili diğer bilim dallarının işbirliğiyle geliştirilerek işitme merkezi hasarı ve dikkat bozukluğu hastalıklarının tayininde ve ayrıca bu hastalıkların tedavilerinin izleminde kullanılabilir.

The effect of the attention to ear advantage during Dichotic listening test

The dichotic listening test is a non-invasive, low cost and easy to apply technique used in studying asymmetry of phonetic processing. In this test, participants are presented with two syllables, one in each ear, simultaneously and are asked to declare the syllab le they hear. Syllables are constructed as consonant-vowel (CV) pairs. In the classical dichotic listening test, 65-90% of healthy individuals declare the syllable presented in the right ear. In order to explain this right ear advantage (REA), anatomical and attention- related models are proposed. According to these models, REA can be associated with left hemisphere dominance; besides, attention drive top down control can modify REA. It is suggested that this test can be used to investigate attention deficits, functioning of different areas in left hemisphere and callosal transfer function in studies of pathological conditions. Objective: Establishing dominant hemisphere of healthy subjects in auditory system and investigation of effect of instructional attention on this asymmetry. Also, correlation of this new Turkish version of the dichotic test results with other nation’s dichotic test results. Material and method: 36 CV syllable pairs were presented to 20 healthy subjects (all right-handed, 12 male) in three different conditions: no direction of the attention (nonforced, NF), directing attention to right ear (forced-right, FR), directing attention to left ear (forced-left, FL). Declarations of the heard syllable were recorded by a recently developed electronic system. In statistical analysis, repeated measures of ANOVA’s was used. Results: REA was 53.95% (±17.20) in NF condition, 61.23% in FR condition, 37.72% in FL condition. In FL condition, the rate of left ear advantage was found to be %47.19, which was greater than in NF and FR conditions. Conclusion: In healthy subjects, left hemisphere dominance was found. REA can be modified by top down control mechanisms. Dichotic listening test can be used in determination of conditions related to auditory cortex malfunctions and attention deficit disorders as well as in follow-up of medical treatments of these types of disorders.

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