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After surgery removed part of his visual cortex, the brain's main area for sight, a patient known as D.B. said he was completely blind in part of his visual field. Yet when researchers asked him to guess the position or orientation of objects there, he was right far more often than chance.

Lawrence Weiskrantz, patient D.B. research

MindScience

The story behind the card

D.B.'s operation, in 1973, removed a tangle of abnormal blood vessels from the back of the right side of his brain. Lawrence Weiskrantz and colleagues described his case in the journal Brain in 1974 and coined the word blindsight for it: responding correctly to things one cannot consciously see. One explanation is that the eyes do not send signals only to the visual cortex; some fibres go to older structures such as the superior colliculus in the midbrain, which helps steer the eyes and head and is found in some form in all vertebrates. Blindsight matters in debates about consciousness because it shows the brain can use what the eyes take in without the person having any experience of seeing.

Türkçe oku
D.B. olarak bilinen bir hasta, beynin görmeyi işleyen ana bölgesi olan görme korteksinin bir kısmı ameliyatla alındıktan sonra görme alanının bir bölümünde tamamen kör olduğunu söyledi. Ama araştırmacılar ondan oradaki nesnelerin yerini ya da yönünü tahmin etmesini istediğinde, şansla açıklanamayacak kadar sık doğru bildi.

D.B. 1973'te, beyninin sağ arka bölümündeki anormal bir damar yumağını aldırmak için ameliyat olmuştu. Lawrence Weiskrantz ve arkadaşları vakayı 1974'te Brain dergisinde anlattı ve bilinçli olarak görülmeyen şeylere doğru tepki verme hâline “körgörüş” adını verdi. Bir açıklamaya göre gözden çıkan sinyallerin hepsi görme korteksine gitmez; bir kısmı orta beyindeki üst tümsecik gibi daha eski yapılara ulaşır. Göz ve baş hareketlerini yönlendirmeye yardım eden bu yapı, bir biçimde bütün omurgalılarda bulunur. Körgörüş bilinç tartışmalarında önemlidir, çünkü beynin gözden gelen bilgiyi, kişi hiçbir şey gördüğünü fark etmeden de kullanabildiğini gösterir.

Sources and further reading

Background reading: Blindsight
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