Whistled Turkish alters language asymmetries

Whistled languages represent an experiment of nature to test the widely accepted view that language comprehension is to some extent governed by the left hemisphere in a rather input-invariant manner. Indeed, left-hemisphere superiority has been reported for atonal and tonal languages, click consonants, writing and sign languages. The right hemisphere is specialized to encode acoustic properties like spectral cues, pitch, and melodic lines and plays a role for prosodic communicative cues. Would left hemisphere language superiority change when subjects had to encode a language that is constituted by acoustic properties for which the right hemisphere is specialized? Whistled Turkish uses the full lexical and syntactic information of vocal Turkish, and transforms this into whistles to transport complex conversations with constrained whistled articulations over long distances. We tested the comprehension of vocally vs. whistled identical lexical information in native whistle-speaking people of mountainous Northeast Turkey. We discovered that whistled language comprehension relies on symmetric hemispheric contributions, associated with a decrease of left and a relative increase of right hemispheric encoding mechanisms. Our results demonstrate that a language that places high demands on right-hemisphere typical acoustical encoding creates a radical change in language asymmetries. Thus, language asymmetry patterns are in an important way shaped by the physical properties of the lexical input.