| Language comprehension and production are unique features of connections within and between the temporal and frontal lobes. Defects in these circuits of the cerebral cortex should therefore be sought as causes of language disorders. But also, how maturation of the cortical language areas is disturbed needs to be determined in children with developmental language disorders. Failure of normal language development is the most serious handicap for children with autism. Even those who appear to have achieved good to excellent command of language often suffered some delay. Cederlund and Gillberg (2004) in their study of 100 males with Asperger syndrome found 49 percent did not have normal language development at 2 years of age and stated it could not be concluded that the remainder had normal language development [1]. Residual problems of language delay are the stilted and pedantic use of phrases that sometimes seem tangential to context or make little sense. Comprehension of spoken language begins with reception of sound patterns in the left temporal lobe [2]. Spoken language evolved earlier than visual forms of communication (reading, writing, or sign language), and the cortical language areas must depend in large part on using acoustic information delivered by the auditory pathway. Sensors of vibrations (in water by fish, or in air by land-dwelling animals) provide a rudimentary vigilance function. Evolution of neural processing for subconscious attention (or background listening) enhanced this vigilance function. Angelo (1985) proposed that auditory attention evolved further into an active "information seeking system" based on an increasing capability for simultaneous (parallel) processing of the multiple features of environmental sounds [3]. Language must represent the pinnacle of this information-seeking system. Parallel (or multiplexed) signal analysis not only enhances awareness of events in ones surroundings, but also enables detection of the numerous distinctive features of speech. To investigate only the cortical language areas for causes of disability is to overlook the importance of auditory processing. Wernicke (1874) criticized scholars of language and thought in his day, for not taking into account the auditory basis of speech understanding [2]. Hyper-sensitivity to certain sounds, like vacuum cleaners, or the unexpected ringing of a telephone, is characteristic of children with autism. Covering of the ears is a well-recognized (if anecdotal) response. Hayes and Gordon proposed that auditory dysfunction in children with autism could be caused by middle ear problems [4]. Hyper-sensitivity may represent loss of inhibitory neurotransmission in the auditory system. Inhibitory neurons are responsible for habituation, detecting sound onset, then shutting off continuing stimulation, and relegating sounds like a ringing phone to background consciousness. On the other hand autistic children often appear oblivious to sounds that evoke a startle reaction in most people. Signs of auditory dysfunction should point to possible problems in handling acoustic signals, and the ability to detect distinctive sound features of speech that prevent learning to speak "by ear" as most children do. |
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