decodingtxt

2 - Decoding auditory signals
Most young children learn language through hearing
and can easily master a second language within the
first decade of life. Rapin (1997) proposed that
“verbal auditory agnosia” may prevent some children
with autism from being able to decode rapidly
changing streams of speech [1]. Agnosia, an
impairment of recognition without sensory loss, seems
particularly relevant to the problems of children who
are echolalic. An echolalic child may be able to recite
a large repertoire of phrases, but displays a limited
capacity for rewording and creating new self-
generated utterances.

Failure to reword what has been heard indicates that
sub-units of meaning within phrases have not been
recognized. Brown (1975) quoted an autistic child's
repeated expression of exasperation, “What's the
matter, your truck stuck?” and pointed out that this
statement was more or less equivalent to “Damn!” [2].
This child was my son Conrad. I took Conrad to be
evaluated by Dr. Brown after reading in his book A
First Language: The Early Stages (Brown 1973), that
young children normally rely on stressed syllables to
extract essential units of meaning from the speech
they hear around them [3]. Brown and Bellugi (1964)
first determined the importance of stressed syllables
during analysis of early language development in
three children [4]. Auditory functions required for
recognizing stressed syllables and other acoustic
features may be diminished in the young autistic child
[5].

Language is a capability that evolved with
development of association tracts in the cerebral
cortex [6, 7]. However, language is normally learned
through hearing. This is why deafness is such a
serious handicap, and a child born deaf needs a great
deal of special education to develop an adequate
command of language [8].

Aboitiz et al. (2006) describe how elaboration of
auditory working memory may have led to evolution of
the cortical language areas [10].

In adults, decoding of streams of speech may take
place in the cortical association tracts. However,
Yakovlev and Lecours (1967) found that before age
four, myelination of cortical association tracts is not
yet complete; and they are not completely functional
until fully myelinated [11]. Yakovlev and Lecours, on
the other hand, discovered that brainstem nuclei in
the auditory system are fully myelinated before or
shortly after birth. Figure 6 shows the myelin stain in
the acoustic tectum of the midbrain at 29 and 25 fetal
weeks. That brainstem structures are myelinated
earlier than in the cerebral cortex suggests that
decoding of speech is more likely a function of the
brainstem auditory pathway during early language
development.

Angelo (1985) cited studies that indicate the
importance of parallel processing of speech signals
because they are received and understood at rates
well above the sequential resolving power of the ears
[12]. The parallel processing mechanisms appear to
be located in the brainstem and work by enhancing
features of signal changes. Angelo proposed that the
auditory system has evolved to actively search for
information. Vigilance for signal changes and ever-
present search for information developed no doubt as
a survival mechanism, but it is also well-suited to serve
the function of communication, especially in human
languages [13-15].

Rapin I (1997) Autism.
Brown R (1975) A collection
of words and sentences, an
autistic child.
Brown R (1973) A First
Language: The Early Stages.
Brown R, Bellugi U (1964)
Three processes in the
child's acquisition of syntax.
Benasich AA, Tallal P (2002)
Infant discrimination of rapid
auditory cues predicts later
language impairment.
Demonet JF et al. Renewal of
the neurophysiology of
language: functional
neuroimaging.
Price CJ. The anatomy of
language: contributions from
functional neuroimaging.
Gaustad MG et al. Deaf and
hearing students'
morphological knowledge
applied to printed English.
Fuess VL et al. Delay in
maturation of the auditory
pathway and its relationship
to language acquisition
disorders.
Aboitiz F et al. Cortical
memory mechanisms and
language origins..
Yakovlev PI, Lecours A.-R.
(1967). The myelogenetic
cycles of regional maturation
of the brain.
Angelo R (1985) Physiologic
acoustic basis of speech
perception.
Wilbrecht L, Nottebohm F.
Vocal learning in birds and
humans.
Warren RM. Auditory
perception and speech
evolution.
Ahmad Z et al. Auditory
comprehension of language
in young children: neural
networks identified with fMRI.

Rapin I (1997) Autism. New England Journal of Medicine 337:97-104.
Brown R (1975) A collection of words and sentences, an autistic child. In R Brown RJ
Herrnstein, Psychology (pp. 444-449). Boston: Little, Brown and Company.
Brown R (1973) A First Language: The Early Stages. Cambridge, MA: Harvard University
Press.
Brown R, Bellugi U (1964) Three processes in the child's acquisition of syntax. Harvard
Educational Review 34:133-151.
Benasich AA, Tallal P (2002) Infant discrimination of rapid auditory cues predicts later
language impairment. Behav Brain Res. 2002 Oct 17;136(1):31-49.
Demonet JF, Thierry G, Cardebat D. Renewal of the neurophysiology of language:
functional neuroimaging. Physiol Rev. 2005 Jan;85(1):49-95.
Price CJ. The anatomy of language: contributions from functional neuroimaging. J Anat.
2000 Oct;197 Pt 3:335-59.
Gaustad MG, Kelly RR, Payne JA, Lylak E.Deaf and hearing students' morphological
knowledge applied to printed English. Am Ann Deaf. 2002 Dec;147(5):5-21.
Fuess VL, Bento RF, da Silveira JA. Delay in maturation of the auditory pathway and its
relationship to language acquisition disorders. Ear Nose Throat J. 2002 Oct;81(10):706-
10, 712.
Aboitiz F, Garcia RR, Bosman C, Brunetti E. Cortical memory mechanisms and
language origins. Brain Lang. 2006 Jul;98(1):40-56.
Yakovlev, P. I. & Lecours, A.-R. (1967). The myelogenetic cycles of regional maturation
of the brain. In A. Minkowski (Ed.), Regional Development of the Brain in Early Life (pp. 3-
70). Oxford: Blackwell Scientific Publications.
Angelo R (1985) Physiologic acoustic basis of speech perception. Otolaryngologic
clinics of North America. 18:285-303.
Wilbrecht L, Nottebohm F. Vocal learning in birds and humans. Ment Retard Dev Disabil
Res Rev. 2003;9(3):135-48.
Warren RM. Auditory perception and speech evolution. Ann N Y Acad Sci. 1976;280:708-
17.
Ahmad Z, Balsamo LM, Sachs BC, Xu B, Gaillard WD. Auditory comprehension of
language in young children: neural networks identified with fMRI. Neurology. 2003 May
27;60(10):1598-605.