Therefore, assuming normal hearing exists around the dead region, it would produce an audiogram that has a dramatically steep slope between the frequency where a threshold is obtained, and the frequency where a threshold cannot be obtained due to the dead region. However, it appears that this is not the case. Dead regions cannot be clearly found via PTA audiograms. This may be because although the neurons innervating the dead region, cannot react to vibration at their characteristic frequency. If the basilar membrane vibration is large enough, neurons tuned to different characteristic frequencies such as those adjacent to the dead region, will be stimulated due to the spread of excitation. Therefore, a response from the patient at the test frequency will be obtained. This is referred to as “off-place listening”, and is also known as ‘off-frequency listening’. This will lead to a false threshold being found. Thus, it appears a person has better hearing than they actually do, resulting in a dead region being missed. Therefore, using PTA alone, it is impossible to identify the extent of a dead region (See Figure 7 and 8).Consequently, how much is an audiometric threshold affected by a tone with its frequency within a dead region? This depends on the location of the dead region. Thresholds at low frequency dead regions, are more inaccurate than those at higher frequency dead regions.
Colpocephaly is a cephalic disorder involving the disproportionate enlargement of the occipital horns of the lateral ventricles and is usually diagnosed early after birth due to seizures. It is a nonspecific finding and is associated with multiple neurological syndromes, including agenesis of the corpus callosum, Chiari malformation, lissencephaly, and microcephaly. Although the exact cause of colpocephaly is not known yet, it is commonly believed to occur as a result of neuronal migration disorders during early brain development, intrauterine disturbances, perinatal injuries, and other central nervous system disorders. Individuals with colpocephaly have various degrees of motor disabilities, visual defects, spasticity, and moderate to severe intellectual disability. No specific treatment for colpocephaly exists, but patients may undergo certain treatments to improve their motor function or intellectual disability. Symptoms
There are various symptoms of colpocephaly and patients can experience effects ranging from mild to severe. Some patients do not show most of the symptoms related to colpocephaly, such as psychomotor abnormalilities and agenesis of the corpus callosum. In some cases, signs appear later on in life and a significant number of children only develop minor disabilities. The following list includes common symptoms of colpocephaly. partial or complete agenesis of the corpus callosum
intellectual disability
motor abnormalities
visual defects such as, crossing of the eyes, missing visual fields, and optic nerve hypoplasia
spasticity
seizures
cerebral palsyIntracranial abnormalities include:

Microcephaly
Agenesis of the corpus callosum
Meningomyelocele
Lissencephaly
Periventricular leukomalacia (PVL)
Enlargement of the cisterna magna
Cerebellar hypoplasia

Causes
There is no known definitive single mechanism that causes colpocephaly. However, researchers believe there are many possible causes of colpocephaly.