Editing Stuttering (section)

===History of causes===

Auditory processing deficits were proposed as a cause of stuttering due to differences in stuttering for deaf or Hard of Hearing individuals, as well as the impact of auditory feedback machines on some stuttering cases.<ref>{{harvnb|Ward|2006|pp= 46–58}}</ref>

Some possibilities of linguistic processing between people who stutter and people who do not has been proposed.<ref>{{harvnb|Ward|2006|p= 43}}</ref> Brain scans of adult stutterers have found greater activation of the right hemisphere, than of the left hemisphere, which is associated with speech. In addition, reduced activation in the left auditory cortex has been observed.<ref name="gordon"/>

The 'capacities and demands model' has been proposed to account for the heterogeneity of the disorder. Speech performance varies depending on the 'capacity' that the individual has for producing fluent speech, and the 'demands' placed upon the person by the speaking situation. Demands may be increased by internal factors or inadequate language skills or external factors. In stuttering, severity often increases when demands placed on the person's speech and language system increase.<ref>{{harvnb|Ward|2006|pp= 16–21}}</ref> However, the precise nature of the capacity or incapacity has not been delineated. Stress, or demands, can impact many disorders without being a cause.

Another theory has been that adults who stutter have elevated levels of the neurotransmitter [[dopamine]].<ref name=":4"/><ref name="watkins">{{cite journal |last1=Watkins |first1=K. E. |last2=Smith |first2=S. M. |last3=Davis |first3=S. |last4=Howell |first4=P. |title=Structural and functional abnormalities of the motor system in developmental stuttering |journal=Brain |date=3 December 2007 |volume=131 |issue=1 |pages=50–59 |doi=10.1093/brain/awm241 |pmid=17928317 |pmc=2492392 }}</ref> 

It was once thought that forcing a left-handed student to write with their right-hand caused stuttering due to [[bias against left-handed people]], but this myth died out.<ref>{{cite journal |last1=Lewis |first1=Ruth |title=The psychological approach to the preschool stutterer |journal=Canadian Medical Association Journal |date=May 1949 |volume=60 |issue=5 |pages=497–500 |pmid=18125462 |pmc=1591462 }}</ref><ref>{{cite journal |last1=Bryngelson |first1=Bryng |last2=Clark |first2=Thomas B |title=Left-Handedness and Stuttering |journal=Journal of Heredity |date=October 1933 |volume=24 |issue=10 |pages=387–390 |doi=10.1093/oxfordjournals.jhered.a103681 }}</ref><ref>{{cite journal |last1=Johnson |first1=Wendell |last2=Duke |first2=Lucile |title=Changes in Handedness Associated with Onset or Disappearance of Stuttering: Sixteen Cases |journal=The Journal of Experimental Education |date=December 1935 |volume=4 |issue=2 |pages=112–132 |doi=10.1080/00220973.1935.11010003 }}</ref>