EFFECTS OF MIDLINE CROSSING ON RESPONSE PROCESSING OF ADULTS WITH MENTAL-RETARDATION

In normal development, midline crossing inhibition (MCI) generally dis appears by age nine. Individuals with mental retardation exhibit devel opmental delays which are manifested as failure to attain motor milest ones. This study utilized a new methodology predicted upon a response processing model to measure MCI in 20 adults with moderate mental reta rdation. A chronologically equivalent group of individuals with mental retardation served as the control group. Measurements of reaction tim e (RT) and movement time were recorded as a subject performed ipsilate ral, midline and contra-lateral movements. The rationale behind this e xperiment was that crossing midline to the contralateral side constitu ted a more complex task, requiring more response processing time and l onger RTs. Analysis of the RT revealed inhibitory responses in the sub jects with mental retardation when movements were made in a contralate ral direction with the preferred hand. No inhibition was manifested by the subjects in the control group. This new method of assessing MCI d etected this phenomenon with subjects who were mentally retarded.