 "Nonverbal learning disabilities" were further discussed by Myklebust in 1975 as representing a subtype of learning disability with a range of presentations involving "mainly visual cognitive processing," social imperception, a gap between higher verbal ability and lower performance IQ, as well as difficulty with handwriting.Later neuropsychologist Byron Rourke sought to develop consistent criteria with a theory and model of brain functioning that would establish NLD as a distinct syndrome (1989).Questions remain about how best to frame the perceptual, cognitive and motor issues associated with NLD.