Most typical kids will easily get interested in things if another person demonstrates an interest-- that social pull can drive the intellectual engagement. For an autistic person, the lack of interest can be in part due to a lack of social perspective-taking-- not being able to appreciate what the other person finds interesting.
DeeDee
I'm on the fence here. DeeDee my DS responds to that social pull that you mention, and he engages well,
when he's interested. I guess it depends on the child, and the type and frequency of these interactions.
(He just had two friends over, and they, he and DD all played happily together for a couple of hours).
In grade one, DS was screened for autism by the school's psychology intern. In her report, as evidence of "spectrum like behaviour," she mentioned that DS became withdrawn because no one would play chess with him. He tried to find someone to play with, and when he discovered no one else knew how, he decided to play alone. (They weren't clear in the report if he played chess alone or something else - but evidently he wasn't interested in whatever the other kids were doing).
Now I'm not saying DS isn't on the spectrum (because who really knows) but choosing solitude over playing something that bored him just for the sake of having a playmate doesn't necessarily put him on the spectrum.
At what point is a child NOT on the spectrum, but simply an introvert?