His robotic acting suited the character I felt.

I agree, I'm sorry, but this is bad acting, plain and simple. Lack wasn't a trained actor and it shows, but really, it's fine. It doesn't ruin the film, in my opinion at least.
I there have been plenty of great actors who've played androids and emotionless beings and pulled off good performances: John Malkovich, Leonard Nimoy, Douglas Rain as HAL 9000, Zachary Quinto as New Spock. Maybe the character is supposed to be emotionless, but the character's job is still to make the audience feel something. I think Lack's performance is just not evocative; it seems like he's overthinking the lack-of-emotion aspect of his character to an extent that doesn't feel natural.

Apparently Cronenberg cast him because of his unusual eyes, not his acting ability, unfortunately..
Was it a millionaire who said "Imagine no possessions"?

So you're denying Lack's character was a mentally disturbed, apparently homeless outcast and a misfit loner - in which case his strange awkwardness would be understandable?
"facts are stupid things" Ronald Reagan

i love how people have to explain that an actor's bad acting wasn't really bad acting, but just the character. OK, next someone explain Pauly Shore's bad acting in everything.

That Lack was not a trained actor and not totally dedicated to acting as a career is obvious. He made 10 movies total and one in the last 25 years.
But i also cannot defend his performance in Scanners as anything more than he was as perfect for the role as Ahnuld was for The Terminator. Lack's stunted, awkward, monotone delivery and odd body language could be excused for all the reasons other posters have commented on already - that he was a loner and outcast living on the periphery of society.
Or that maybe that's all he was capable of, and Cronenberg saw him as a perfect fit for the role of Cameron.

I really do not get all the hate for Lack's performance. I have seen the movie several times now (my first time was as a young teenager and my last time was last night) and I never had any damn problem with Lack's portrayal of the character. He is described from the get-go as a social misfit and eventually as an almost 'non-human',so the fact that he is barely expressive completely fits the role. Furthermore, I would add that for me, Lack was actually quite convincing in the role, especially when you see him being affected by his scanner abilities, and that the movie, which really holds up well still today for me, benefits from everybody's performances here. Of course, you could say that Michael Ironside, an actor I have always liked since Total Recall (I saw Scanners after that), steals the show in the movie, but I think the movie just would not work like it does if the acting was weak around him. Ironside had a sinister but more flashier role than basically everybody here except perhaps for the actor who was playing Benjamin Pierce, who was barely several minutes in the movie.
So for me, Lack does not even deserve to be nominated for a Razzie as his performance was on the money for the specific role that he had here.
Bill Foster: I'm the bad guy?How did that happen?

I don't know how much sense this makes, but even though his acting wasn't "good," it fit right in with the movie, for me. The overall off-kilter, surreal tone of the whole enterprise was actually enhanced by Lack's stoned, deer-in-headlights performance.
If Cronenberg had wanted an actorly, "professional" performance, I'm sure he could've found someone to deliver one.
Besides, I would reserve Razzies for actual actors. Lack's a painter that was in a few movies. I wouldn't give him a Razzie any more than I'd give Michael Jordan a Razzie for Space Jam.

I have meddled with the primal forces of nature and I will atone.

I agree, I've seen better acting in porn.

Your face is cringe worthy

Agreed.
THE ONLY CRITIC WHO CAN REVIEW WHILE JOGGING:
http://bit.ly/1pPzoBc

It's one of the worst performances ever captured on Film. It's embarrassing to see people actually defend it.

Yep, first awarded March 31, 1981, so Scanners would be up for the 1982 awards.
You need to account for the very likely possibility that the razzies were intended to shame big name people, not obscure actors appearing in low budget horror flicks like Stephen Lack. The razzies would never have become a name brand if every time the awards were announced 99.99% of the world said "Who?" Either the actor or the film has to come with higher expectations to be considered. Laurence Olivier got one in 1982. You get the idea.

This message has been deleted.

He talked the way you would expect, with lots of voices inside your head
good point, anyway was the razzie even around then?

This message has been deleted.

Or maybe it's a "delusion" to think that Cronenberg would have cast Lack or tolerated his delivery if it wasn't what he wanted?
"facts are stupid things" - Ronald Reagan

Can we please not delude ourselves into thinking his horrendously cringeworthy delivery was an ACTING CHOICE?! Whether it worked or not (which it didn't because none of the other actors playing Scanners talked like that!) it was horrible and very Razzie worthy.

it's explicitly mentioned that vale has been kept on ice. not so surprising that he'd be lacking in emotion.

"It's better not to know so much about what things mean." David Lynch

True, Stephen Lack's character seems very one-dimensional but, like other users here have pointed out, it suited his performance in the film. Remember that he was a street bum and an outcast, so having someone performing this character with more flair would look uncalled for.
Scanners is probably my favorite Cronenberg film. It has an air of eerieness that still holds today.

This message has been deleted.

I think his performance worked for the character, who was described as not ever having really developed his own personality. So his monotone delivery, lack of affect and general awkwardness seemed like a logical extension of that to me.

The acting is intentional, part of the character. Kim even goes as far as calling Cameron "barely human."