Back then it was all optical effects - the artists used lighting tricks and processed the film in different ways, then spliced the images together.
Something of a hijack, or at least a digression, but I’m not sure we can say for sure that all the effects in this impressive (and enjoyable) video were achieved using optical effects techniques.
According to the internet, this single was released in September 1980. We would expect that the video was produced around the same time, although it’s faintly possible that the video was born a little later (sometimes in the recording industry, it’s song first, then video, and there can be quite a gap). Quantel was the first company to develop systems for applying digital effects to television signals. Prior to 1980, their only commercially released product was a digital framestore, i.e a way of producing a ‘freeze frame’ during live television (younger readers will be startled to learn that this was once considered a great achievement). Their ‘Paintbox’ product, which introduced ‘squeeze zoom’ and a host of other new digital effects, thereby revolutionising the TV industry, was not officially / commercially released until 1981. However, it is entirely likely that some production companies and broadcasters had access to ‘pre-release’ version of ‘Paintbox’ (Quantel would have made pre-release or ‘beta’ versions available so that, when launching the product, they already had examples of what their product could do). If this is the case, then someone working on the ‘Can You Feel It?’ video may well have had access to ‘Paintbox’ technology.
I only mention all of this because, on first viewing, it would seem difficult to achieve all of the effects in the video just using optical effects. There are a few touches here and there that look to me as if they would have needed the benefit of early digital effects, such as provided by the Quantel Paintbox system.
Just in case you were wondering, I worked in video production during these years, back when video was new and exciting, and so I had a good look at each step in the evolution of digital effects and their impact on the TV industry.