Sign languages make working of metaphor clearer

I'm not sure that this is as big a break-through as it seems to be written up here, though it is certainly interesting to me as a linguist. But the phenomenon described is familiar to most of us who have worked on translations or been tripped up by a literal interpreting of a metaphor only to realise that a certain sense/shade of meaning doesn't map between the most natural choices in source and target languages. Check out the summary article here: Sign languages help us understand the nature of metaphors.
"This study shows that the iconicity of a form may constrain the possible metaphorical extensions that the form might take. Put another way, certain metaphorical expressions in spoken language cannot be 'translated directly' into sign language if their form is iconic."
And if that seems a bit opaque to you then perhaps the 'for instance' will clarify. I think it's interesting. The newer thing is the way that the performance of a ASL or (in this case) ISL sign constrains the connotative meaning and so what is available in terms of extended meanings available to remap in metaphoric usage.
"it is impossible to use the sign FLY (in Israeli Sign Language and American Sign Language) in the expression "time flies" or "the day just flew by." The metaphorical uses of a word such as FLY are impossible because of the form of this sign, in particular, its iconicity. The sign for FLY is produced by moving the arms as if flapping one's wings. But in the expression "time flies," we do not mean that time is flapping its wings. Rather, the metaphor is built on an implication of the action of flying, namely that it is a very fast way of motion. So there is a clash between what the form of the sign encodes (wing flapping) and the aspect of meaning on which the metaphor is built (fast movement)."
However, we should also recall the probable truth of the thesis in 'Metaphors we Live by' and 'Philosophy made Flesh' (Lakoff and Johnson in both cases) that much language is rooted in fundamental metaphors based on bodily experience (and making neurological links co-opting the relevant neuronal gestalts of somatic experience which does seem to be borne out in emerging brain imaging research). We should note it is the role of iconicity that is being picked out here. This is telling us something about (to use the vocabulary of another school in semiotics) motivated signs and their availability for metaphorical usage. What would be interesting to place beside this would be to look at the way that the FLY signs are pressed into metaphorical usage; what are the salient connotative meanings that can be drawn from the signs that can, in turn, be pressed into extended usage. I'm aware that SLs would be fascinating to look at from this kind of linguistic point of view. I hope one day I may have a chance to find out more.