The use of icons is a fairly discussed issue here on UX.SE. I would suggest you read the answer from Michael Zuschlag in this post where he breaks down the problem very thoroughly.
Not having any scientific data to back me up I would still say that there are cases when the use of icons are much more usable than descriptive text. And I'm not talking about the floppy disk icon for Save. Although that is a recognized pictogram for the action Save, it doesn't really touch the cases I want to discuss.
Icons are a great tool when the icon itself helps the user understand its meaning better than a descriptive text would. A perfect example of this is the use of icons to represent the styling/formatting of text in text editors.
As far as I'm concerned these three icons do a much better job than three buttons saying
download bmml source – Wireframes created with Balsamiq Mockups
So why are they better? Well, the icons clearly show what will happen to the text when the user triggers them, in a way that the descriptive text doesn't. This will reduce the cognitive load as the user won't have to scan the GUI and translate the semantic meaning of the terms, the icon does it for them!
In addition to this the users that are unaware of the English terms for these options will find much aid in finding the correct action using the icons, and thereby having the cognitive load and time form trial and error reduced.
There is generally, in my mind, a too much "that will do" mindset when choosing an icon over descriptive text. The justification according to the designer is that the GUI will "look better" and "be more streamlined". This is however purely a graphic designer/artist approach and will in most cases not be suitable usability wise.
A good example is this post where the OP wants to find an icon that describes Factory reset instead of using the descriptive words "Factory reset".
Where the most popular answer provided is:
And sure, when playing Pictionary this illustration would be very nifty and some of the contenders would probably get it (I must admit I would struggle with it though). But were not playing Pictionary, are we... And Roger, the answerer, clearly states that the icon should be combined with clear labelling that clarifies that "This icon represents the action Factory reset". Rendering the icon redundant.
In summary, use icons when you can clearly justify that the icon will convey the action more clearly than a descriptive text will.