authors usually change the font ( type or lettering) for emphasis.
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I wasnt able to discover anything on a "font change," but I did find an interesting tid bit on the font that was used;
The Curious Incident of the Dog in the Night-Time uses a sans serif font: that is, a simple kind of print in which letters lack the little tails and plinths that printers call serifs. This is highly unusual in any published book; the conventional wisdom is that serifs help the brain's visual apparatus as a line of print is scanned. The tiny thickenings and thinnings of the limbs of every letter give the eye something to catch on to. Sans serif fonts may be used in advertisements, headlines and the like, but their simplicity is almost physically uncomfortable in any lengthy text.
The font's discomfiting simplicity is perfectly suited to Haddon's narrator, Christopher, in all his pedantic veracity. He narrates plainly (sometimes just cataloguing or enumerating) and the plainness is even there in the lettering. Reading a page printed like this is, I think, visually disconcerting. Graphically speaking, we are in Christopher's nuance-free world from the start. We are unsettled by its lack of variation, just as we will become conscious of his flat-voiced failure to sense the emotions and tones of the novel's other characters.