Many of you, I am sure, are perfectly familiar with the common speech feature known as de-alveolar assimilation. As its name suggests, this affects alveolar consonants, especially the stops t d n. After it has taken effect, an expected alveolar turns up as a consonant at some other place of articulation, typically bilabial or velar. So, for example, ten boys may be pronounced as tem bɔɪz and good girl as ɡʊɡ ɡɜːl. The following consonant in these examples has imposed its place of articulation on the preceding alveolar.
However, there are other sorts of assimilation which rarely make it into textbooks on English phonetics. One of these appears to be a favourite of Fiona Bruce, a British broadcaster, whom you can see in the picture above. In one recent edition of the BBC’s News at Ten, Ms Bruce uttered the word something as sʌn̪θɪŋ and himself as hɪnself. Here it is a bilabial consonant which is being influenced by the place of articulation of the following consonant: dental in the first example and alveolar in the second.
The motivation for all of these place changes is of course to cut down on articulatory movement. I am sure Fiona Bruce is not the only speaker to use this rarer (?) form of assimilation, but she does seem to do it fairly frequently.