I took courses in socio- and psyco- linguistics, but I have never seen both terms together. The closest I could find was this term, which you can google and find some hits, such as

http://edrev.asu.edu/brief/nov05.html

I know the order of three words, 言語、社会、心理　are different in the traslation, but I do not think there is "lingpsychology", let alone "lingsociopsychology" in the dictionary.

You might also want to split the word, if that makes the meaning better understood, and/or for easy clarification, such as "in both sociolinguistic and psycolinguistic approach", "approach in linguistics and sociophycology".... Indeed, I might go for that.



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Note added at 9 hrs (2007-01-08 03:08:23 GMT)
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nothing significant, but I guess I like the "separation" of socio and psyco as suggested by Wil. Also, I said something incorrect as part of my response - Psycholinguistics is somewhat closer to cognitive linguistics, not neuroL. Snowbee-san's note reminded me of that... It's been over 15 years since I left school ;-) hehe.