Let's say a research assistant has provided help on conducting a literature review and that some of the references are eventually used in a published paper. Would the research assistant normally get some kind of acknowledgment or authorship if they did not contribute any written material?
I think you should definitely mention the research assistant in your acknowledgements, but not as an author. For such questions, I generally refer to the Vancouver Protocol, a widely used standard to determine appropriate authorship (search "Vancouver authorship" on the Web and you'll see that it is fairly well known):
The ICMJE recommends that authorship be based on the following 4 criteria:
- Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work; AND
- Drafting the work or revising it critically for important intellectual content; AND
- Final approval of the version to be published; AND
- Agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
Contributors who meet fewer than all 4 of the above criteria for authorship should not be listed as authors, but they should be acknowledged.
So, according to these principles, the research assistant is not a coauthor, but ought to be acknowledged.
Also, please note that coauthorship is often considered an ethical issue (that is, it is considered unethical to include someone who does not merit authorship, or to exclude someone who does), whereas it is more of a professional courtesy to acknowledge someone's contributions (that is, it is nice and collegial to acknowledge someone, but it is not considered unethical not to do so).