A recent study at the University of Kyoto found that people had greater difficulty matching nouns to verbs when they were maintaining simulated eye contact than when they were looking at a face whose eyes were not directed at them.
The findings only held true when the noun-to-verb matches were considered difficult, i.e., the associations between a noun and verb were not terribly obvious, but there were also many options to choose from. (Science of Us, which publicized the study, gives the example of the sometimes-noun "list;" one can "check," "make," or "write" a list, and so the brain does not know instantly which verb to recall as the most relevant.) This perhaps implies that eye contact makes more complex or general cognitive tasks difficult, although it may not interfere with simpler domain-specific ones according to Christian Jarrett of BPS Research Digest, quoted in the Science of Us article. For psychologists, the findings may be relevant in the context of patient interviews.