Multi-tasking lowers productivity.What influences on attention cause the productivity of a multi-tasking person to be low?An example of multi-tasking is that a person is working on his assignment while trying to memorize unfamilar Spanish words.  
How is attention involved with the performance drop associated with multi-tasking?
cognitive psychology;performance;attention
One important factor to consider is whether the separate tasks involve the same kind of mental process. For instance, among these multi-tasking scenarios:listen to someone and read something at the same timelisten to someone and walkwalk and read something at the same time$\#1$ is generally harder than $\#2$, partly because both of its tasks involve linguistic processing, whereas walking does not. $\#2$ might be a somewhat unfair example at first glance, because walking is also more self-contained and automatic on flat ground. On uneven ground, however, $\#3$ would be much harder than $\#2$, because both walking and reading require visual processing in such circumstances. This point implicates automaticity and difficulty as (probably related) influential factors as well. I'm sure there are others, and I hope others will help fill in other ideas.