Either is correct in the examples you gave, but it doesn't specifically have to do with using "such as. It has do with whether the word you're using is a definite article or not. In the example you gave I would prefer "such as reaction time" although "such as the reaction time" might be correct in some cases too. If you'd written "such as the White House" you'd need the 'the'. :-) If you'd need the definite article writing the word in a typical way, use it with such as also.