The results of an independent-measures research study are reported as "t (22) = 2.12, p <.05, two tails." for this study, what t values formed the boundaries for the critical region?

As the level of significance here is 0.05 because we are comparing the p-value with 0.05. Therefore the critical region boundaries here would be given as:

For 5 degrees of freedom, we get: (from the t-distribution tables)

P (t_5 < 2.571) = 0.975

Therefore due to symmetry, we get:

P (-2.571 < t_5 < 2.571) = 0.95

Therefore the critical region here would be given as: + 2.571 and - 2.571