What is the test for determining whether a person has a severe impairment that limits their ability to do basic work activities?

First, the Commissioner considers whether the claimant is currently engaged in substantial gainful activity. If he is not, the Commissioner next considers whether the claimant has a severe impairment which significantly limits his physical or mental ability to do basic work activities. If the claimant suffers such an impairment, the third inquiry is whether, based solely on medical evidence, the claimant has an impairment which is listed in Appendix 1 of the regulations. If the claimant has such an impairment, the Commissioner will consider him disabled without considering vocational factors such as age, education, and work experience.... Assuming the claimant does not have a listed impairment, the fourth inquiry is whether, despite the claimant's severe impairment, he has the residual functional capacity to perform his past work. Finally, if the claimant is unable to perform his past work, the Commissioner then determines whether there is other work which the claimant could perform.

DeChirico v. Callahan, 134 F.3d 1177, 117980 (2d Cir.1998) (internal quotation marks and brackets omitted).