In order to establish initial and continued entitlement to disability benefits under the Social Security Act (Act), a worker must demonstrate that, inter alia, he is unable "to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairment . . . ." The worker bears the continuing burden of showing, by means of "medically acceptable . . . techniques" that his impairment is of such severity that he cannot perform his previous work or any other kind of gainful work. A state agency makes the continuing assessment of the workers eligibility for benefits, obtaining information from the worker and his sources of medical treatment. The agency may arrange for an independent medical examination to resolve conflicting information. If the agencys tentative assessment of the beneficiarys condition differs from his own, the beneficiary is informed that his benefits may be terminated, is provided a summary of the evidence, and afforded an opportunity to review the agencys evidence. The state agency then makes a fi