While the economic slump has many Americans tightening their belts, higher-income earners are feeling more optimistic and boosting their spending plans, a new survey finds.

Of more than 4,000 U.S. households recently surveyed by Changewave, a Rockville, Md.-based research firm, only 40 percent said they expected to reduce spending over the next three months, down from 42 percent in April. The gains in May were driven by an improved economic outlook among respondents earning more than $100,000, the firm reported.

By contrast, 61 percent of respondents who earned less than $50,000 said they planned to cut back in the months ahead, up from 55 percent.

The survey also found that inflation and rising energy prices were overtaking personal debt as the main reason consumers cited for spending less. In May, only a quarter of survey respondents said they were saving to pay off debts, compared to roughly half who said they were prompted by inflation or energy costs.