State revenue collections plunged by 6.5 percent in January, leaving lawmakers well behind their targets for the current year as they make deep cuts in the budget. Monthly receipts from taxes paid largely on investments and by the self-employed were down nearly 23 percent last month from January 2009. The weak showing was aggravated by corporate income tax refunds made in January this year but not until February last year. A small bright spot was a marginal increase in taxes withheld from paychecks. But a poor January leaves the state 4.7 percent behind where it was a year ago seven months into the fiscal year. That’s well below the estimated 2.7 percent decline on which the current budget is built.