Both candidates have seen their image ratings affected by contentious, televised debates and negative advertising. Brown is viewed favorably by 52 percent and unfavorably by 36 percent, a net-negative change of 6 percentage points. Warren's negatives are rising faster. The Harvard Law School professor who helped set up a new consumer-protection agency for the federal government is now viewed favorably by 50 percent and unfavorably by 41 percent. Three weeks ago, 53 percent viewed her favorably, compared to 33 percent unfavorably. A majority, 55 percent, approve of the job Brown is doing in the Senate, but, by a wide margin, voters prefer Democrats control the Senate. Forty-eight percent of likely voters want to see the Senate remain in Democratic hands, compared to only 24 percent who want Republicans to take over. The poll is the fourth consecutive live-caller survey to show Warren with a narrow lead. The other three -- conducted in late September -- showed Warren ahead by between 4 and 5 points. The poll was conducted Sept. 28-Oct. 4, surveying 440 likely voters via landline and cell phones. The margin of error is plus-or-minus 4.7 percentage points.