John Ross, chief executive of Shopper Sciences, a marketing research company that is part of the Interpublic Group, said Affectiva’s technology promises to give marketers an impartial reading of the sequence of emotions that leads to a purchase, in a way that focus groups and customer surveys cannot. “You can see and analyze how people are reacting in real time, not what they are saying later, when they are often trying to be polite,” he said. The technology, he added, is more scientific and less costly than having humans look at store surveillance videos, which some retailers do.