The Penn study, whose authors came from the university's Annenberg Public Policy Center and the Perelman School of Medicine, put labels to the test.
The researchers tested two kinds of warning labels: those featuring images judged to provoke a high emotional reaction, including the three listed above, as well as others that elicited a low emotional response. They also tested neutral images.
The scientists showed pairs of images to 25 smokers. The first was one of the high, low, or neutral variety. The second was called a smoking "cue," such as a person lighting a cigarette.
These cues had previously been shown to elicit a cigarette craving as well as a spike in brain activity thought to reflect unconscious attraction. These spikes were measured in an electroencephalogram (EEG).
But when the cues were preceded by one of the high-emotion, or "strong," warning labels, such as the one of the bloody lip sore, the spike in unconscious attraction was diminished. Not so with the low-emotion or neutral images.
The study, published online in the journal Addiction Biology, indicates the stronger labels could discourage people from lighting up, said Penn psychiatrist Daniel D. Langleben, one of the authors. "If you multiply that by 100 million, you have a health effect."
A stronger label "brings home the fact that this is a dangerous product much more successfully," said coauthor Dan Romer, an associate director for research at Annenberg.
The lead author of the study was An-Li Wang, a neuroscientist at Annenberg.
David Hammond, a University of Waterloo researcher who also has studied the impact of warning labels, said the Penn study helped demonstrate that the graphic images work.
Similar images already have helped cut the smoking rate in Canada, he said. "It starts to attach a different image to the product and the behavior than traditional associations of cool or sexy," Hammond said.