Stress increasesCue-Triggered “wanting” for Sweet Reward in Humans Forty-one participants, but only 36ended up participating in the research, who liked chocolate were asked toparticipate in this research. The researchers asked if they would refrain fromeating, practice, sport, or drink coffee four hours prior to the session. “The Pavlovian stimuli consisted onthree geometric complex figures typically used in human conditioning paradigmsthat in a pilot study were rated as similarly neutral on a pleasantness scale.
“(Pool, Brosch, Delplanque, Sander, p. 130) The mobilized effort was measuredthrough an isometric handgrip. The dynamic value of the signal read by MATLABand used to provide participants with visual online feedback that reflected theforce exerted on the handgrip. If the handgrip was squeezed with theparticipants maximum force with at least 50%-70% then the mercury of thethermometer would reach the top. Thefirst part of the experiment, the researchers had the participants complete theanalogous Pavlovian and instrumental conditioning. After those twoconditionings, but before the transfer test, 18 of the participants performedthe stress-induced task, and the other group performed a stress-free task.
After,they took a ten-minute break and thendid the PIT test, then evaluated the pleasantness of the odors. To trigger the releaseof the chocolate odor the participants learned to squeeze a handgrip trigger. Therewere 24 trials and each of them consisted of a 12-s “task-on” period followedby a “task-off” period with an 8s average. During the task-on periods, a geometricimage and a thermometer were shown in the center and left side of the screen. Theparticipants were asked to keep a closer eye on the central image and to squeezethe handgrip to bring the mercury to the maximum and then down again, withoutpaying attention to the speed of the grips. They were told that if they were tosqueeze the handgrip during the special 1s window it would trigger the releaseof the chocolate odor. After all they were told they could squeeze on the gripwhenever. Only two special 1s windows were randomly selected in the task onperiod to be rewarded with the odor of chocolate.
If the participants squeezedthe grip with at least 50% of maximal force a sniffling signal was displayed atthe center of the image and then the odor was released. While during thetask-off periods, a fixation cross was shown at the center of the screen andthe participants were asked to focus on that. For the researchers to controlthat participants assigned to the groups, stress and stress-free groups, tomake sure they did not statistically differ in their Pavlovian learning theyapplied five trials to the two groups. This analysis revealed a difference inthe average frequency for squeezes between the two groups and the participants thatwere in the stress-free group squeezed an average of 1.8 more than theparticipants in the stress group.