Stress the handgrip was squeezed with the participants maximum

Stress increases
Cue-Triggered “wanting” for Sweet Reward in Humans

            Forty-one participants, but only 36
ended up participating in the research, who liked chocolate were asked to
participate in this research. The researchers asked if they would refrain from
eating, practice, sport, or drink coffee four hours prior to the session. “The Pavlovian stimuli consisted on
three geometric complex figures typically used in human conditioning paradigms
that in a pilot study were rated as similarly neutral on a pleasantness scale.”
(Pool, Brosch, Delplanque, Sander, p. 130) The mobilized effort was measured
through an isometric handgrip. The dynamic value of the signal read by MATLAB
and used to provide participants with visual online feedback that reflected the
force exerted on the handgrip. If the handgrip was squeezed with the
participants maximum force with at least 50%-70% then the mercury of the
thermometer would reach the top.

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            The
first part of the experiment, the researchers had the participants complete the
analogous Pavlovian and instrumental conditioning. After those two
conditionings, but before the transfer test, 18 of the participants performed
the stress-induced task, and the other group performed a stress-free task. After,
they took a ten-minute break    and then
did the PIT test, then evaluated the pleasantness of the odors. To trigger the   release
of the chocolate odor the participants learned to squeeze a handgrip trigger. There
were 24 trials and each of them consisted of a 12-s “task-on” period followed
by a “task-off” period with an 8s average. During the task-on periods, a geometric
image and a thermometer were shown in the center and left side of the screen. The
participants were asked to keep a closer eye on the central image and to squeeze
the handgrip to bring the mercury to the maximum and then down again, without
paying attention to the speed of the grips. They were told that if they were to
squeeze the handgrip during the special 1s window it would trigger the release
of the chocolate odor. After all they were told they could squeeze on the grip
whenever. Only two special 1s windows were randomly selected in the task on
period to be rewarded with the odor of chocolate. If the participants squeezed
the grip with at least 50% of maximal force a sniffling signal was displayed at
the center of the image and then the odor was released. While during the
task-off periods, a fixation cross was shown at the center of the screen and
the participants were asked to focus on that. For the researchers to control
that participants assigned to the groups, stress and stress-free groups, to
make sure they did not statistically differ in their Pavlovian learning they
applied five trials to the two groups. This analysis revealed a difference in
the average frequency for squeezes between the two groups and the participants that
were in the stress-free group squeezed an average of 1.8 more than the
participants in the stress group.