Participants were asked to rate pictures on pain intensity. The instruction was as follows:
Pain rating task
Please read the instructions carefully.
In this study we ask you to rate PICTURES on pain intensity. These pictures are single screenshots taken from movies, that show two different events:
Face events: of a person receiving electrical shocks to the hand
Hand events: of a person receiving slaps with a belt on the hand
You will first view 8 example movies to get a sense of how the two different events look like. The movies will have different intensities of pain stimulations.
Because every movie is real we never did stimulations of 10 or 9, as this would be unethical. The maximum stimulation given in the movies is 7 or 8. It is important to know however that the person in the movies always receives a stimulation.
First participants were introduced to the movies from which the frames were taken. 8 videos were shown: 2 low pain face videos, 2 high pain face videos, 2 low pain hand videos and 2 high pain hand videos. Participants only had to observe.
Practice
Next, participants could practice rating 4 frames. The instruction was as follows:
From these types of movies we have taken single screenshots. See 4 example pictures below.
During the actual task you will be shown similar pictures like these that were taken from movies. We would like to know if it is still possible to rate the pain intensity if you can only view 1 screenshot instead of the whole movie. Be aware, that it is not always easy to do this! Even if you feel you cannot rate the intensity from the picture, please still do so.
The pictures will be shown for 2 seconds, after which you are asked to rate the intensity of the pain the person is feeling.
The rating is on a scale from 1 to 10, where 1 means no pain and 10 means the most intense pain imaginable.
and remember because every picture is real (coming from a real movie) we never did stimulations of 10 or 9, as this would be unethical. The maximum stimulation given in the pictures is 7 or 8. It is important to know however that the person in the pictures always receives a stimulation.
You will now first start with 4 practice trials.
Trial
Then the actual experiment started. Frames were shown for 2000 ms after which participants were asked to rate the frame.
A trial looked as follows:
Rating screen:
In between, participants had to rate their attention 2 times and could take a break 1 time for 1 minute.
Readers should cite both the Bio-protocol preprint and the original research article where this protocol was used:
Soyman, E, Keysers, C and Gazzola, V(2024). Control participants in the online frame rating task. Bio-protocol Preprint. bio-protocol.org/prep2662.
Soyman, E., Bruls, R., Ioumpa, K., Müller-Pinzler, L., Gallo, S., Qin, C., van Straaten, E. C., Self, M. W., Peters, J. C., Possel, J. K., Onuki, Y., Baayen, J. C., Idema, S., Keysers, C. and Gazzola, V.(2022). Intracranial human recordings reveal association between neural activity and perceived intensity for the pain of others in the insula. eLife. DOI: 10.7554/eLife.75197
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