Stimuli and measures
NRS, Pain, pain
When carrying out an experiment focused on color, significant elements are the participants’ color perception and the screen which displays the colors. The former was assessed via the Ishihara test during the screening phaseTo measure the effect of colors on pain perception, we used 6 different color hues: red (RGB (255, 0, 0)), green (RGB (0, 255, 0)), orange (RGB (255, 128, 0)), blue (RGB (0, 128, 255)), yellow (RGB (255, 255, 0)), and pink (RGB (255, 0, 128)). The colors were selected in such a way to examine primary and complementary colors. The saturation level was set at 100%, because the hues are most distinct at this levelEach group received pain stimuli of one modality: either electrical or thermal. Pain stimuli were delivered to the volar side of the non-dominant forearm within C5 dermatome (participants self-reported handedness). Electrical stimuli (Digitimer DS8R; Digitimer; Welwyn, Garden City, England) were square pulses applied in a sequence of three pulses (200 μs) with an ISI of 100 μs. Thermal stimuli were applied using a contact thermode, sized 30 × 30 mm (Model ATS and TSA-II; Medoc Ltd Advanced Medical System; Israel), starting from a 32 °C baseline temperature with a 10 °C/s ramp-up/ramp-down ratio and 1 s plateau. To achieve the best possible similarity in pain sensation evoked with thermal and electrical stimulation, the physical characteristics of the stimuli (i.e. duration) were adjusted and calibration procedure was applied.Participants rated pain intensity (“How painful was the stimulation?”) and pain expectation (“How painful do you expect the stimulation to be after seeing this color?”) separately on an 11-point Numeric Rating Scale (NRS), from 0 = ‘no pain’ to 10 = ‘the most intense tolerable pain’. The NRSs were always presented on a color slide corresponding to the color used in the current trial.The procedure was programmed using Python 3 language and PsychoPy 2021 software