## Sample We used a cross-sectional group of 16 volunteers from both sexes (8 female, 8 male) with an average age of 25 years, recruited at UNAM campus Juriquilla from October 2019 to June 2020. Participants were briefly interviewed to exclude those previously diagnosed with neurological or psychiatric conditions. With the exception of one male subject, all of them reported having right-handed phenotype. Prior to the study, subjects formally consented to participating after being informed of its aims, risks and procedures — in accordance with the 1964 Declaration of Helsinki. ## Image acquisition Images were obtained from a 3-Tesla General Electric Discovery MR750 scanner at the MR Unit at UNAM's Institute of Neurobiology, during a single session per participant. The protocol included 5 echo-planar imaging (EPI) blood-oxygen level-dependent (BOLD) sequences for fMRI, 185 volumes each. A T1-weighted scan of head anatomy was also acquired, in addition to a 10-minutes long _resting state_ fMRI before the task. Sequence parameters are described in the table. Echos were registered using a head-mounted 32-channel coil. | Parameter | EPI BOLD | T1w FSPGR | T2w FSE | |----------------|--------------:|-----------------:|------------:| | Slice orientation | Axial | Axial or sagital | Axial | | Slices | 35 | 176 | 35 | | Field of view | 64×64 | 256×256 | 512x512 | | Voxel size | (4 mm)^3 | (1 mm)^3 | (.5x.5x.4 mm^3) | | Flip angle | pi / 2 | 3*pi / 45 | 7*pi / 9 | | TR (ms) | 2000 | 8.18 | 6255 | | TE (ms) | 30 | 3.19 | 101.4 | | TInv (ms) | | 450 | | ## Stimuli and task Each of the 5 fMRI sequences was temporally coupled to a psychological block-based task implemented in PsychoPy 3.0.1. All 5 tasks were identical, save for the pseudo-random order in which their 30 s blocks were administered. A total of 6 block classes were used: happy faces, sad faces, angry faces, neutral faces, pseudo (scrambled) faces and low-stimulation (dim). Pseudo-faces and dim blocks were introduced so as to buttress and diagnose the analysis pipeline, by way of more trivial contrasts (like pseudo-faces vs low-stimulation and faces vs pseudo-faces). Each block in turn comprises 10 randomly-presented images belonging to that class, each one shown for about 3 seconds and without possibility of reinstantiation during the same block. Each block occurs twice per sequence, yielding a total of 12 of them (360 s = 6 min). After their presentation, participants had to wait for 10 seconds before concluding the sequence, in order to capture the hemodynamic response (HR) elicited by the last stimuli. A selection of 10 grayscale photographs per category of frontal human faces (male and female) served as stimuli. These were chosen from the classical "Pictures of Facial Affect" database (Ekman, 1976). As for the low-stimulation (a.k.a. "dim") blocks, a small but visible fixation cross was made fluctuate from quadrant to quadrant at random every 3 seconds. Additionally, behavioral responses were recorded throughout the task in order to measure performance and thus evaluate the suitability of physiological data for further analysis. Participants were instructed at the beginning of every sequence to indicate whether faces belonged to a man or a woman as soon as they were perceived. The response was submitted with the press of a button — one at each hand. Analogously, for scrambled and dim blocks (when no faces should have been perceived), the instruction was to simply report image change, alternating between buttons. Task files and responses available [here](https://github.com/isacdaavid/emotional-faces-psychopy-task).