Emotion Category and Face Perception Task Optimized for Multivariate Pattern Analysis
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## 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).
我们招募了16名男女混合的横断面研究受试者（8名女性，8名男性），平均年龄25岁，于2019年10月至2020年6月期间在墨西哥国立自治大学（Universidad Nacional Autónoma de México, UNAM）胡里基拉校区完成招募。首先对受试者进行简短访谈，排除既往确诊神经系统或精神疾病者。除1名男性受试者外，其余均报告为右利手表型。本研究开展前，已向所有受试者告知研究目的、风险与操作流程，受试者签署正式知情同意书后方可参与，本研究符合1964年《赫尔辛基宣言》的伦理规范。 ## 图像采集 所有受试者单次扫描即可完成图像采集，扫描设备为墨西哥国立自治大学神经生物学研究所磁共振成像单元的3-Tesla通用电气（General Electric, GE）Discovery MR750扫描仪。扫描方案包含5次回波平面成像（echo-planar imaging, EPI）血氧水平依赖（blood-oxygen level-dependent, BOLD）序列用于功能磁共振成像（functional Magnetic Resonance Imaging, fMRI），每个序列包含185层容积。此外还采集了头部解剖结构的T1加权扫描，以及任务开始前10分钟的静息态fMRI扫描。各序列参数详见下表。扫描过程中使用头戴式32通道线圈进行信号采集。 | 参数 | EPI BOLD | T1w FSPGR | T2w FSE | |----------------|--------------:|-----------------:|------------:| | 扫描层面方向 | 轴位 | 轴位或矢状位 | 轴位 | | 层面数量 | 35 | 176 | 35 | | 视野 | 64×64 | 256×256 | 512×512 | | 体素尺寸 | (4 mm)³ | (1 mm)³ | (0.5×0.5×0.4 mm³) | | 翻转角度 | π/2 | 3π/45 | 7π/9 | | 重复时间（ms） | 2000 | 8.18 | 6255 | | 回波时间（ms） | 30 | 3.19 | 101.4 | | 反转时间（ms） | | 450 | | ## 刺激与任务 本研究的5次fMRI序列均与基于任务块（block）的心理范式在时间上同步，任务范式采用PsychoPy 3.0.1编写。5次任务范式完全一致，仅30秒的任务块施予顺序采用伪随机排列。本次研究共使用6类任务块：快乐面部表情、悲伤面部表情、愤怒面部表情、中性面部表情、伪面孔（打乱重组的面孔）以及低刺激（昏暗）条件。 设置伪面孔与昏暗条件任务块的目的是辅助验证分析流程，可通过更简单的对比（如伪面孔vs低刺激条件、面孔vs伪面孔）来校验分析流程。 每个任务块包含10张该类别下随机呈现的图像，每张图像呈现时长约3秒，且同一任务块内不会重复呈现同一张图像。每个任务块在每个序列中出现2次，总计12个任务块（总时长360秒，即6分钟）。所有刺激呈现结束后，受试者需等待10秒以采集末次刺激诱发的血流动力学反应（hemodynamic response, HR）。本研究选用的刺激为每类正面人脸灰度照片各10张（包含男性与女性面孔），这些图片选自经典的“面部表情图片库”（Pictures of Facial Affect, Ekman, 1976）。至于低刺激（又称“昏暗”）条件任务块，会呈现一个小而清晰的固定十字，每3秒随机在四个象限间切换位置。 此外，本研究全程记录行为学反应以评估任务表现，进而验证生理数据是否适用于后续分析。每次序列开始前，受试者会被要求在看到面孔时尽快判断面孔属于男性还是女性，通过双手各一个按键提交反应。对于无面孔呈现的打乱面孔与昏暗条件任务块，受试者的任务为仅报告图像变化，通过交替按动按键完成。 任务文件与反应数据可在[此处](https://github.com/isacdaavid/emotional-faces-psychopy-task)获取。
