Go-nogo categorization and detection task

Participants seated in a dimly lit room at 110 cm from a computer screen piloted from a PC computer. Two tasks alternated: a categorization task and a recognition task. In both tasks, target images and non-target images were equally likely presented. Participants were tested in two recording phases. The first day was composed of 13 series, the second day of 12 series, with 100 images per series (see details of the series below). To start a series, subjects had to press a touch-sensitive button. A small fixation point (smaller than 0.1 degree of visual angle) was drawn in the middle of a black screen. Then, an 8 bit color vertical photograph (256 pixels wide by 384 pixels high which roughly correspond to 4.5 degree of visual angle in width and 6.5 degree in height) was flashed for 20 ms (2 frames of a 100 Hz SVGA screen) using a programmable graphic board (VSG 2.1, Cambridge Research Systems). This short presentation time avoid that subjects use exploratory eye movement to respond. Participants gave their responses following a go/nogo paradigm. For each target, they had to lift their finger from the button as quickly and accurately as possible (releasing the button restored a focused light beam between an optic fiber led and its receiver; the response latency of this apparatus was under 1 ms). Participants were given 1000 ms to respond, after what any response was considered as a nogo response. The stimulus onset asynchrony (SOA) was 2000 ms plus or minus a random delay of 200 ms. For each distractor, participants had to keep pressing the button during at least 1000 ms (nogo response).

More specifically, in the animal categorization task, participants had to respond whenever there was an animal in the picture. In the recognition task, the session started with a learning phase. A probe image was flashed 15 times during 20 ms intermixed with two presentations of 1000 ms after the fifth and the tenth flashes, allowing an ocular exploration of the image; with an inter-stimulus of 1000 ms. Participants were instructed to carefully examine and learn the probe image in order to recognize it in the following series. The test phase started immediately after the learning phase. The probe image constituted the unique target of the series. Both tasks were organized in series of 100 images; 50 targets images were mixed with 50 non-targets in the animal categorization task; 50 copies of an unique photographs were mixed at random with 50 non-targets in the recognition task.

参与者坐在光线昏暗的房间内，距个人电脑操控的计算机屏幕110厘米处。实验包含两类交替进行的任务：分类任务与再认任务。两类任务中，目标图像与非目标图像的呈现概率均等。参与者需在两个测试阶段完成实验：第一日包含13组实验序列，第二日包含12组，每组序列含100张图像（序列详细说明见下文）。
启动一组序列时，受试者需按压触控按钮。黑色屏幕中央会呈现一个小型注视点（视角小于0.1度）。随后，一张8位彩色立式照片（宽256像素、高384像素，对应视角宽约4.5度、高约6.5度）通过可编程图形卡（VSG 2.1，剑桥研究系统公司（Cambridge Research Systems））以20毫秒的时长呈现（对应100Hz SVGA屏幕的2帧）。该极短呈现时长可避免受试者通过探索性眼动做出反应。
参与者采用go/nogo范式（go/nogo paradigm）进行反应：对于每张目标图像，受试者需尽可能快速且精准地抬起手指离开按钮（松开按钮会触发光纤发光二极管（LED）与其接收器之间的聚焦光束，该设备的响应潜伏期低于1毫秒）。参与者有1000毫秒的反应时限，超时未作出反应则视为nogo反应。刺激呈现间隔（stimulus onset asynchrony，SOA）为2000毫秒±200毫秒的随机偏移。对于每张干扰项（distractor），受试者需持续按压按钮至少1000毫秒，该操作即为nogo反应。

具体而言，在动物分类任务中，受试者需在图片中出现动物时作出反应。
在再认任务中，实验会话首先进入学习阶段：探测图像会以20毫秒的时长呈现15次，其中在第5次和第10次呈现后，会分别以1000毫秒的时长各呈现一次，以供受试者对图像进行视觉探索；刺激间间隔为1000毫秒。受试者需仔细观察并记住该探测图像，以便在后续序列中完成再认。学习阶段结束后立即进入测试阶段，该探测图像即为该组序列的唯一目标图像。
两类任务均以100张图像为一组序列：动物分类任务中，50张目标图像与50张非目标图像随机混合；再认任务中，50张完全相同的目标照片与50张非目标图像随机混合。