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Two-alternative forced choice (2AFC) (and the variant Two-interval forced choice (2IFC)) Task is a psychophysical method, developed by Gustav Theodor Fechner,〔 (Vol 2. )〕 for eliciting responses from a person about his or her experiences of a stimulus. Specifically, the 2AFC experimental design is commonly used to test speed and accuracy of choices between two alternatives given a timed interval. The task is an established controlled measure of choice and is widely used to test a range of choice behaviors in animals and in humans. The basic components of a 2AFC task are 1) two alternative choices presented simultaneously (e.g. two visual stimuli), 2) a delay interval to allow a response/choice, 3) a response indicating choice of one of the stimuli. ==Behavioural Experiments with 2AFC== There are various manipulations in the design of the task, engineered to test specific behavioral dynamics of choice. In one well known experiment of attention that examines the attentional shift, the Posner Cueing Task uses a 2AFC design to present two stimuli representing two given locations. In this design there is an arrow that cues which stimulus (location) to attend to. The person then has to make a response between the two stimuli (locations) when prompted. In animals, the 2AFC task has been used to test reinforcement probability learning, for example such as choices in pigeons after reinforcement of trials. A 2AFC task has also been designed to test decision making and the interaction of reward and probability learning in monkeys. Monkeys were trained to look at a center stimulus and were then presented with two salient stimuli side by side. A response can then be made in the form of a saccade to the left or to the right stimulus. A juice reward is then administered after each response. The amount of juice reward is then varied to modulate choice. In a different application, the 2AFC is designed to test discrimination of motion perception. The random dot motion coherence task, introduces a random dot kinetogram, with a percentage of net coherent motion distributed across the random dots. The percentage of dots moving together in a given direction determines the coherence of motion towards the direction. In most experiments, the participant must make a choice response between two directions of motion (e.g. up or down), usually indicated by a motor response such as a saccade or pressing a button. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Two-alternative forced choice」の詳細全文を読む スポンサード リンク
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