Tachistoscope

Cognitive scientists use a scientific instrument called a tachistoscope to show subjects an object, image, or passage of text, for a precise interval.

Inside a traditional tachistoscope there is typically a prism or mirror, at 45 degrees. Invisible to the subject, the device has two identical arms, at right angles to one another. the device is engineered so that only one arm is lit, at a time. se In some experimental designs the experimenter will learn whether the subject recognized the object from their verbal description. Or, they could be hooked up to sensors, like a galvanic skin response sensor. Or they could be asked to push a button if they recognized the subject, so, the experimenter can measure their reaction times.