Abstract: In a device to test a person's attention or concentration ability, a series of digits is read out at a pre-determined, alterable speed by a speech recorder (62) and delivered by a speech generator (66) to headphones (10). The subject must press a button (16) every time a target (e.g. "0") is heard. Also every time a "0" is heard, a control unit (50) produces a window signal which is connected by an error logic circuit (70) to the key-press impulse. If the reaction is correct, the key-press impulse will be within the time window, and a counter (74) will accordingly increase the number of the "score". Any key-press impulse falling outside the time window is an omission error to be counted by another counter (75). The counter status is then analyzed to calculate an error index (I.sup.E).