Abstract: The working quality of the human brain is measured with this method and apparatus by determining the highest frequency at which a subject can discriminate between synchronous and asynchronous pairs of two simultaneously presented periodic non-verbal stimuli: the higher this frequency (synchronism threshold) is the faster the brain of the subject can process information using the sensory function tested. The periodic stimuli provided to the subject and preceded by appropriate mask stimuli may be pairs of visual, tactile, electrocutaneous, and/or auditory stimuli within the same sense modality, or intermodal between two different senses. The apparatus generates the stimuli and indicates the nominal frequencies of the stimuli and threshold. The frequency threshold is determined by means of an adaptive staircase procedure in which the frequency is decreased after wrong responses and increased after correct responses.