An optical device for in vivo, non-invasive measurement of changes in hemoglobin concentration associated with activities of the cerebral function is provided. The device comprises a light source and a light detector (12) for irradiating light into a living body (11) and detecting scattered light having passed through the living body, a stimulus device (15) to intermittently present a stimulus to the subject and a noise detection system to detect noise associated with body movement of the subject from the detected scattered light signal. If body movement is detected during a measurement period the detected signal is discarded from further processing and a feedback is given to the stimulus device to repeat or adapt the presentation of the stimulus. <IMAGE>
Optical device for measuring cerebral function