Functional Near Infrared Spectroscopy (fNIR) is a measure that reflects the dynamics of cerebral blood flow. Task performance activates certain brain areas which leads to enhanced oxygen consumption by cells in those areas and therefore enhanced blood flow to those cells. fNIR a lower-cost non-invasive alternative to fMRI that is gaining popularity among neuroscientists. Unlike fMRI, this optical neurotechnology penetrates only a few millimeters below the skull and thus, does not reveal the activity of deeper brain structures. Nevertheless, the higher cognitive functions relevant to the study of learning and instruction such as visuo-spatial processing or executive control are localized within the superficial layer of brain tissue called the cerebral cortex, which is readily accessible to fNIR.

As most neuroimaging methods, fNIR has its functional and practical limitations. Unlike PET or fMRI, fNIR cannot measure deep brain structures and it is generally limited to measuring cerebral blood flow dynamics in the forehead, as hair can introduce noise into the optical signal. Another weakness of fNIR is its low temporal resolution, as it takes several seconds for a fNIR sensor to detect changes in blood in the brain. Finally, since most current research in fNIR concerns validating the tool itself, extensive applications in cognitive neuroscience conducted with brain imaging techniques such as EEG have yet to be implemented with fNIR.