Visual Selection in Human Frontal Eye Fields

Frontal eye field neurons discharge in response to behaviourally relevant stimuli that are potential targets for saccades. Distinct perceptual and oculomotor processes have been dissociated in the monkey FEFs, but little is known about the perceptual capacity of human FEFs. To explore this, transcranial magnetic stimulation (TMS) was applied over the FEFs while subjects carried out visual search. TMS impaired search performance (d’) when applied between 40 and 80ms after search array onset. Unit recordings show that FEF signal during this time period predicts monkeys’ behavioural reports on hit, miss, false alarm and correct rejection trials. Our data demonstrate that the human FEFs make a critical early contribution to search performance. We argue that this reflects the operation of a visuospatial selection process within the FEFs that is not reducible to saccade programs.