These file attachments have been under embargo and were made available to the public after the embargo was lifted on 4 June 2012.
In order to guide our actions, the human brain relies most on the information that is received from the visual sense. However, the visual input the brain receives through the eyes is often subject to noise and ambiguity. Consider for example a person driving a car throughthe fog. In this situation, the visual information that the brain receives is severely degraded. It is obvious that the brain needs a way to resolve such ambiguities in order to be able to provide the reliable visual information necessary to guide our actions. The neuralmechanisms that are involved in resolving ambiguity in the visual input have been the subject of many studies for over a century. In recent years, many studies have used psychophysics and neuroimaging toinvestigate how and where the brain processes and resolves ambiguous visual information. In this study we used a structure-from-motionstimulus to investigate the neural responses during the viewing of an ambiguous stimulus. To investigate these neural responses underlying ambiguous visual perception we used a novel approach. Intracranial electroencephalography is a relatively new method that provides several advantages over more commonly used methods such as scalp EEGor magnetic resonance imaging. The electrodes that are used to record the electrical activity of the brain are implanted directly on thesurface of the brain. This allows for more accurate measurements ofbrain activity becausethere is no interference from the skull and skin which cause problems in scalp EEG.Using intracranial EEG, we identified two separate locations in the left hemisphere of one partici-pant that showed a significant difference in alpha band power during a switch in perception when viewing an unambiguous stimulus compared to viewing an ambiguous stimulus. This difference could indicatethat the neuronal populations at theselocations respond preferentially to bottom-up visual information and not to top-down visual information. A subsequent analysis of the time-frequency spectrum revealedno significant differences but clearly showed a decrease in power in the lower frequencies before the participant responded to a changein the stimulus. This decrease in power is likely related to the preparation of the motor response. The results of this study show thatintracranial EEG is useful new method that can provide an improvement over both scalp EEG and MRI.