The posterior temporal region of the non-human primate brain (areas MT/MST), and its human homologue, known as area V5 
or human MT complex (hMT+
are responsive to visual motion 
. Electrical stimulation of this region in non-human primates can influence motion direction discriminations, suggesting that its activity is critically linked to perceptual decisions 
. Although fundamental to our current understanding of motion perception, studies in non-human primates cannot ascertain conscious perceptual experiences during these direct alterations of neural activity.
To determine whether a brain region is causally linked to a perceptual experience, one must modulate its neural activity. Causal necessity can be established by inactivation (e.g. lesion) of the brain region and observing a perceptual deficit, whereas causal sufficiency is established by modulating its activity (e.g. by electrical stimulation) and observing a corresponding change in the perceptual experience. Non-invasive methods such as functional magnetic resonance imaging (fMRI) have provided evidence in the human brain of relationships between hMT+
responses and subjective visual motion perception (for review, see 
). However, correlational techniques like fMRI and electroencephalography (EEG) cannot establish a causal relationship between hMT+
activity and conscious motion perception.
Non-human primate lesion studies first demonstrated the necessary role of MT in motion discrimination judgments 
. Subsequent reports addressed the necessity of human MT+
in the conscious experience of visual motion. For instance, visual motion blindness (akinetopsia) was reported in a few patients with extensive stroke in the posterior temporal region 
. Deficits in motion processing have since been reported in healthy controls during transcranial magnetic stimulation (TMS) of posterior temporal cortex 
, in one patient with epilepsy during electrical stimulation of the anatomical area around hMT+
, including superior, middle and inferior temporal and angular gyrus 
, and in a few patients with variable amounts of brain damage in the vicinity of the anatomical locus of hMT+ 
In contrast to these findings of disruption of motion perception, reports of positive percepts caused by functional alteration of hMT+
are missing 
. Although some studies in humans have elicited “motion percepts” by electrical stimulation in various regions of the brain, the precise anatomical location of these stimulation sites and their spatial relationships to hMT+
remain uncertain. Penfield first reported illusory motion caused by electrical brain stimulation (EBS) of the posterior temporal region in some cases of intraoperative monitoring 
. Plant and colleagues 
reported a patient who saw a moving colorless “fog”, without moving objects, during seizure auras as well as during electrical stimulation of epileptic tissue. Lee and colleagues 
reviewed the evidence of visual illusions caused by electrical stimulation of human visual cortex and suggested that the experience of “visual movement” can be elicited at many sites across cortex. We note, however, that the definition of visual movement was not specified. In a study of one patient implanted with intracranial electrodes, Matsumoto and colleagues 
were the first to relate evoked potentials from magnetoencephalography (MEG) during a visual motion task with a patient’s reported illusions of objects moving in depth during electrical stimulation of the posterior superior temporal sulcus.
These previous findings of positive percepts must be interpreted with caution due to several caveats. The cortical tissue causing illusory percepts could have been diseased (epileptogenic), and the presence or absence of epileptic after-discharges (triggered by EBS) was not reported. In addition, the precise location of the stimulation was not adequately established by neuroimaging methods. Indeed, a more recent study failed to produce a visual motion percept by electrical stimulation at the border of fMRI-defined hMT+
in one patient 
, leaving open the question of whether electrical stimulation of hMT+
is sufficient to induce visual perceptions.
The question of the spatial relationship between effective sites of induction of visual illusions by EBS and the site of visual stimulus-induced activity recorded by fMRI and electrocorticography (ECoG) remains unexplored. Moreover, the relationship between fMRI and ECoG signals during motion perception has not been characterized but has the potential to provide a bridge between human fMRI measures and electrophysiological recordings in animals 
. Combining three methods of neuroscientific inquiry (i.e. fMRI, ECoG, and EBS) in the same conscious human subjects allowed us to address the critical link between fMRI and electrophysiological correlates of motion perception and the role of hMT+
in the conscious perception of motion.