Because the human visual system is continually being bombarded with inputs, it is necessary to have effective mechanisms for filtering out irrelevant information. This is partly achieved by the allocation of attention, allowing the visual system to process relevant input while blocking out irrelevant input. What is the physiological substrate of attentional allocation? It has been proposed that alpha activity reflects functional inhibition. Here we asked if inhibition by alpha oscillations has behavioral consequences for suppressing the perception of unattended input. To this end, we investigated the influence of alpha activity on motion processing in two attentional conditions using magneto-encephalography. The visual stimuli used consisted of two random-dot kinematograms presented simultaneously to the left and right visual hemifields. Subjects were cued to covertly attend the left or right kinematogram. After 1.5 sec, a second cue tested whether subjects could report the direction of coherent motion in the attended (80%) or unattended hemifield (20%). Occipital alpha power was higher contralateral to the unattended side than to the attended side, thus suggesting inhibition of the unattended hemifield. Our key finding is that this alpha lateralization in the 20% invalidly cued trials did correlate with the perception of motion direction: Subjects with pronounced alpha lateralization were worse at detecting motion direction in the unattended hemifield. In contrast, lateralization did not correlate with visual discrimination in the attended visual hemifield. Our findings emphasize the suppressive nature of alpha oscillations and suggest that processing of inputs outside the field of attention is weakened by means of increased alpha activity.

The analysis of a peripheral visual location can be improved in two ways: either by orienting one's gaze (usually by making a foveating saccade) or by 'covertly' shifting one's attention to the peripheral location without making an eye movement. The premotor theory of attention holds that saccades and spatial shifts of attention share a common functional module with a distinct neuronal basis. Using single-unit recording from the brains of trained rhesus monkeys, we investigated whether the superior colliculus, the major subcortical center for the control of saccades, is part of this shared network for attention and saccades. Here we show that a distinct type of neuron in the intermediate layer of the superior colliculus, the visuomotor neuron, which is known to be centrally involved in the preparation of saccades, is also active during covert shifts of attention.

The term short-term saccadic adaptation (STSA) captures our ability to unconsciously move the endpoint of a saccade to the final position of a visual target that has jumped to a new location during the saccade. STSA depends on the integrity of the cerebellar vermis. We tested the hypothesis that STSA reflects the working of a cerebellar mechanism needed to avoid 'fatigue', a gradual drop in saccade amplitude during a long series of stereotypic saccades. To this end we compared the kinematics of saccades of 14 patients suffering from different forms of cerebellar disease with those of controls in two tests of STSA and a test of saccadic resilience. Controls showed an increase in saccade amplitude (SA) for outward adaptation, prompted by outward target shifts, due to an increase in saccade duration (SD) in the face of constant peak velocity (PV). The decrease in SA due to inward adaptation was, contrariwise, accompanied by a drop in PV and SD. Whereas patients with intact vermis did not differ from controls, those with vermal pathology lacked outward adaptation: SD remained constant, as did SA and PV. In contrast, vermal patients demonstrated a significant decrease in SA, paralleled by a decrease in PV but mostly unaltered SD in the inward adaptation experiment as well as in the resilience test. These findings support the notion that inward adaptation is at least partially based on uncompensated fatigue. On the other hand, outward adaptation reflects an active mechanism for the compensation of fatigue, residing in the cerebellum.

Psychopathological symptoms in schizophrenia patients suggest that the concept of self might be disturbed in these individuals [1]. Delusions of influence make them feel that someone else is guiding their actions, and certain kinds of their hallucinations seem to be misinterpretations of their own inner voice as an external voice, the common denominator being that self-produced information is perceived as if coming from outside. If this interpretation were correct, we might expect that schizophrenia patients might also attribute the sensory consequences of their own eye movements to the environment rather than to themselves, challenging the percept of a stable world. Indeed, this seems to be the case because we found a clear correlation between the strength of delusions of influence and the ability of schizophrenia patients to cancel out such self-induced retinal information in motion perception. This correlation reflects direct experimental evidence supporting the view that delusions of influence in schizophrenia might be due to a specific deficit in the perceptual compensation of the sensory consequences of one's own actions [1, 2, 3, 4, 5 and 6].