Impaired saccadic adaptation in schizophrenic patients with high neurological soft sign scores.

Many motor and cognitive alterations in schizophrenia suggest the involvement of the cerebellum. Neurological soft signs (NSS) are frequent in patients with schizophrenia and reductions in cerebellar volume have been associated with high NSS scores. In this study, we tested saccadic adaptation, a well-characterised oculomotor paradigm involving the cerebellum, in schizophrenic patients with high NSS scores.

Saccadic adaptation depends on object selection: evidence from between- and within-object saccadic eye movements.

The accuracy of saccadic eye movements is maintained by saccadic adaptation. Post-saccadic visual feedback about the error between the target position and the saccade endpoint is crucial to the adaptive process. The present experiments examine the adaptation of saccades that select a new target object (between-object saccades) and that of saccades that would not aim for a selected target but execute a fixed motor vector (within-object saccades).

The use of recurrent signals about adaptation for subsequent saccade programming depends on object structure.

Executing sequences of accurate saccadic eye movements supposes the use of signals carrying information about the first saccade for updating the predetermined motor plan of the subsequent saccades. The present study examines the signals used in planning a second saccade when subjects made two successive saccades towards one long or two short peripheral objects displayed before the first saccade execution. Different first eye movement signals could be used: desired eye movement signals, representing the movement necessary for attaining the intended target, or actual eye movement signals, representing the movement actually executed.

Spatial object representation and its use in planning eye movements.

The eye movements we make to look at objects require that the spatial information contained in the object's image on the retina be used to generate a motor command. This process is known as sensorimotor transformation and has been generally addressed using simple point targets. Here, we investigate the sensorimotor transformation involved in planning double saccade sequences directed at one or two objects.

The ability of the saccadic system to change motor plans in scanning letter strings.

Evidence from recent studies bolsters the idea of preestablished motor plans in scanning isolated items. Thus, refixation saccades are preplanned at the same time as the primary saccade directed to a peripheral item and are completed with fixed amplitudes irrespective of the first fixation position in the item. In order to examine the saccadic system's ability to correct the motor plan during its execution on the basis of new visual information, an experiment was conducted in which 11-letter strings were changed to two 5-letter strings at different times after the primary saccade was directed to the stimulus.

Attentional selection during preparation of eye movements.

Two experiments were conducted to examine the relationship between visual attention and saccade programming. Participants had to saccade to a letter string and detect a letter change presented briefly before the saccade onset. Hit probability (i.