Thay vì góp phần ổn định hiện trường trực quan, mục tiêu hướng saccades nhấn mạnh các đối tượng đặc biệt có hình ảnh được foveated để nâng cao sự giám sát của họ. Các đối tượng phục vụ là mục tiêu của saccade có thể được chỉ ra từ một số người khác bằng một quá trình lựa chọn liên quan đến việc xem xét cẩn thận các tính năng đối tượng | slow gaze-stabilizing movements can follow 1 . Rather than contributing to stabilizing the visual scene target-directed saccades emphasize particular objects whose images are foveated in order to improve their scrutiny. The object serving as target of a saccade may be singled out from a number of others by a selection process that involves a careful consideration of object features and the expectations and needs of the observer. Such target-directed saccades are Lisri-ally referred to as goal directed 2 Alternatively the target for a saccade may be an object appearing unexpectedly requiring immediate attention and therefore prompting a reflectory orienting saccade. Objects serving as targets of saccades may be defined by visual auditory or tactile cues. Objects whose location defines a desired location for the eyes do not have to be present at the time the saccade is carried out. Rather fairly precise saccades can be elicited based on memorized information on the target location memory-guided saccades . Antisaccades are a specific example of a spatial dissociation of object location and saccade goal resulting from the instruction to invert the vector defining the object location in order to generate a saccade vector 3-5 . Finally spontaneous saccades may be generated in the absence of any guiding sensory cues defining goals in the external world solely determined by endogenous goals. Irrespective of the circumstances causing a saccade all saccades are fast ballistic eye movements reaching maximum velocities up to 500 per second and more and are usually completed within tens of milliseconds. Despite their speed saccade trajectories tend to be remarkably stereotyped both within and across individuals. The duration and peak velocity of saccades increases monotonically with the amplitude of the movement in a consistent way usually referred to as the main sequence 6 fig. 1 . Saccade latency is defined as the delay between the presentation of the cue and the onset of the
