Idiosyncratic characteristics of saccadic eye movements when viewing different visual environments

Eye position was recorded in different viewing conditions to assess whether the temporal and spatial characteristics of saccadic eye movements in diff erent individuals are idiosyncratic. Our aim was to determine the degree to which oculomotor control is based on endogenous factors. A total of 15 nai ve subjects viewed five visual environments: (1) The absence of visual stim ulation (i.e. a dark room); (2) a repetitive visual environment (i.e. simpl e textured patterns); (3) a complex natural scene; (4) a visual search task ; and (5) reading text. Although differences in visual environment had sign ificant effects on eye movements, idiosyncrasies were also apparent. For ex ample, the mean fixation duration and size of an individual's saccadic eye movements when passively viewing a complex natural scene covaried significa ntly with those same parameters in the absence of visual stimulation and in a repetitive visual environment. In contrast, an individual's spatio-tempo ral characteristics of eye movements during active tasks such as reading te xt or visual search covaried together, but did not correlate with the patte rn of eye movements detected when viewing a natural scene, simple patterns or in the dark. These idiosyncratic patterns of eye movements in normal vie wing reveal an endogenous influence on oculomotor control. The independent covariance of eye movements during different visual tasks shows that saccad ic eye movements during active tasks like reading or visual search differ f rom those engaged during the passive inspection of visual scenes. (C) 1999 Elsevier Science Ltd. All rights reserved.