INFORMATIONAL CHARACTERISTICS OF THE DOUBLE-STEP SACCADIC EYE MOVEMENTS

Abstract

Saccades have traditionally been studied in response to suddenly changing visual stimuli, such as jumping targets. The evaluation of saccadic eye movements based on the analysis of eye jump trajectories as reaction to the jumping targets is complicated. Time delays and errors of eye jumps are related to the target amplitudes and sequence presentation and must be determined in each type of the experiment. In this research, information theory concepts are used to evaluate the control system of the saccadic eye movements which is defined as the information transfer channel. In this case, target jumping on the screen is defined as the input or the source information, the eyesight response trajectory on the screen – as the output information and the difference between them – as the lost information. The amount of information transferred over oculomotor channel is defined as the difference between the input and the lost information rates. Majority of the saccadic eye movements are executed by two-step jumps: primary and corrective saccades. Therefore, the amount of information transferred over oculomotor channel has been measured separately after primary saccades and corrective saccades. We have found that the amount of information obtained during corrective saccades is two times larger than during primary saccades. Primary saccades with bigger amplitudes give more information despite a larger scatter of position errors at the end of jump for them. Theoretical and experimental investigation let us formulate that channel information capacity of the saccadic oculomotor system is in the range of 14 - 15 bits/sec. This value was obtained when the intersaccadic interval was in the range of 0.4 – 0.5 sec.