Research reportInternally versus externally mediated triggers in the acquisition of visual targets in the horizontal plane

- We studied eye-head coordination during visual target acquisition.
- The motor pattern of target acquisition depends on the way of triggering the command.
- There is difference in performance between a verbally given and a memorized command.
- The difference concerns latency, head velocity, acceleration and amplitude.
- The results from this investigation have operational importance.

In an operational setting acquisition of visual targets using both head and eye movements can be driven by memorized sequence of commands - internal triggering (IT) or by commands issued through secondary operator - external triggering (ET). The primary objective of our research was to examine differences in target acquisition using IT compared with ET. Using a forced time optimal strategy eight subjects were required to acquire targets with angular offsets of ±20°, 30° and 60° along the horizontal plane in both IT and ET conditions. The data showed that the eye/head latency difference in IT condition is longer than that for ET, the target acquisition time is also longer for IT commands. Consistent with this finding were similar results when examining the peak head velocity and peak head acceleration. Under IT protocol head amplitude is higher than when using ET.In conclusion, the study demonstrates that the pattern of performance of target acquisition task is influenced by the way of command triggering.