Revealing temporal dynamics of the visuomotor system via continuous tracking of position and attribute.

Continuous tracking is the recently developed psychophysical technique for efficiently estimating human visual temporal characteristics. The standard version of the task, referred to as position tracking (PT), asks participants to track the location of a continuously moving target by a motor response (e.g., mouse movement). Some studies have also used a variant method, attribute tracking (AT), which requires participants to track and reproduce a continuously changing attribute (e.g., luminance) of the target instead of position. For both PT and AT, the temporal dynamics of the entire system from vision to action can be estimated from the cross-correlogram (CCG) of the trajectory between the stimulus and response. The similarities and differences in CCG between PT and AT, however, remain elusive but were examined in this study. Experiment 1 compared the two CCGs using luminance-defined circular patches, color-contrast-defined patches, and luminance-defined patches with various spatial frequencies. The results indicate that the PT response was faster and less affected by the stimulus variables than the AT response. Experiment 2 showed that these differences could be reduced by making the visuomotor mapping of PT less direct by reversing the motor response direction and by making the local stimulus change magnitude comparable between PT and AT. The comparison with the traditional reaction time measures (Experiment 3) further showed that the peak latency of CCG from PT aligned better with the simple reaction time, whereas that from AT aligned better with the choice reaction time. These results indicate that CCG is more sluggish for AT than for PT because AT includes the process of identifying the stimulus content (attribute change direction) and mapping it to a motor response arbitrarily specified by the experimenter, and because the effective stimulus change magnitude for AT is often weaker than that for PT. These findings provide a clearer understanding of the meaning of CCGs measured by the two types of continuous tracking tasks.