Abstract
During locomotion in natural terrains, humans look closer to the body in more complex terrain presumably due to the need for more precise visual information about the 3D structure of the terrain in order to guide footholds (Bonnen et al., 2021). They also slow down as the terrain becomes more complex and gaze is found to fall on a location approximately 1.6 sec ahead, over a range of walking speeds from 1.4 to 0.9 m/s (Matthis et al., 2018). A similar look-ahead time has been observed in driving (Land & Lee, 1994) and other contexts. It is possible that this reflects the time constant of working memory decay that modulates the precision of the information needed to plan future steps. To explore the generality of this finding, we collected gaze data using a Pupil Labs Invisible eye tracker while subjects rode a bicycle around campus. As with walking, subjects alternated between stable gaze locations (fixations) on the ground plane and fixations to more distant locations. The ground plane was reconstructed using photogrammetry. Fixations were identified as periods separated by saccades, where the velocity of the eye-in-orbit was less than 100 deg/sec, as the eye counter-rotates in the orbit during forward motion. Fixations ranged from 1.9 to 9.2 meters ahead, with speeds varying between 0 and 7.9 m/s. Preliminary results suggest that subjects have a constant look-ahead time with a mean of 1.1 +/- 0.02 seconds. This is slightly shorter than the look ahead time while walking or driving, but still consistent with the idea that the quality of the sensory information may be limited by working memory decay. Other factors such as spatial resolution at these distances, and the momentum of the bicycle may also need to be considered.