Can optic flow recalibrate the perceived straight ahead in the visual control of steering toward a goal?

Abstract

There has long been a debate on which of the following two strategies we adopt while we are steering towards a stationary target: (1) The optic flow strategy, which suggests that we can find our ways towards our target by the alignment of our visually perceived heading, our instantaneous direction of locomotion, with the target. (2) The perceived direction strategy, in which we move towards a target by aligning our perceived straight ahead with the target. As we typically walk straight forward in our daily lives instead of making crab movements, our heading is usually well aligned with our perceived straight ahead while we are walking and it is difficult to tell which of the two strategies a person adopts when we observe him or her walking in naturalistic settings.

There are multiple methods to displace the visual information about heading from our perceived straight ahead during walking, but inconsistent results have been obtained with these different methods – some showed that only the perceived direction strategy is used, while some found signs that both strategies are used simultaneously. Researchers supporting the perceived direction strategy suggested that the deviation of participants’ locomotive paths from that predicted by the perceived direction strategy observed in some experiments could be due to participants’ shifts in their perceived straight ahead driven by the displaced heading paradigm. So far, little work that addresses this concern have been conducted, thus, this thesis is intended to investigate this issue. In experiment I, participants were required to steer in virtual environments under displaced optic flow, with their steering performance as well as their shifts in perceived straight ahead at the end of each trial measured. A shift of the perceived straight ahead was observed, and its magnitude increased in conditions with richer optic flow. However, after taking this shift into account, participants still steered on paths intermediate between that predicted by the two different strategies. In experiment II, we have shown that a long period of steering under displaced heading can drive adaptations in our perceived straight ahead and corresponding changes in our steering behavior. From the results we conclude that optic flow has a profound effect on our perception of perceived straight ahead, and on top of that effect, optic flow also directly influences our guidance of steering towards a target.