Zijiang He¹, Lizhu Yan¹, Lingling Bai¹, Teng Leng Ooi²; ¹University of Louisville, ²The Ohio State University

The intrinsic bias is the visual system’s internal model of the ground surface (Ooi et al, 2001 Nature). It is anchored at the feet’s location of a static observer tested in the dark. However, it is unknown if the anchored location shifts away from the static observer under more natural circumstances such as in the view of a walkable ground surface, and if the relocation/shift requires attentional effort. This is a significant issue as the intrinsic bias, and where it is anchored, is the basis for creating the ground surface reference frame for spatial coding of object locations. Eight observers were tasked to judge the target (0.16 cd/m2, 0.2 degree, 2 seconds) location (4.5, 5.75, 7 m @ 0.14 m height) in the dark using the blind walking-gesturing paradigm. Ten seconds prior to judging, they were exposed for 10 seconds to one of six conditions: 2 viewing environments (dark vs. impoverished) x 3 cognitive demands (neutral, count-number-backward, and lateral gaze-shift). The dark and impoverished environments had the observers exposed, respectively, to total darkness and an array of 2x8 parallel texture elements (0.04 cd/m2) on the floor (spanning 2.25-9.25 m). During the exposure, the observer either remained neutral, counted numbers backward, or directed their gaze alternately to the left and right shoulders (~0.25 Hz). Judged distances were longer in the impoverished-with-neutral condition than the dark-with-neutral condition (p<0.001). This suggests the visual system relocated the intrinsic bias in front of the observer when there was visual texture to define the ground surface. Additionally, data from the impoverished and dark environments became similar (p>0.05) when observers performed number-counting or gaze-shifting, suggesting that attention was required to relocate the intrinsic bias. In the dark environment, judged distances were similar under the three cognitive demands indicating the intrinsic bias remained anchored at the feet’s location.

Acknowledgements: NIH R01EY033190