Andrea Ying¹, Joan Danielle K. Ongchoco¹; ¹The University of British Columbia

Visual processing of incoming sensory cues gives rise to the rich colours that fill contours and the contours that form objects. But people can also experience colours and contours in the *absence* of explicit sensory cues, albeit in more fleeting ways — as in the phenomenon of “scaffolded attention”. Consider a regular grid of squares. By definition, there is no structure there, but many people report seeing various shapes and patterns anyway (e.g., horizontal lines, block letters). But beyond *what* people see, perhaps more intriguing is *how* they experience it. Some describe the squares of perceived patterns to be brighter or differently shaded (i.e., “shaders”), while others note the squares as being ‘outlined’ or ‘traced’ (i.e., “bolders”). What determines when people experience one ‘type’ over another? Here observers reported which type they experienced, and reproduced the magnitude of bolding and/or shading through an interactive grid. We then explored the influence of *external* grid features (e.g., white squares with black outlines vs. black squares with white outlines), and *internal* factors (e.g., attentional breadth [via the ‘Functional Field of View task; FFOV], and sensitivity to figure-ground boundaries [via the Leuven Embedded Figures Test; LEFT]). First, the proportions of shaders and bolders overwhelmingly differed across grids, with reliably more bolders for black (93.2%) than for white grids (41.1%) — perhaps because the contrast differences change whether the squares or the lines are seen as figure or ground. Second, only the LEFT (and not FFOV) scores predicted whether people would be a ‘shader’ or ‘bolder,’ highlighting the role of segmentation processes in scaffolded attention. Thus, people’s everyday hallucinations can depend on what the mind selects — the squares on the white grids or the lines of black grids — which may be grouped together through different visual routines.