Target-Induced Fine-Scale Gaze Distribution Characteristics

Fixation behaviour can vary with both oculomotor control processes and visual target properties. Previous studies have frequently used high-sampling-rate gaze-position recordings to characterise fixation dynamics, particularly at fine temporal resolution. The present study focuses on gaze-position characteristics at temporal scales below approximately 10 Hz, which overlap with temporal ranges relevant to visual perception and cognitive processing. We define the term fine-scale gaze distribution (FiGa) to describe the distribution of gaze positions during fixation and examine its relationship with visual target properties, particularly target size. We analysed 3997 fixation windows across 13 target sizes ranging from 12 to 128 px. FiGa was quantified using BCEA68, with RMS radial deviation as a complementary measure. Across the full target-size range, absolute dispersion increased with target size: mixed-effects models predicted a 12.5% increase in BCEA68 and a 5.4% increase in RMS from 12 to 128 px. Exploratory piecewise comparisons further suggested a two-hinge-like pattern at intermediate target sizes. For the matched 48/64 px candidate, model-based 95% confidence intervals for both slope changes excluded zero, whereas the corresponding fixed-window hierarchical-bootstrap percentile intervals included zero. Together with the post hoc selection of candidate hinge locations, these results indicate that the local pattern should be interpreted as exploratory, with uncertainty in the precise hinge locations. Overall, FiGa showed two target-size-related characteristics: a broad increase across the full target-size range and an exploratory two-hinge-like pattern at intermediate target sizes.