Bistability and hysteresis in the proximity-based grouping of dot lattices

Grouping by proximity is a fundamental principle of human vision where elements close to each other are perceived as a group. This study examined the hysteresis effect in proximity-based grouping of dots in rectangular lattices in the presence of orientation biases. To induce perceptual switching, interdot distances in a specific direction were gradually increased or decreased on a trial-by-trial basis during ascending and descending sequences. To address orientation biases, stimuli were presented along two axes, each with two orientations. This design allowed investigation of perceptual switching between vertical and horizontal grouping in the cardinal axis and between 45° and 135° grouping in the oblique axis. Data from 34 participants were analyzed by fitting psychometric functions and the Lotka-Volterra-Haken (LVH) model-a dynamical model of neural population competition-with statistical analysis using linear mixed-effects models. The results revealed a strong preference for the vertical orientation in the cardinal axis and a slight bias toward 135° in the oblique axis. A significant hysteresis effect was found in both axes, with ascending transition points consistently exceeded descending points. Interestingly, this effect remained unaffected by stimulus axis or orientation, indicating robustness against orientation biases. A significant positive correlation in hysteresis across axes suggests it may represent a personal perceptual characteristic. The LVH model's numerical simulation effectively captured the dynamic behavior of competing responses and their bifurcation during perceptual switching. The model demonstrated acceptable accuracy in estimating transition points and simulating individual responses. Moreover, its parameters reflected the observed data patterns and provided a mechanistic account of perceptual switching in proximity-based grouping.