Perceptual grouping by proximity principle in dot lattices adheres to Weber’s law in the presence of orientation biases.

The human visual system naturally organizes complex visual scenes by grouping elements based on their spatial proximity, a phenomenon known as the perceptual grouping by proximity principle. This study examined whether the proximity principle adheres to Weber's law and how orientation biases modulate this relationship. Rectangular dot lattices were used to generate the stimulus set at four different scales. The method of limits was used to extract psychophysical difference thresholds for proximity grouping and to derive Weber curves, including the point of subjective equality, just noticeable difference (JND), and Weber fraction. To achieve this, the perceptual shift between different grouping percepts was induced by gradually varying interdot distances along one direction in ascending and descending sequences, whereas distances in the other direction were held constant. Twenty-four right-handed individuals (13 women, 11 men) participated in the experiment. Linear mixed-effects models were used to analyze the collected data. The results revealed a strong preference for vertical orientation and a slight tendency toward a 135° orientation. More importantly, a linear increase in the JND and a constant Weber fraction were observed across lattice scales. These findings indicate that the proximity principle adheres to Weber's law in both axis orientations. However, the vertical bias resulted in decreased sensitivity and resolution in detecting stimulus changes along the orthogonal axis, as evidenced by a higher JND slope and Weber fraction. (PsycInfo Database Record (c) 2026 APA, all rights reserved).