Manual estimations of functionally graspable target objects adhere to Weber's law

Area of Science:

• * Cognitive Psychology
• * Human Perception
• * Motor Control

Background:

• * Manual estimation tasks assess how humans perceive object size by adjusting finger spread.
• * Previous research indicated adherence to Weber's law, suggesting visual information mediation.
• * Recent studies suggested violations of Weber's law for large objects due to biomechanical constraints.

Purpose of the Study:

• * To investigate whether manual estimations adhere to Weber's law across a range of functionally graspable object sizes.
• * To determine if biomechanical limitations, rather than visual perception, influence manual size estimations.
• * To re-evaluate the role of visual information in manual size perception.

Main Methods:

• * Participants performed a manual estimation task, adjusting thumb-forefinger distance to match target object sizes.
• * Target object sizes were scaled to individual participants' maximal aperture separation (10-80%).
• * Just-noticeable-difference (JND) scores were calculated at each size increment.

Main Results:

• * Just-noticeable-difference (JND) scores increased linearly with increasing target object size.
• * These results demonstrate adherence to Weber's law across the tested range.
• * No evidence of biomechanical limitations violating Weber's law was found within functionally graspable sizes.

Conclusions:

• * Manual estimations of 'graspable' target objects adhere to Weber's law.
• * These estimations are primarily mediated by relative and perception-based visual information.
• * Biomechanical constraints do not appear to limit manual size perception within functional aperture ranges.