The bookend effect.

Area of Science:

• Visual perception
• Gestalt principles
• Motion perception

Background:

• The principle of common fate suggests objects moving together are perceived as a group.
• Illusory motion can arise from static visual stimuli, such as oblique gratings causing the furrow illusion.

Purpose of the Study:

• To investigate how conflicting illusory motion paths affect the perception of group motion.
• To determine the influence of salient elements on perceived group direction when visual cues diverge.

Main Methods:

• Presenting horizontally aligned targets moving vertically over static background gratings with varying orientations.
• Manipulating background orientation between outer ('bookend') and inner ('book') targets to create conflicting illusory paths.

Main Results:

• When all background gratings shared the same orientation, group motion aligned with the furrow illusion.
• When outer targets had different background orientations than inner targets, perceived group motion was dominated by the outer targets.
• Inner targets' discriminable features and relative motion were insufficient to alter perceived group direction.

Conclusions:

• Spatial proximity and common motion create a unified object representation, prioritizing salient features.
• Dominant visual cues, like the motion of salient 'bookend' elements, override conflicting illusory motion information from inner elements.
• Perception of group motion is susceptible to the influence of visually dominant components, even when other cues suggest different motion paths.