Visually similar components within an object will be perceived as groups. Similarities can originate from features including shapes, size, colour and shading.
When similarity amongst components occurs and grouping is perceived, an element can be highlighted if it is dissimilar to the others. When this occurs it is known as an anomaly.
In user interface design the Principle of Similarity can be leveraged to increase the learnability of a product, to guide users’ expectations, or, where an anomaly occurs, it can help focus the user on an important element, such as a Call to Action (CTA) button.