A tendency to favor objects with contours over objects with sharp angles or points.
When presented with objects that possess sharp angles or pointed features, a region of the human brain involved in fear processing, the amygdala, is activated. Likely a subconscious mechanism that evolved to detect potential threats, this fear response suggests that angular features influence the way in which objects are affectively and aesthetically perceived. Indeed, in experiments where subjects were presented with otherwise similar angled versus contoured objects (e.g., round-faced watches versus square-faced watches), subjects strongly preferred the more rounded, contoured objects. In some of these experiments, brain activity was observed using functional magnetic resonance imaging (fMRI) as subjects indicated their preference. The degree of amygdala activation was proportional to the degree of angularity or sharpness of the object presented, and inversely related to object preference. These effects were observed in both male and female subjects, and suggest an innately rooted contour bias in humans. id="footnote51a"> class="nounder totri-footnote" href="https://www.safaribooksonline.com/library/view/universal-principles-of/9781592535873/xhtml/ch25_fn.html#footnote51">1
The picture is more complex, however, than to simply infer that all designs should be made round to increase their appeal. Objects used in the experiments were emotionally neutral. For example, a baby doll was not used for a contour object as it carries with it a set of positive emotional associations and biases, and a knife was not used for an angular object as it carries with it a set of negative emotional associations and biases. It is clear that absent these competing biases and associations, the contour bias is a relevant influencer of overall perception. The degree to which the bias influences perception when competing biases (e.g., baby-face bias) or semantically relevant perceptions (e.g., criminals use knives) are at play is not yet clear. Additionally, objects with pointed features elicited stronger activations in regions of the brain related to associative processing, meaning that although the angular objects were less liked, they elicited a deeper level of processing than did the contoured objects — they were, in effect, more interesting and thought-provoking to look at. This seems consistent with the kind of innate response one would expect from potential threats and suggests a tradeoff between angular and contoured features: Angular objects are more effective at attracting attention and engaging thought; contoured objects are more effective at making a positive emotional and aesthetic impression.
Consider the contour bias in all aspects of design, but especially with regard to objects and environments that are emotionally neutral. Use angular and pointy features to attract attention and provoke thought. Use contoured features to make a positive first impression. Generally, the degree of angularity corresponds with the strength of amygdala activation, so ensure that the angularity of design elements aligns with the design objectives.