Common Visual Preference for Curved Contours in Humans and Great Apes

Abstract

Among the visual preferences that guide many everyday activities and decisions, from consumer choices to social judgment, preference for curved over sharp-angled contours is commonly thought to have played an adaptive role throughout human evolution, favoring the avoidance of potentially harmful objects. However, because nonhuman primates also exhibit preferences for certain visual qualities, it is conceivable that humans' preference for curved contours is grounded on perceptual and cognitive mechanisms shared with extant nonhuman primate species. Here we aimed to determine whether nonhuman great apes and humans share a visual preference for curved over sharp-angled contours using a 2-alternative forced choice experimental paradigm under comparable conditions. Our results revealed that the human group and the great ape group indeed share a common preference for curved over sharp-angled contours, but that they differ in the manner and magnitude with which this preference is expressed behaviorally. These results suggest that humans' visual preference for curved objects evolved from earlier primate species' visual preferences, and that during this process it became stronger, but also more susceptible to the influence of higher cognitive processes and preference for other visual features.

Fig 1. Example of contour pair.

Same semantic meaning and different contour. From Bar & Neta (2006), used with their permission.

Fig 2. Example of content pair.

Same kind of contour and different semantic meaning. From Bar & Neta (2006), used with their permission.

Fig 3. Trial sequence of Experiment 1.

A fixation cross shown for 500 ms, followed by a pair of stimuli for 80 ms, immediately replaced by a pair of grey squares, and the chosen image was shown once again, centered, and enlarged.

Fig 4. Proportion of curved stimulus choices by humans and great apes.

From left to right, 95% confidence interval of the proportion of curved choices by humans when stimuli pairs were presented for 80 ms (Experiment 1) and until response (Experiment 2), and by great apes when stimuli pairs were presented for 84 ms (Experiment 3) and until response (Experiment 4). The red line at value .50 indicates chance-level choice.

Fig 5. Consistency in the choice in humans and great apes.

From left to right, 95% confidence interval of humans’ choice consistency when stimuli pairs were presented for 80 ms (Experiment 1) and until response (Experiment 2), and by great apes when stimuli pairs were presented for 84 ms (Experiment 3) and until response (Experiment 4). The red line at value .50 indicates chance-level consistency.

Fig 6. Consistency in the choice of curved and sharp-angled contours only in great apes.

Consistency results from Experiments 3 and 4. From left to right, 95% confidence interval of great apes’ choice consistency when stimuli pairs were presented for 84 ms for sharp-angled and curved contours (Experiment 3), and when stimuli pairs were presented until response for sharp-angled and curved contours (Experiment 4). The red line at value .50 indicates chance-level consistency.