Iconic faces are not real faces: enhanced emotion detection and altered neural processing as faces become more iconic

Abstract

Iconic representations are ubiquitous; they fill children's cartoons, add humor to newspapers, and bring emotional tone to online communication. Yet, the communicative function they serve remains unaddressed by cognitive psychology. Here, we examined the hypothesis that iconic representations communicate emotional information more efficiently than their realistic counterparts. In Experiment 1, we manipulated low-level features of emotional faces to create five sets of stimuli that ranged from photorealistic to fully iconic. Participants identified emotions on briefly presented faces. Results showed that, at short presentation times, accuracy for identifying emotion on more "cartoonized" images was enhanced. In addition, increasing contrast and decreasing featural complexity benefited accuracy. In Experiment 2, we examined an event-related potential component, the P1, which is sensitive to low-level visual stimulus features. Lower levels of contrast and complexity within schematic stimuli were also associated with lower P1 amplitudes. These findings support the hypothesis that iconic representations differ from realistic images in their ability to communicate specific information, including emotion, quickly and efficiently, and that this effect is driven by changes in low-level visual features in the stimuli.

Keywords: Emotion; Event-related potentials; Expressions; Face perception; Iconic faces; P1.

Fig. 1

An example of the five stimulus sets used and a time course of a single trial for Experiment 1. The “Cartoon” and “Mid-cartoon” stimulus sets have less complex features than the “Rotoscoped” and “Mid-rotoscoped” sets, and the “Cartoon” and “Rotoscoped” stimulus sets are higher in contrast than the “Mid-cartoon” and “Mid-rotoscoped” sets. Photos may have other low-level featural differences in addition to contrast and featural complexity, but are used here as a baseline non-schematic condition

Fig. 2

An example of each type of stimulus set for each type of emotional expression used

Fig. 3

Accuracy rate for five stimulus categories at each presentation time for Experiment 1. Error bars represent standard error of the mean. Dotted lines denote low featural complexity stimuli, with solid lines as high featural complexity stimuli. Circle markers denote high contrast stimuli, with triangles as low contrast stimuli. Photo, the baseline stimulus set, in marked in black. Chance is at 25 %

Fig. 4

Accuracy for all but the photorealistic photo sets in Experiment 1, arranged to illustrate the separate effects of contrast and featural complexity. Error bars represent standard error of the mean

Fig. 5

P1 data at sensor Oz for Experiment 2. The waveforms at the top show the three stimulus sets averaged across all participants. The charts below represent the latencies and amplitude of those individual peaks averaged together. * Significant difference at P < 0.05