The Flashed Face Distortion Effect Does Not Depend on Face-Specific Mechanisms

Abstract

When normal faces are rapidly presented in the visual periphery, they are perceived as grotesque and distorted. This phenomenon, "The flashed-face distortion effect" (FFDE) is a powerful illusion that may reveal important properties of how faces are coded in peripheral vision. Despite the strength of the illusion (and its popularity), there has been almost no follow-up work to examine what governs the strength of the illusion or to develop a clear account of its phenomenology. Presently, our goal was to address this by manipulating aspects of facial appearance and spatial/temporal properties of the flashed-face stimulus to determine what factors modulate the illusion's strength. In three experiments, we investigated the extent to which local contrast (operationalized by the presence or absence of makeup), image eccentricity, image size, face inversion, and presentation rate of images within the sequence each contributed to the strength of the FFDE. We found that some of these factors (eccentricity and presentation rate) mattered a great deal, while others (makeup, face inversion and image size) made little contribution to the strength of the FFDE. We discuss the implications of these results for a mechanistic account of the FFDE, and suggest several avenues for future research based on this compelling visual illusion.

Figure 1

A schematic view of our basic FFDE paradigm. We presented images in rapid succession on either side of a central fixation point, which observers were asked to maintain fixation on during each trial. On each trial, participants were asked to rate the strength of the FFDE on a 1–7 scale after the image sequence concluded. The set of images to be included in the FFDE sequence was randomly sampled on each trial and their order within the sequence was also shuffled randomly on each trial. Across experiments, we varied a range of stimulus parameters within this basic framework including image orientation, the presence/absence of make-up, the duration of images within the sequences, and the eccentricity and size of those images.

Figure 2

Average distortion ratings across participants for all conditions in Experiment 1. Error bars indicate a 95% credible interval for each data point. While inversion had a weak impact on perceived distortion (see model comparison results in Table 1), makeup had little effect on the strength of the FFDE.

Figure 3

Average perceived distortion across participants for each condition in Experiment 2. Error bars represent 95% credible intervals for each data point.

Figure 4

A schematic view of how we manipulated image eccentricity in Experiment 3A. Observers rated FFDE sequences presented either in central vision (blue rectangle), at the eccentricity used on Experiments 1 and 2 (red rectangle), or at an intermediate eccentricity (green rectangle). Image size was not manipulated in this experiment.

Figure 5

A schematic view of how we manipulated image eccentricity in Experiment 3B. Observers rated FFDE sequences either at the original size (green rectangle), half-size (blue rectangle) or double-size (red rectangle). The eccentricity of the image was fixed at the same distance as Experiments 1 and 2.

Figure 6

Average perceived distortion within each condition for Experiment 3A. Error bars represent 95% credible intervals for each data point.

Figure 7

Average perceived distortion within each condition for Experiment 3B. Error bars represent 95% credible intervals for each data point.