According to surveys of art books and exhibitions, artists prefer poses showing the left side of the face when composing a portrait and the right side when composing a self-portrait. However, it is presently not known whether similar biases can be observed in individuals that lack formal artistic training. We collected self-portraits by naïve photographers who used the iPhone™ front camera, and confirmed a right side bias in this non-artist sample and even when biomechanical constraints would have favored the opposite. This result undermines explanations based on posing conventions due to artistic training or biomechanical factors, and is consistent with the hypothesis that side biases in portraiture and self-portraiture are caused by biologically- determined asymmetries in facial expressiveness.

Introduction

When they compose a self-portrait, artists prefer poses showing the right side of their face [1]–[5]. This right-side bias is well documented by surveys of art books and exhibitions but its origin has remained controversial [6]. As an alternative to observational data from the history of art, we collected self-portraits by naïve photographers who used the iPhone™ front camera in controlled settings. The right side bias remained observable in this non-artist sample, and even when biomechanical constraints would have favored a left-side bias. These results argue against explanations based on posing constraints and support the hypothesis that side biases in portraiture and self-portraiture are caused by biologically determined asymmetries in facial expressiveness [7].

Figure 1a presents a synopsis of the available data on side biases in self-portraiture by artists. We were able to identify five sources of such data. Three were in published papers [1]–[3]. One consisted of unpublished results cited in one of these papers [4]. A fifth source of data came from a recently published monograph on the semiology of self-portraits [5]. Because this last source included a rich selection of works from the Middle Ages up to the twentieth century, we decided to analyze this body of self-portraits for inclusion in our literature review. All the images in the book were included, except those that consisted of “conceptual” or abstract works where no anatomically identifiable face was presented. Because some images were printed twice, all were double-checked to insure that all were counted only once, yielding a total of 214 images. These were classified as showing the left side (88), right side (106), or as frontal (20) by the first author. The classification was straightforward as none of the self-portraits was ambiguous in the posing choice, and very few were frontal.

PPT PowerPoint slide

PowerPoint slide PNG larger image

larger image TIFF original image Download: Figure 1. Artists prefer poses showing the right side of their face when composing a self-portrait. (a) A synopsis of available data on side biases in self-portraits by artists, including, three published studies (1–3), an unpublished study (4), and our own unpublished analysis based on illustrations in a recent monograph (5). Right-handed artists may have found it easier to copy from a mirror placed on the left of the canvas, as in a famous self-portrait by Dutch painter Johannes Gummp (inset). Alternatively, artist may have sought studio arrangements that allowed them to display their left, more expressive side. (b) Percent over-representations of the right (left) side were computed by taking the ratio frequency (right-sided)/total three quarter poses and then subtracting this from 0.5 (expected if there is no bias), within each temporal bin. Thus, negative values signify an over-representation of left-sided portraits, positive values of right-sided ones. https://doi.org/10.1371/journal.pone.0055141.g001

Overall, inspection of Figure 1a confirms a small, but consistent right bias in the side of the face shown on the canvas. A large bias in found in one study that examined only self-portraits by Rembrandt [1], but this is likely to reflect the idiosyncrasies of this specific artist (see also [8]). Further analysis suggested that the bias tends to be strong in the 17th, 18th, and 19th centuries, but weak (and in the opposite direction) before and afterward (see Figure 1b, the huge bias recorded in the 12–14th century window should be interpreted with caution as only seven self- portraits were available in this time window). A temporal dependency of the right-side bias is roughly consistent with an earlier report [2] and strongly suggestive that mirrors may be a part of the explanation for side biases. Mirrors made of polished metal surfaces were available already in the antiquity, and the technique for producing plane mirrors with plated glass surfaces was introduced in Venice around the 14th century. These however were small and expensive, which might have made them less readily available to artists and not suitable for making a full body self-portrait. Techniques for producing larger and cheaper glass plates were gradually introduced only in the 17th century [9]. Assuming that artists have a bias for showing their left- side, this would predict a relative majority of left-sided poses if most drew by memory but a sudden switch to a right-sided preference once most were using mirrors. The invention of photography in mid 19th century [10] obviously implied the brand new possibility of drawing one’s self-portrait from a photograph, although some artists may have continued to use mirrors. These two groups would counterbalance somewhat, cancelling out biases on the average. A recent analysis [11] comparing self-portraits before and after the availability of cameras confirms this interpretation.

However, mirrors could explain the right-side bias in at least two different ways. Artists may be taught to place the mirror on the left of the canvas (as in Figure 1a, inset), a position that should be more natural for a right-handed artist as this avoids occlusion of the reflected image by the arm holding the brush. Such studio conventions and the related biomechanical constraints might well be responsible for a small group bias. As an alternative, the bias may reflect biologically determined asymmetries in facial expressiveness [7]. There is evidence suggesting right-hemispheric dominance for emotional expression [12], which may cause most artists to present their left, more expressive side, to the mirror. When copying the mirror image, these artists would then paint a right-sided face. Distinguishing between these two possibilities would require precise information on artists’ handedness and on the studio arrangements for each analyzed self-portrait, and a large sample. In support of a role for the asymmetry in facial expressiveness, there is evidence for a left- rather than right-side bias when artists compose portraits rather than self-portraits [13]. However, this bias may also arise from biomechanical constraints related to the natural swing of the arm and the direction of the main features of the face as drawn on the canvas [14]. This problem does not apply to a study of photographic portraits in two college yearbooks [15]. Even in this dataset, however, information on how the pictures were taken and later selected for inclusion in the yearbooks would be needed to interpret the results. In addition, a crucial prediction of the facial expressiveness hypothesis is that the bias should be observable even in non-artists. Testing this prediction with paintings is clearly difficult, as non-artists would lack the required technical skills.

We conducted a study of self-portraits by non-artists using the iPhone™ front camera in controlled settings. When using the front camera, the iPhone™ preview display presents a mirror image of the camera view. Thus, our task was representative of what artists do when composing a self-portrait using a mirror, although for our participants this involved a simple button press rather than sophisticated brushwork. The phone then saves the picture in the non-reversed version, that is, as if taken by a photographer facing the participant. Participants explored different poses and recorded their self-portrait once they had found one that they liked. We recorded the participant sex and handedness, and asked whether they had tried making a front- camera self-portrait before. Finally, we showed them the recorded picture and asked to rate it on a 1–7 scale (1 meaning that they did not like it at all, 4 meaning that it was neither good nor bad, and 7 meaning that they liked it very much). This last question was added as an exploratory test of pose preferences in analogy to what would happen if a photographer presented a series of photographs and one had to pick the one that will go into the yearbook. There were three conditions: portrait (phone held vertically, front camera on top, almost centered but slightly offset to the left), landscape left (phone held horizontally, camera on the left of the participant) and landscape right (same as before but camera on the right). This manipulation therefore simulated different mirror positions relative to the artist, allowing us to evaluate the impact of this specific factor.