| At first glance, aesthetic preference -- how a given image or piece of art looks to you, makes you feel -- would seem to be a purely cultural construct, something you've learned along the way during your life. It has been found that this isn't the whole story, and that some measure of aesthetic appreciation is influenced by how a picture is constructed, and not its actual content. More curious still, this influence is only apparent in right-handed people, suggesting a fundamental difference in aesthetic perception between the left and right-handers.
A 1976 study done by J. Levy had participants (all of whom were right-handed) choose which of two nature scenes they found more aesthetically pleasing. Each scene was presented once normally, and once with the same image mirrored vertically. For 90% of the scenes, scores were the same for both orientations, thus there was no aesthetic difference between the two. However, for the remaining 10%, the right-handers showed a statistically significant preference for one orientation over the other -- there was something intrinsically more pleasing about the image when it faced that way.
She then asked a different set of participants whether the same set of images had their most important content on the left or right side, or if it was equally balanced. When correlated, the data showed that the images judged most aesthetically pleasing had their primary content on the right side of the image, while those judged neutral had either balanced or left-oriented content. Levy further went on to conduct the same test with left-handers, and no difference was found between test scene orientations, so no content correlations could be made. In other words, right-handed people found content more pleasing when it was on the right, while left-handed people didn't show any bias either way. This finding was reinforced by other researchers' studies, which used (among other images) vacation slides and simple drawings.
While the findings are clear, the implications are not. Levy's theory was that analysis of an image based on aesthetic principles required more activation of the right side of the brain, which is responsible for most kinds of visiospatial analysis. The eyes are bilaterally wired to the brain (in a confusing way: each eye's visual field is split down the center between the left and right visual cortices, but wired contralaterally so that the left side of the field stimulates the right VC and vice versa), meaning that both sides would seem to be equally stimulated by most images. In the case of the pleasing test images, though, the right sides were the ones with more complexity, which means the left brain was additionally activated. Hence both hemispheres would be more equally activated and the resulting image would seem more balanced, and thus more pleasing. Since left-handers do visiospatial analysis on both sides of the brain, the bias wouldn't be present for them.
This wasn't easily provable, and other researchers formed different explanations for the effect. J. G. Beaumont (1985) suggested that the content on the right forced both eyes to focus there, so the majority of the entire image was in the left visual field. Since the left visual field feeds the right brain, and the right brain does visiospatial analysis, a greater percentage of the image would be processed by it, and theoretically it would thus be more pleasing. Another theory, by M. T. Banich (1993), explained that the density of information on the right was fed to the left brain, which was better at processing and interpreting detail. The right brain, better at putting together information, received the less complex information and formed global context for the details to make sense in.
It's known (or at least mostly accepted) that mood is dependent on greater or lesser activity in either side of the brain, specifically in the frontal regions. Greater activation on the right frontal area pushes people towards depression and negativity, while greater activation on the left side puts people in a cheerful, positive mood. This is why the left hemisphere is targeted by procedures like ECT and TMS. This provides for the possibility that having detail in the right visual field stimulates the left brain, improving mood and causing pleasure. While I can't find any citation for this theory, it's supported by work by W. Heller (1988) and R. J. Davidson (1984) that shows people will judge identical images more negatively when presented in the left visual field than the right.
Though this effect holds for advertisements and vacation slides, it's not present for paintings by famous artists, or other recognized art. The first three theories explain the effect in terms of subconscious visiospatial processing, which shouldn't change at all dependent on the stimulus. An emotional explanation, however, makes sense in the context of fine art, which isn't always intended to cause a positive emotional response. Thus, art with greater detail on the left could still have aesthetic value, so long as its intent isn't to portray pure shiny happiness.
Interestingly, the more you look for right-handed bias in images intended to be aesthetically pleasing, the more you will find them. Advertisements spring immediately to mind, where the most salient images and text are often right-aligned on the page. Balanced, good looking websites -- Slashdot and our very own Everything2, for instance -- also tend to have the busiest part of the page located on the right.
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