The spatial imprecision in Claude Monet’s Rue Montorgueil in Paris, Festival of June 30, 1878 is more than simple blurring — Monet’s approach reflects the way our peripheral vision works. The spatial imprecision generates a vitality because it is consistent with a single glance at a moment in time.

The flags along Rue Montorgueil look fine when you first glance at the painting, but not if you look directly at them, or after you study the details carefully. This effect is called illusory conjunction. The painting’s spatial imprecision is not so noticeable at first because our own spatial imprecision allows illusory conjunctions to complete the objects. This explains why we see complete flags in the painting (above right), even though many of them are just a single stroke of paint.

In Monet’s festival, the low spatial resolution lends vitality to the painting, as if we are glancing all around the scene. In the above portraits by Pierre-Auguste Renoir (1841-1919) and Edgar Degas (1834-1917), the low spatial resolution has an opposite effect: it focuses our attention. Notice how the faces and eyes of the women are detailed and have high contrast. At the same time, the extremities and the background are noticeably blurrier. This method of blurring was not a new invention. It had been used in portraiture since the 18th and the early 19th centuries by artists such as Gilbert Stuart (1755-1828). Although Stuart’s backgrounds are usually described in more conventional terms, such as “atmospheric” or “freely brushed in,” they have the same effect.

The detailed faces of the portraits encourage our gaze to repeatedly return to the women’s eyes. In doing so, the painting mimics the resolution of our visual system and our way of directing our gaze at the subjects’ eyes.