Mechanisms of Recognition: Change-Blindness and the Perception of Pictures

Mechanisms of Recognition: Change-blindness and the Perception of Pictures

By Ron Gallagher

We see with the brain, not with the eyes.  Paul Bach-y-Rita

[pic 1] 

Figure 1  John Constable, Salisbury Cathedral from the Bishop’s Grounds, 1820. Oil on Canvas, National Gallery of Canada, Ottawa

How does our perception of the brown smudges in Constable’s Ottawa study of Salisbury Cathedral (fig. 1) relate to how we see cows in real life? If Flint Schier is to be believed, looking at that brown smudge is triggering something in us that is triggered by an encounter with the real thing. This seems unfeasible. Even when we look at the Wivenhoe Park cows (fig.2 -Friesians and Herefords, I think) it is still hard to say that this is much like seeing real cows.

[pic 2]

Figure 2  John Constable, Wivenhoe Park, 1816. Oil on canvas. National Gallery of Art, Washington, DC, USA

The working hypothesis of this thesis is that the techniques of artists and photographers mobilize the same mechanisms of recognition which we use to see objects and scenes in the world. Schier has proved a reliable guide so far, and his “two-hypotheses” thesis requires that we entertain the possibility, however remote, that our visual system at some basic level takes these paint marks to be cows. In short, I need to show that seeing a picture of a cow is far more like seeing a cow in real life than you might suppose. I propose to demonstrate this by relating aspects of how we see pictures to aspects of how we see things in the world. Following Michael Podro, I will show how artists “sustain recognition” by mobilizing the mechanisms of visual cognition. My first example shows how pictorial composition mobilizes recognitional abilities.

Composition, Change Blindness and Visual Metacognition

David Wooding’s experiment at the National Gallery’s “Telling Time” exhibition in 2000-2001 tracked the eye movements of over five thousand gallery attendees as they looked at paintings. The results show that in the majority of cases we only look carefully at parts of the picture towards which the artist’s composition directs our eye. One of the paintings in the study was Veronese’s Christ addressing a Kneeling Woman (fig. 3) and we can see that viewers’ eyes have been strongly drawn to the upper torso of the two main figures, to the exclusion of the other parts of the painting.

[pic 3] 

Figure 3  Aggregated fixations from 131 subjects viewing Paolo Veronese’s Christ addressing a Kneeling Woman. Subjects’ gaze is drawn to the two main figures. (Original image © National Gallery, London, annotations © IBS, University of Derby, UK, courtesy of David Wooding.)

Veronese has directed the viewers’ attention through colour and brightness contrast, and by connecting the gazes of the main characters. This compositional technique is augmented by the alignment of heads and the gaze of the other characters who are looking towards Christ and the kneeling woman.

What Wooding’s experiment reveals is that contrary to Gombrich, the symmetry of composition does not work against representation of the subject, but enhances it by capitalising on mechanisms of visual cognition. We are drawn to look at the two main characters because Veronese is manipulating our visual mechanism using gaze, colour light and composition. Podro takes issue with Gombrich treating “convincing representation and the pursuit of pictorial order as reciprocally curtailing” and argues:

these demands may sustain each other: symmetries or correspondences are ways in which we see one form on analogy with another and project one aspect onto another; this is integral to how recognition is sustained and developed.^[1]

Podro examines a similar technique of alignment, gaze and symmetry being used in Ghiberti's panel of the Adoration and Leonardo's Adoration. He further argues that, not only do deliberate techniques of the artist sustain recognition of the subject, but seemingly accidental features of a drawing or paintings, such as unfinished edges, roughly sketched lines and the texture of the paint, are recruited to the depiction of the subject.

[pic 4]        

Figure 4 Leonardo Da Vinci, Head of a girl, c. 1483, Silverpoint and white highlights on prepared paper, 181 x 159 mm, Biblioteca Reale, Turin

If we apply this line of thinking to the Leonardo drawing Head of a Girl, which we discussed in the last chapter (fig. 4), we can imagine that if we used Wooding’s eye-tracking technique to reveal which parts of the picture we were most fixated-on, it would almost certainly be the girl’s eyes. The rest of the picture would hardly get a glance. Thus, one reason Leonardo hasn’t rendered the rest of the picture is because he knows that, given his composition, the viewer simply wouldn’t attend to the hair and the shoulders even if he had drawn them.

This explanation seems at odds with Schier’s speculation that it is “frame knowledge” that enables us to discount these accidents of technique. In fact, the two explanations are compatible – both claim that our visual system effectively ignores or throws away a good deal of the visual information that presents to our field of view. This is confirmed by the research on change blindness and inattention blindness that has been conducted over the last few years. All the evidence from these studies indicates that we notice and remember very little from a visual scene. Furthermore, we vastly overestimate our own and other people’s abilities to attend to and recall what we see. Rather curiously, this phenomenon was predicted by Daniel Dennett in 1991.^[2] In a review of change blindness research, Laura Spinney summarises its impact on vision research:

Until the last decade, vision researchers thought that seeing really meant making pictures in the brain. By building detailed internal representations of the world, and comparing them over time, we would be able to pick out anything that changed. Then in 1991, in his book Consciousness Explained, the philosopher Daniel Dennett made the then controversial claim that our brains hold only a few salient details about the world--and that this is the reason we are able to function at all.

We don't store elaborate pictures in short-term memory, Dennett said, because it isn't necessary and would take up valuable computing power. Rather, we log what has changed and assume the rest has stayed the same. Of course, this is bound to mean that we miss a few details. Experimenters had already shown that we may ignore items in the visual field if they appear not to be significant--a repeated word or line on a page of text, for instance. But nobody, not even Dennett, realised quite how little we really do "see".