What can you see? - Some questions about the content of visual experience

29 April 2015 | Dr Tom McClelland (University of Manchester)

Some questions about the content of visual experience.

There are some properties you can see and some you cannot. When you look at the picture below, for instance, what do you see? I see colours such as the yellowness of the banana, I see shapes such as the banana’s curve, I see spatial relations such as the banana’s proximity to the man’s head and I see textures such as the smoothness of the man’s necktie.

There are other properties I don’t see. I don’t see the banana’s property of being a source of potassium or its property of costing 28p. And I don’t see the man’s property of being a member of the Labour Party or his property of being an elder brother. 

On the basis of what I see I might judge that the things I’m looking at have these properties, but that’s not the same as actually seeing those properties. After all, properties like ‘being a source of potassium’ just aren’t the kind of thing that one could see.

The examples I’ve mentioned shouldn’t be too contentious, but there are many kinds of property that do cause controversy. 

For instance, can you see what kind of object something is, such as seeing the smaller object as a banana and the larger object as a man? Can you see causal properties such as the banana being supported by the hand, or affordances such as the banana being edible? Can you see aesthetic properties such as the banana’s beauty, or moral properties such as the man’s virtue? Can you see the identity of objects, like seeing the man as David Miliband?

There is a great deal of debate in philosophy about these contentious cases, and the disputants fall into two camps. 

The first camp are conservatives, and they say that our visual experiences are limited to the basic kinds of property I first listed: colours, shapes, spatial relations and textures (eg Prinz 2012; Brogaard 2010). These conservatives shouldn’t be confused with political Conservatives, but like political Conservatives they are big on austerity – they take an austere view of visual experience that excludes all the contentious properties. 

The second camp are liberals, and this camp adopts a much more inclusive view of perception (eg Siegel 2012; Bayne 2009). They hold that at least some of the contentious properties can be visually experienced. Again, this kind of liberal shouldn’t be confused with political Liberals, but like political Liberals they are endlessly arguing among themselves about just how liberal they should be — the property of being a man is surely permitted as a visible property, but might permitting the property of being virtuous be a step too far?

Now, which camp are you in? The questions I’ve been asking are about what it’s like for you to have the visual experience you have when you look at the photo above. Conservatives would offer an austere description of your experience involving only the limited range of properties that they countenance. If you think that such a description fully captures what your visual experience is like, then you’re a conservative (don’t worry — that doesn’t come with any political commitments). 

If, on the other hand, you think there’s more to your visual experience than is captured by the austere description, then you’re some kind of liberal, and will have to reflect carefully on just how wide the range of properties you can see is.

I’m a liberal, but I’m thinking carefully about just how liberal we should be. Specifically, I’m interested in whether we can see a special category of property called ‘scene categories’. When we open our eyes we don’t just see objects – we also see the wider environments in which those objects are embedded. 

The philosophy of perception tends to focus on our perception of objects — there is endless discussion of whether we can see an object as a pine tree, for instance, but no real discussion of whether we can see a scene as a forest (eg Siegel 2012). I think this is an oversight and that we should ask ourselves whether we can perceive scene categories such as being a forest, being a beach, being a field, being a street, or being a carpark.

Consider the image above. Besides seeing the various shapes, colours, spatial relations and textures in this image do you also see the scene as a forest? Is the scene’s property of being a forest part of your visual experience? 

Conservatives would say that it is not, and would deny that any such scene category can be perceived. They would accept, of course, that we recognise the scene as a forest — they would just deny that this recognition is perceptual. On their view, we see certain patterns of colour and shape and then judge that the scene is a forest. 

However, I think that a combination of empirical and philosophical considerations cast doubt on this conservative view. There are good reasons to adopt a liberal view that acknowledges we can see scenes as forests or as beaches in much the same way as we can see objects as green or as tall. 

Conservatives will need some convincing that we visually experience scene categories, and you might need some convincing too. My case for this has two steps: the first step concerns the ‘visual’ bit of ‘visual experience’ and the second step concerns the ‘experience’.

If conservatives deny that we perceive scene categories, they have to say that we recognise scene categories through some kind of post-perceptual cognitive process, such as making a judgement on the basis of what we see. The empirical data counts against such a view in at least four ways. 

First, judgement is relatively slow, but our recognition of scene categories is incredibly fast. Thorpe et al. (1996), for instance, found that when subjects were shown images in a scene categorisation task, their brains showed Event Related Potentials (ERPs) as early as 150 milliseconds after being shown the image. 

Second, it is generally thought that only attended areas of the visual field are available to judgement, but our recognition of scene categories often seems to be inattentive (see Li et al, 2002). 

Third, the speed at which we make discriminative judgements about a stimulus can generally be improved if we’re familiar with the stimulus, or if we form appropriate expectations about the stimulus. However, an early study by Biederman et al (1983) suggests that familiarity and expectation do not speed up our categorisation of scenes, indicating that scene categorisation is an automatic perceptual process. 

Fourth, perceptual processes display a phenomenon known as ‘perceptual aftereffects’ (which you can find more about here). Post-perceptual processes do not display this effect, but a study by Greene & Oliva (2010) indicates that scene categorisation is susceptible to aftereffects.

Interpreting this data is not always straightforward, but it certainly looks like scene categories can be recognised perceptually, not just through post-perceptual judgements. But I’m not home free yet. 

It’s one thing to perceptually process a property but quite another to perceptually experience it. Since I claim that we perceptually experience scene properties, I have more work to do. This is where some philosophical considerations need to be introduced to supplement the empirical data. 

Liberals use something called ‘contrast cases’ to show that our visual experience is more rich than conservatives think. Contrast cases are pairs of visual experiences that differ from each other in ways that conservatives are unable to account for. Such cases drive the following argument against conservatives:

Here is a classic example used by liberals:

To begin, this image looks to most people like a meaningless jumble of black and white patches. But if you look closely you can recognise it as a picture of a cow (the face is on the left and is looking towards you). 

This revelation changes what your visual experience is like, but the conservative can’t explain this change because there is no difference in the colours, shapes (etc.) that you see. Surely what changes is that you start to see the image as a cow? 

Conservatives deny that we see this kind of property, but this contrast case suggests they are wrong. Perhaps a similar example can be found in which we come to visually experience a scene category. Consider the following image:

Again, you might start by seeing meaningless patches of black and white but then come to recognise that this scene is a waterfall. To make sense of this change, it seems we must say that we visually experience the property of being a waterfall. Here’s another kind of example often used by liberals:

You might first recognise this image as a rabbit then recognise it as a duck. Your visual experience represents the same conservative-permitted properties in both cases, so the change must involve some more contentious property, such as visually experiencing the image first as a rabbit then as a duck. Again, we might be able to find a counter-part to this example involving scene categories. Consider the following image:

These sand dunes look a lot like waves, and you might be able to switch between visually experiencing this scene as a desert then visually experiencing it as a sea. If so, this would again be a case in which we see scene categories.

Although these brief arguments are far from conclusive, they offer a taste of the larger case I hope to make in favour of the visibility of scene categories. Ultimately though, there’s only one way to decide where you stand on these issues, and that is to ask yourself what you can see!

References

Bayne, T. (2009). Perception and the Reach of Phenomenal Content. Philosophical Quarterly, 59(236), 385–404.

Biederman, I., Teitelbaum, R. C., & Mezzanotte, R. (1983). Scene Perception: A Failure to Find a Benefit From Prior Expectancy or Familiarity. Journal of Experimental Psychology, 9(3), 411–429.

Brogaard, B. (2013). Do we perceive natural kind properties? Philosophical Studies, 162 (1), 35–42.

Greene, M. R., & Oliva, A. (2010). High-Level Aftereffects to Global Scene Properties. Journal of Experimental Psychology, 36(6), 1430–1442.

Li, F. F., VanRullen, R., Koch, C., & Perona, P. (2002). Scene categorization in the near absence of attention. Proceedings of the National Academy of Sciences of the United States, 99(14), 9596–9601.

Prinz, J. (2012). The Conscious Brain: How Attention Engenders Experience. Oxford: OUP.

Siegel, S. (2012). The Content of Visual Experience. Oxford: OUP.

Thorpe, S., Fize, D., & Marlot, C. (1996). Speed of Processing in the Human Visual System. Nature, 381, 520–523.