Why Do Some Claim to Visually Experience Red?

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Why Do Some Claim to Visually Experience Red?

Suppose, as argued, it is untrue that humans visually experience red or any other categorical colour properties. Why have so many philosophers have assumed the opposite, and done so without argument?

Some time after learning to use a colour term like ‘red’ somewhat accurately, humans become faster and more accurate at distinguishing things which differ in whether they have the property denoted by that colour term (faster: \citealp{Bornstein:1984cb}; more accurate: \citealp[p.\ 22--7]{Roberson:1999rk}; not usually immediately: \citealp{Franklin:2005hp}). In fact, methods highly similar to those which indicate the absence of appearances do reveal that these properties affect speed and accuracy of discrimination (\citealp{witzel:2014_categorical}). As discrimination of these colour properties depends on pre-attentive processes which are automatic in some of the senses that perceptual processes are \citep{Daoutis:2006ij,clifford_color_2010}, the abilities to discriminate may intuitively give rise to the impression that properties like \emph{red} affect how things appear.

why?

‘If someone with normal color vision looks at a tomato in good light, the tomato will appear to have a distinctive property—a property that strawberries and cherries also appear to have, and which we call ‘red’ in English’

(Byrne & Hilbert 2003, p. 4)

Recall the argument. What we have established does not necessarily contradict the first premise. It may contridict the last premise

1. The second sequence of sensory encounters, (b), differ from each other more in phenomenal character than the first sequence of sensory encounters, (a), differ from each other.

2. This difference in differences in phenomenal character is a fact in need of explanation.

3. The difference cannot be fully explained by appeal only to perceptual experiences as of particular shades.

4. The difference can be explained in terms of perceptual experiences as of categorical colour properties.

5. There is no better explanation of the difference.

I want to have a go at rejecting the fifth premise without rejecting the first premise ...

As I said, I want to have a go at rejecting the fifth premise without rejecting the first premise.

For an example of a category effect which is automatic, I need to introduce you to the odd-ball paradigm.

In the odd-ball paradigm, you see a series of things that are all the same; and then, unpredictably, you see something different.

We can use sensitivity to odd-balls to measure the difference between the two blues and the blue-green pair.

This is useful because odd-ball effects can be detected very early in visual processessing, before attention kicks in.

They allow us to probe automatic processes.

odd ball

...

Now suppose we play you an odd ball sequence. We want to know whether an automatic process picks up on the difference. And we want to know whether the automatic process picks up on the difference always or only when a category change is involved. To do this we need to measure an event-related potential called vMMN (which is short for visual mismatch negativity).

vMMN (visual mismatch negativity): an event-related potential thought to index pre-attentive change detection in the visual cortex

Now I need to explain what an event-related potential is.

An ERP like the vMMN stands to an overall EEG measurement a bit like the number 78 bus does to a collection of atoms.

While we're on methods, let's quickly talk about fMRI.

better spatial resolution
limited temporal resolution
subject can't move

So now we know what an event-related potential is, let's get back to the vMMN (visual mismatch negativity).

vMMN (visual mismatch negativity): an event-related potential thought to index pre-attentive change detection in the visual cortex

So let me show you a task that uses this odd-ball effect Fixate on this cross. And when you see the rectangle, press the space bar with both index fingers. That's it. Except that you also see a block of colour on every trial. You're instructed to ignore this block of colour. And generally that's easy because it's always the same colour. But just occasionally it's a different colour. In one condition, the usual and odd-ball colours are the blues. And in the other condition, the usual and odd-ball colours are cross-category, from blue-green. We're interested in whether there's a sign that your brain has detected the change when the odd ball colour occurs.

Put roughly, the results show that there is signal of pre-attentive change detection at around 100-200 milliseconds in the left visual field.

This is another way of presenting the same finding.

The vMMN is a DRN, but not all DRNs are vMMNs (see the paper).

Since this study \citep{clifford_color_2010}, \citet{he:2014_color} have challenged the results arguing that there is no vMMN when you control for irregularities in colour spaces using JNDs. However \citet{zhong:2015_shortterm} find a vMMN for newly trained categorical colour properties (which \citep{clifford:2012_neural}) didn’t.

why?

Mastering some colour words leads to

pre-attentive, automatic capacities to disciminate categorical colour properties

corresponding to those words.

Some time after (but not usually immediately after) learning to use a colour term like ‘red’ somewhat accurately, humans become faster and more accurate at distinguishing things which differ in whether they have the property denoted by that colour term (faster: \citealp{Bornstein:1984cb}; more accurate: \citealp[p.\ 22--7]{Roberson:1999rk}; not usually immediately: \citealp{Franklin:2005hp}). In fact, methods highly similar to those which indicate the absence of appearances do reveal that these properties affect speed and accuracy of discrimination (\citealp{witzel:2014_categorical}). As discrimination of these colour properties depends on pre-attentive processes which are automatic in some of the senses that perceptual processes are \citep{Daoutis:2006ij,clifford_color_2010}, the abilities to discriminate may intuitively give rise to the impression that properties like \emph{red} affect how things appear.

How?

How? How could these pre-attentive, automatic abilities to discriminate give rise to the impression that properties like \emph{red} affect how things appear?

Option 1: sensations

Option 1: The processes of discrimination modulate the overall phenomenal character of experience, and do so differently depending on which categorical colour properties are discriminated. On this option, we have something like a phenomenal signal of sameness and difference.

Option 2: misinterpretation

“Discriminable wavelengths seem to be categorized together because they appear perceptually similar”

(Bornstein 1987: 288-9).

Option 2: Philosophers (and perhaps others) intuitively (and incorrectly) assume that capacities to discriminate depend on how things visuall appear. That is, the intuitive (and incorrect) assumption is that I can visually distinguish categorical properties because things visually appear to have those categorical colour properties. (Compare \citep[pp.~288--9]{Bornstein:1987vv}: “Discriminable wavelengths seem to be categorized together because they appear perceptually similar”.)

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