by Dan Tippens
Our Assistant Editor, Daniel Tippens, asks Professor Ned Block, of New York University, about his work on the relationship between phenomenal consciousness and access consciousness. This is part I of that interview, we will publish part II later this week.
SciSal: I first wanted to start with an introduction to the concept of consciousness. As you’ve written in several of your papers, you call it a “mongrel” concept. It has a lot of different meanings that people frequently conflate. And it’s really important to distinguish between them in order to make good conceptual advances. So, could you distinguish between some of these senses of consciousness before we go any further?
Block: So the one that I’m most interested in is what I call phenomenal consciousness, which some people cash out as the redness of red, what it’s like to see or smell or hear, that internal experience that you get when you have a sensation or images in your mind. That’s what I call phenomenal consciousness. Now, I think that’s something we share with animals — certainly other mammals. And you know I believe that it does not require language or much in the way of cognition — maybe nothing in the way of cognition.
Another sense of conscious and consciousness is the one in which we are conscious of things. We are conscious of our own thoughts. We can be conscious of our pains, of our perceptions. That involves some notion of monitoring, some feedback and maybe some awareness of yourself. So that is another notion. That’s called monitoring consciousness or self-consciousness.
Another idea is what I call access consciousness. And that’s when you have an episode of phenomenal consciousness and it is available to your cognitive systems. So you can think about it. You can reason about it. So you smell a certain smell — smoke. And that fact of your smelling smoke can be used by you to think about calling the fire department, or to think about investigating the source of the smoke. That’s what I call access consciousness.
So those three: phenomenal consciousness, monitoring consciousness and access consciousness I think are the three main ideas. And of course, you can’t figure out what something is in the brain until you make the distinctions you need to between really different fundamental phenomena. I think those are three fundamentally different phenomena, although they overlap and interact.
SciSal: I was hoping I could get you to say a little bit more about access consciousness before we go into phenomenal overflow. I remember when I first read about access consciousness, I kind of leaned too far onto the behavioral aspect. So when I thought of access consciousness, I thought of the ability to report — verbally report, or maybe write down something, perform some external action. However, this isn’t what is fundamental to access consciousness for you.
SciSal: Could you say a little bit more, to distinguish between just mere behavioral report and what you mean by access consciousness?
Block: Yeah. So let me say I think that report is a good first approximation to access consciousness. One important reason it’s not adequate is that animals have access consciousness. And you know by and large, they can’t report. So it’s the extent to which a phenomenal state is available to cognitive machinery. And so a mouse or a dog or a cat can be access conscious of a smell or something they see. And then a representation is sent to their machinery of reasoning and deciding, even if they can’t report it.
One very common idea is the idea of the neuronal global workspace. The main adherent of this view is a French group led by Stanislas Dehaene, who has a book that just recently came out on how consciousness works . Now, unfortunately, he thinks that all there is to consciousness is broadcasting in the global workplace. So he thinks consciousness is just access consciousness. He doesn’t really recognize phenomenal consciousness. Or when he does recognize it, he thinks that it can’t be studied scientifically. And the reason he thinks that is that after all, the main data for a theory of consciousness is what people say about their own conscious states. They give numerical ratings for how visible a stimulus is. They tell you what the content of their state is. Those are all features in access consciousness. So it seems to him that’s all you can study. He’s been arguing that for years. But one of the most interesting developments is that people have figured out how to study phenomenal consciousness. And I believe they have pretty much shown that phenomenal consciousness is something quite distinct from access consciousness.
SciSal: One thing that’s very crucial to the whole debate about phenomenal overflow is selective attention. It says on your website, at least, that you’re starting to write a book on it, given its importance. And I know that Wayne Wu just published a book recently on attention as well. It’s becoming a very hot topic in philosophy. Now, I was hoping we could just kind of discuss conceptually some things about selective attention before we go into your arguments. First of all, how would you define selective attention?
Block: Well, I think that what William James said about it is largely right. It involves both amplifying or focusing on representations and crucially suppressing other representations. So it’s a combination of amplification and inhibition, amplifying the things you’re attending to or the representations of the things you’re attending to and suppressing the things you’re not attending to. So it is a process in which that happens. And the clearest cases are visual attention.
Now, it complicates things a bit that there are three types. So there is spatial attention, in which you’re attending to an area of space. And then the evidence is that the attentional field there has what is known as a Mexican hat shape. A Mexican hat has a peak and then a dip, and then it goes up again. So the idea is there is a kind of amplification at the center and then inhibitions surrounding that center. And then it goes back to a higher level outside that. So spatial attention is thought to have that kind of shape. And that tells you since we’re not aware of that Mexican hat shape, we’re really not aware of very much of where we’re attending. And that is in itself an interesting thing. Then there is something that is often called object based attention, where we attend to an object. And the test of that is whether the attention spreads in that object — whether you’re faster to notice something in that object near where you’re attending as opposed to something in a different object. And then there is something called feature-based attention, which is probably the least well studied, in which you amplify all examples in your visual field of a certain feature, like a color for example.
SciSal: Is there a hierarchy between how they relate to one another in terms of when they’re deployed? So I remember thinking to myself that maybe objects just are — philosophically, at least — a bundle of properties, a bundle of features, right? So maybe you always deploy feature-based first and then object-based — or maybe spatial first. Could you tell us a little bit about how they may relate to one another?
Block: Yeah, I don’t think what you’re suggesting is right. What may be true is that object-based is a species of spatial attention. That could be. But the relations between them are not that well understood. I should say that there is also another distinction between what’s sometimes called bottom-up attention and top-down attention. So in bottom-up attention, you know, if there’s a noise [slams hand onto table] like, on one side, your attention will automatically be drawn to that noise. But also you can decide to pay attention to something else.
SciSal: Alright, now I was hoping we could come to the phenomenal overflow argument now that we’re kind of situated a little bit with the terminology. So first of all, could you tell us generally what the phenomenal overflow claim is — what the rich view of consciousness is that you defend?
Block: Yeah, right. So I guess first of all, it’s based on the idea that people often have that they have a very rich visual field, conscious of many things at a time and that you lose your kind of cognitive grip on most of them. So there’s just a constant, you know, constantly evolving visual world in front of you. And you can only take in cognitively a few of those things. And that sort of intuitive idea is verified experimentally by a number of ways. Probably the technique that has been the most useful is the study of what is called iconic memory. And that was known even a hundred years ago and maybe even much longer ago. When you see you get a brief stimulus, and then even after the stimulus goes off, people have a mental image of many of the items.
And this was first demonstrated experimentally by Sperling in 1960. And what he showed is you can have a grid of letters — say, 12 letters, three rows of four. And if you showed it to people briefly, people could report three or four of those letters. But they said that they had a mental image of the whole grid. And then he tested this by giving them a tone — a high tone for the top row, a medium tone for the middle row and a low tone for the bottom row. And if you show them the image — the stimulus — and then after it went off, if you gave them the medium tone, they could report three or four letters from that row. This is called partial report superiority because you could report three or four from any given row — or if you’re not cued, just three or four. It’s like you have a cognitive apparatus that can take in three or four letters, even though there’s a lot more in your image. But once you take in those three or four, the image disappears .
SciSal: Could you say a little bit about how you respond to some of the common objections to this way of reading the results? A lot of people claim that an alternative interpretation is that there’s actually unconscious representation of most of the scene. And the cue, when you hear the tone, attracts your attention to the cued part of the scene and boosts that part into conscious awareness. This explanation gets the same partial report superiority result that you talked about without the claim that there is more consciously represented than what you had access to.
Block: Yeah, that’s right.
SciSal: Can you explain how you tend to respond to these objections or what you think of them?
Block: Yes. So first of all, let me say that I think you’re right — that that is the main objection. And the best proponent of that has been a guy at Oxford named Ian Phillips. The key issue is: does the attentional bottleneck come between unconscious perception and conscious perception? That’s his view. Or does the attentional bottleneck come after conscious perception, between conscious perception and cognition? That’s what I think. So I think that you consciously perceive many things and the bottleneck comes between conscious perception and cognition. You can only cognize a few of them. He thinks it’s unconscious perception that sees too many things. And you can only phenomenally appreciate a few. So those are the two views.
There have been quite a few experiments lately that support my side of the disagreement. One of them was done by an Israeli group headed by this person, which also has a philosopher on it, Jacobson. They did a version of Sperling which had letters of very many different colors. And the rows could either be low in color diversity, just from a third of the colors, or they could be high in color diversity, from all of the colors. And what they realized was that people were aware of the color diversity outside of the focus of attention. So they must have seen at least two colors because you can’t judge color diversity without having some grip on at least two colors. And they’re able to show that this had to be a conscious phenomenon.
They used three different tests. The most convincing one is they made the stimuli very hard to see. Some people were not aware of them consciously. And they found that people’s ability to do this depended on conscious perception of the grid. So it could not be unconscious. Although some other judgments could be made unconsciously, like the average color. People were able to have some appreciation of the average color even though they ranked it as the lowest visibility ranking, which is zero visibility. So diversity took conscious perception. That suggests we really do have conscious perception outside the focus of attention .
SciSal: I recall reading that paper, and one of the concerns I had when I read your paper arguing that this experiment you described with color diversity supports phenomenal overflow, was that you specified that it was only what is known as focal attention that was being deployed to the main task — focal attention being, I take it, attention to a small portion of your visual field, right?
Block: It’s a relatively small area of space, yeah.
SciSal: Yeah. However, I recall in a review of attention research learning about something called diffuse attention, which is kind of attention that is spread out over a large area. But it’s probably not going to give you as detailed information. Now, I can imagine someone saying, well isn’t it possible that there is diffuse attention even if not focal attention to the color parts of the scene…
SciSal: Which would allow you to still have conscious representation…
Block: Yes, yes, and that someone would be me, for example. I think that’s probably diffuse attention.
SciSal: Oh, okay.
Block: But here’s the thing. The key fact is that it’s that kind of diffuse attention that’s present in the regular Sperling phenomenon. The question is what’s in your consciousness? So whatever diffuse attention you apply to the whole visual field or to any of the un-cued rows, it’s the same diffuse attention that’s involved in the regular Sperling case when we are able to cognize only three or four of those items. The idea of the Usher experiment is that it shows that we are perceiving at least two items more than the items that we can report. So it suggests a richer phenomenology of perception.
SciSal: I see. So to summarize and make some things clear, what is really important about attention and its relationship to access is that attention seems to filter information into working memory. And then working memory is what is globally broadcast, i.e what is accessed, right?
Block: Right. That’s right.
SciSal: And I recall in one of your papers you mentioned that a lot of people think it’s between seven and nine characters that can be held in working memory because of a famous old experiment in the 1950s by George Miller, but it’s really something more like three or four items that can be stored in working memory. So to make it relevant, I take it the idea was if you can have more than three or four items that you are conscious of, then that shows that there’s more on your conscious perception than what is contained within working memory — i.e., what you have access to, regardless of which attentional mechanisms, diffuse or focal, filtered the four items into working memory.
Block: Yeah, that’s right. I should say, by the way, that it’s recently been shown, especially by my colleague across the street, that you really shouldn’t think of working memory as having three or four slots. But for the kinds of materials that are used in these experiments like, you know, letters and, you know, rectangles that can be oriented — for those things, you get the special case where there is a capacity of three or four items. It can be more for simpler items and less for more complex items. In fact, in the Usher experiment, it’s not really three or four, it’s really just three. And one of the key ideas here is that the things outside the cued row do not affect how many letters you can report in the central task. You can still report three whether or not they’re reporting color diversity.
[To be continued later this week]
Dan Tippens is Assistant Editor at Scientia Salon. He received his Bachelors of Arts in Philosophy at New York University. He is now a research technician at New York University School of Medicine in the S. Arthur Localio Laboratory.
Ned Block is Silver Professor of Philosophy, Psychology and Neural Science at New York University, where he arrived in 1996 from MIT. He works in philosophy of mind and foundations of neuroscience and cognitive science and is currently writing a book on attention. He is a past president of the Society for Philosophy and Psychology, a past Chair of the MIT Press Cognitive Science Board, and past President of the Association for the Scientific Study of Consciousness. The Philosophers’ Annual selected his papers as one of the “ten best” in 1983, 1990, 1995, 2002 and 2010.
 Consciousness and the Brain: Deciphering How the Brain Codes Our Thoughts, by S. Dehaene, Viking, 2014.
 Perceptual consciousness overflows cognitive access, by N. Block, Trends in Cognitive Sciences, 2011.
 Rich conscious perception outside focal attention, by N. Block, Trends in Cognitive Sciences, 2014.