This is Paul Vershoor with Victor Laman. And Victor was just telling us about
his theory on consciousness,
in particular, setting up a contrast between his approach and what's also called global workspace.
And in some sense, the starting point for you was very much the statement like,
well, a correlation-based approach towards consciousness is just not going to
get us there. It's not enough.
So what's the problem with correlation?
Well, the problem with correlation is that you have to start out with a definition,
in this case of consciousness, of which you're sure of.
And then you can try to find out what that means on the neural side.
But of course, the real problem with consciousness is that we don't really know
on the psychological or introspective side what it really is.
We don't know what we are conscious of.
We don't know what consciousness really is. We don't know what it's used for.
Or we have actually no clue of what consciousness really is on the introspective,
psychological, behavioral side.
So then, of course, it also doesn't make any sense to just try and find a neural code of that.
So you mean, as long as we have no satisfying definition, we don't know what
we're correlating it with.
Yeah, that's the basic problem. So my stance would be to build a definition
using neuroscience, so to incorporate neuroscientific findings and neuroscientific theories inside,
neuroscientific arguments, you might even say, into building,
well, what you might call a new definition of consciousness,
which, of course, to some extent incorporates the old ideas we have about consciousness
from introspection and psychology, But to some extent also overrules or overrides
those intuitions by things we find out from neuroscience.
But isn't there a risk that this becomes circular? Because you're saying,
okay, we don't have a satisfying definition right now.
So let's try to develop one looking at more detail at neuroscience,
but it still would imply that you have to have at least an intuition,
which subset of phenomena you want to look at in order to develop this definition.
So what's that guideline now that helps you to identify these phenomena?
Yeah, the intuitions, to some extent, are fine. So, for example,
it's not problematic to have the intuition that, say, in deep sleep or in coma
or when you have a fully masked visual stimulus, that in those situations you
do not have conscious sensations. Right.
So that's an intuition which works fine. And also at the other extreme end,
when you have a visual stimulus being presented and someone says,
yes, I see this visual stimulus and I recognize who's in that picture,
et cetera, et cetera, there's also no real reason to doubt that in that case
people have conscious sensations.
But it's particularly in the middle, in the middle ground, where you go from
these clearly unconscious situations to these clearly conscious situations,
where we don't really know whether people are conscious.
We don't even know whether we self have conscious experiences.
And that's the situation where you have to extrapolate from these extremes towards
these situations in the middle.
But you can only do that properly if you take into account the neuroscience,
which goes along with it. All right, so you're saying there's like this gray
zone that has to disentangle, and that's where we have to include more constraints.
Constraints, of course, also from psychology and introspection,
but I think even more rigorously constraints from neuroscience.
To give an example, if we see all the essential characteristics of neuroscientific
processes which go along with situations where we clearly have a conscious person,
like when we report having a conscious person.
If we see all the key neural ingredients of that situation also happening in
situations where we have doubts about whether we have conscious sensation,
then we might conclude on the basis of that neuroscientific evidence alone that
in those cases we probably have conscious sensation simply because the neural
mechanisms are so similar in both situations.
Or at least are similar as long as, with respect to the essential ingredients of consciousness.
That we have to grant consciousness to situations which intuitively we might
think we don't have conscious sensations, like in neglect or when we suffer
from inattentional blindness or attentional blink.
Typically in situations where attention is removed, there you have,
This is in particular the situation where you have this gray zone that we don't
really know whether we have conscious sensations or not.
Right. So given that, this doesn't explain why you use change blindness as one
of your paradigms or not.
Yeah, so we use change blindness to a large extent,
showing that, on the one hand, if you take the change blindness results per
se, you have the inclination to think that consciousness is very limited,
limited only to what you attend to, that you only see a couple of objects at
the same time, maybe two or three or four.
Whereas when you do the change blindness experiment in a different way, using the, let's say,
the iconic memory version of the experiment image where you present a cue in
between the first image and the second image you will see that there is at least
evidence that people have a much richer representation somewhere inside their
heads the only thing is we don't really know whether that is a conscious representation,
now and in tune trying to find out whether that is a conscious that rich representation
is a conscious representation you could use neuroscience to try and find out
whether all the essential potential ingredients for consciousness that you do
find in situations where consciousness is unequivocal,
whether you also find those in this rich representation,
iconic representation, and then conclude, well, apparently, even though it's
uncertain behaviorally and introspectively whether there's consciousness there,
while we are sort of forced to conclude based on neuroscience that indeed people
do have a conscious sensation there,
and that as a result of that we are forced
to conclude that consciousness is not limited and only limited to what attention
is focusing on and limited in respect of that it only holds a few objects but
that it's It's much richer than indeed you perceive a whole scene all at once.
Are you not actually posing two questions? On the one hand, it would be like,
what's the content of memory and under what conditions and which aspects of
memory are accessible to conscious experience?
Well, you do the experiments. In the way you do the experiments,
you are addressing memory. That's correct.
But, of course, what that tells you is what the content of consciousness is,
at the moment you look, because it's very difficult to really know what the
content of consciousness is at the very now, at the moment that you look.
So the only way to go about that is ask subjects what they saw or when you've
presented the stimulus.
And, of course, essentially that's always about memory. But what turns out to
be the case is that you have different forms of memory of a particular visual scene that you see.
So you have the working memory, which is limited to a couple of objects,
and then you have iconic memory, which is much more widespread and contains many more objects.
And these two sorts of memory are remnants of the two different representations
that you had while you were viewing the scene, While you were viewing the scene,
you probably also had a focused representation,
attention being focused on
a few objects which you could cognitively manipulate and things like that.
But at the same time, you also had a much richer representation containing many
more objects which you were not attending to and which you could not cognitively
manipulate and which is linked to this iconic memory trace.
So the memory traces tell you something about the representation that exists
at the moment that you look, which is, of course, the real question.
But in the case of change blindness, there might be, let's say,
at some level that change blindness becomes almost trivial.
I mean, there are, let's say, given that perception means that you have to compress,
You have to throw away, if you want, signals to get to a percept.
So in that process, of course, there will be, let's say, pieces of information,
objects disappearing from memory, possibly, or from consciousness,
because it's also a necessary ingredient of just being able to perceive the world at all.
So, from that perspective, you could argue, well, it's not a big surprise that
it is a finite set, both iconic memory,
but also then, let's say, your working memory for visual processing would be finite.
So, why then can this paradigm give you an additional insight into this interaction
between perception, attention, and consciousness?
Well, obviously, whenever you go from a physical stimulus falling on your retina
to representation in consciousness, there's some sort of compression going on
and some sort of interpretation of this.
You have things like visual illusions, which tell you that whatever is physically
out there is not translated in a direct way into your conscious percepts.
There's some things like memory and previous experience and all that thing going on.
But regardless of that, what remains is that apparently in that transition from
the physical stimulus to these mental representations,
you have, well, so to say, different representations, different stages.
You have a representation which is rich and detailed, which contains more or
less the whole scene, albeit in an interpreted fashion.
And then you have a representation which is related to the focus of attention, which is more limited.
So you have these different representations all sitting there at the same time inside your mind.
And the real unanswerable question, at
least unanswerable from an introspective and behavioral point of view
is which of these representations is is the
conscious one that's the real that's the
real problem and that's the thing which we cannot answer from
introspection or behavior right so now there you um to answer now that question
you you also are introducing a a fairly a specific uh picture on how perception
visual perception would work right according to a number of stages.
So what are these stages exactly and on the ground of what did you distinguish them?
Okay, so whenever a visual stimulus is presented to our eyes,
basically we go through four stages of cortical processing.
First you have, let's say, a fairly shallow processing, feed-forward processing
by early visual areas and maybe a couple of more high-level visual areas.
And then following that, if a stimulus is attended, you will have this feed-forward
processing penetrating all the way up to higher visual areas,
motor areas, prefrontal cortex, etc.
So those are the first two stages which are sort of automatically executed.
Feed-forward processing either in the shallow or in a more extensive deep fashion,
depending on the tension.
And then after that you have what I call stages three and four where you have
recurrent processing, which means higher level areas feeding back into lower
areas and then engaging in reentrant or recurrent processing.
And then also you can have these reentrant processes being either of a shallow
nature in the sense that they only involve, for example, a few visual areas
or that they grow more widespread when attention is allocated,
to the stimuli that evoke these processes.
But the reentrant interactions also include frontal parietal cortex and you
have what others would typically call global workspace ignition amplification.
Okay, so it's an incrementally more complex circuit we're looking at. Yeah, exactly.
Also bringing in more and more top-down information, higher-level cognitive information.
Well, I wouldn't put it that way, because already in the feed-forward activation,
you can reach high-level areas like the prefrontal cortex.
And we have done some experiments showing that when you have this feed-forward
activation of prefrontal cortex, that may activate cognitive functions like
inhibitory control or attention and things like that.
Which tells you that these feed-forward activations, which we think on the basis
of all kinds of experiments,
are not generating any conscious sensations, that these feed-forward activations
may still activate all sorts of cognitive functions like attention or cognitive
control, but nevertheless are unconscious.
And of course, similarly, you can have recurrent interactions interactions,
which are either penetrating deeply or not, and that means that you would have
conscious versions of either attention or cognitive control,
meaning that in this view consciousness and attention or consciousness and cognitive
control or any other cognitive function are essentially orthogonal,
meaning that you can have both unconscious attention and conscious attention,
that you can have both unconscious cognitive control and conscious is
conflict control but then in these these four phases
of processing what's the minimal configuration that
could give me a conscious percept yeah so i think the the evidence points to
the idea that the minimal configuration you need for having a conscious percept
is that you need to have re-entrant recurrent interactions so stages one and two which are.
Are entirely feed forward, even though a stage two process may reach prefrontal
areas, high level areas, that still will be an unconscious process in the sense
that it's not accompanied by any conscious sensation.
It's only when you go to stage three where you have reentrant interactions or
to stage four where you have widespread reentrant interactions,
including frontal parietal network, that you have conscious sensations.
That's the idea I'm pushing for.
But this seems to be a more necessary condition for consciousness,
and not a sufficient one.
Yeah, this whole necessary versus sufficient argument is not getting us anywhere
in the sense that you could always say that something is either necessary or
sufficient or not necessary or not sufficient.
What I'm trying to argue is that whenever you have random interactions,
you have a conscious sensation.
The only thing is that when these re-entrant interactions are limited to early
visual errors, you will have a visual sensation which is not linked to cognition,
not linked to reportability, so you cannot report it to the outside world,
you cannot store it in working memory, etc.
But you will still have a conscious sensation.
And of course, when these re-entrant interactions grow more widespread to stage
four, when they they incorporate frontal parietal,
network, then you will have a conscious sensation which is also reportable,
which you can cognitively manipulate, which you can attend to, etc.
Okay, so it means on the one extreme we can say, well, you don't necessarily
need a pure frontal engagement to have a conscious experience, right?
This is one consequence of what you're saying.
Yeah, that's certainly one of the important consequences.
That's the upper bound, if you want, but now at the lower bound,
Maybe their things are a bit more fuzzy because sometimes I would argue,
well, a red level of a primary visual area, I will have dense recurrent interactions
locally to the area and with thalamus and so on. So I have recurrence.
However, if I would only stimulate V1, as also some studies have shown,
I would not necessarily consciously experience that stimulus.
So, it seems that this recurrence of a certain, of a minimal recurrence of a
certain kind must be present to then lead to a conscious experience.
So, what's that minimal requirement on recurrence?
Yeah, there's probably some minimal requirement which we need to add to that,
if you like, definition of consciousness.
I'm not entirely sure what it should be. Maybe it has something to do with the
amount of complexity of the interactions, you know, a lot of Tononi and people
and proposals like that.
If you would ask me, basically, I would say that, you know, whenever you have
reentrant interactions between visual areas, you have some sort of visual percept.
Of course, it might be a very primitive visual percept, like,
you know, only seeing a glimmering of light without any cognition added to it,
without you really knowing what the object is, without you, you know,
erupt from any normal sense of vision that you would normally have.
But still it would be a conscious percept you know and the
only thing that is added when you when when these
re-entrant interactions incorporate more visual areas
let's say object selective areas or face selective areas or
motion selective areas what you add are more layers in terms of well essentially
how beautiful the the the visual sensation is you know we see you add colors
you add motion you add you add you add shape you add whether it's a face or not and stuff like that.
So all this gets added to the visual percept, but that doesn't make it a more
conscious visual percept.
It only makes it a ritual visual percept.
But in every case, it's a conscious visual percept.
The only thing is that when the recurrent iterations are very localized,
it's a fairly poor and sorry visual percept.
And in the other case, it's a rich and very beautiful one. Okay.
Now, in the data that you described, though, there was another aspect that came
to the foreground where you had these unconsciously perceived faces that you masked out.
Remember, you had these… You generated crosses from everything,
but actually, subconsciously, a face might have been detected.
When you looked at that data, it looked like the main distinguishing factor
was whether there was sustained activity or not.
That's true. So would you accept that as a second parameter where you could
say, well, maybe to become a consciously perceived stimulus,
I have to trigger sufficiently sustained activity to engage these recurrent
circuits sufficiently,
possibly even including frontal circuits, to construct the experience. Would you buy that?
Well, the short answer is no.
No, simply because, you know, experimentally, it's, of course,
very difficult to tease apart sustained activity and reentered or recurrent
activity because you cannot have recurrent activity without it being sustained.
Well, you might have sustained activity without it being recurrent,
but at least the other way around, it's very difficult to tease those two apart.
So you might argue, well, maybe it's just about the activity being sustained,
which is generating the conscious percept.
The only problem I have with that is that, you know, it doesn't explain anything to me.
Why would neural activity that's more sustained give you a conscious sensation, whereas.
Activity that is less sustained would not give you a concept.
That doesn't make any sense to me.
Well, on the other hand, the difference between recurrent and feed-forward processing
is so fundamental in the sense that recurrent activity will give you the integration
of information over different areas of the brain.
As I've proposed in the talk, it might also give you things like more synaptic
plasticity being engaged.
There are many fundamental differences between recurrent activity,
it will give you a higher complexity of the neural networks that are involved.
But there are so many fundamental differences between recurrent activity and
feedforward activity that I find some explanation in that being the difference
between conscious and unconscious processing,
which I totally do not find in short versus sustained activity.
But imagine I would be a global workspace person. Then in some sense,
I would agree with you on recurrent connectivity.
I would say, no, I have highly complex and differentiated and integrated global
interactions in these networks.
And then I could argue, and I need at the input side of that,
I need an activity of a certain duration to drive this global workspace sufficiently.
So if I have one of these masking tasks, so the stimulus gets suppressed,
I cannot drive the global workspace circuitry sufficiently. So therefore,
a conscious percept cannot emerge.
While if I have a more sustained activity, I can drive the global workspace
and develop the consciously experienced percept.
But what would be wrong with that argument?
Well, of course, no.
What you're saying now is that the conscious percept is not coming from the
sustained activity itself, but from the sustained activity driving something
else, in this case, global workspace activation.
So essentially what you're saying is that the conscious sensation comes from
the global workspace activation.
But the necessary requirement of that is sustained activity.
Well, what I've tried to point out in the presentation is that,
of course, you could hold the case that you only have constant sensation whenever
there's global workspace activity,
but there are a number of theoretical, scientific, and other problems with that,
such as that you know this entails that for some reason it's prefrontal cortex,
activity which is important for consciousness which doesn't seem to have any
explanatory power it's there's of course lots of evidence that you can have
prefrontal cortex activation without you having any conscious sensation so again
there's no real reason to assume that you have that you need to have prefrontal cortex activation,
for generating consciousness, or the other way around.
You can have prefrontal cortex activation without you clearly having any conscious sensation.
When you assume the global workspace activation to be essential for consciousness,
you always conflate consciousness with attention, you conflate consciousness
with cognitive control, and also you're not capable of dissociating consciousness
from a report about consciousness.
So there are lots of reasons why consciousness.
Saying that global workspace activation is the essential thing that you need
for having a conscious sensation, from a scientific point of view,
seems, well, misguided.
So that's an important part of your story, where you're saying,
well, global workspace is one view on conscious experience, and I disagree with
this view for a number of reasons that you now just summarized.
And my alternative proposal is the one of recurrent interaction of some kind.
So um but but
to what extent is your proposal not
also consistent with a possible alternative interpretation
of a global workspace because i could argue well these systems
you point your finger to are like uh still global workspaces but at a smaller
scale yeah not necessarily inconsistent yeah okay but of course if you know
if i if i discuss this with uh the real proponents of global workspace theory,
they explicitly excluded the possibility of global workspaces being possible at a more local scale.
Because indeed, you're right. If you would acknowledge that you can have global
workspace on a more local scale, let's say only visual cortex,
then of course it's totally similar to what I'm saying.
But for some reason, which by the way is a total mystery to me, uh.
Essential tenet of global workspace theory as it has been put forward in the
last couple of years is that it requires the global broadcasting of information
via these prefrontal parietal networks throughout the whole brain,
which is essentially different.
But that seems to be the sticky point, right? There's much more debate on whether
this frontal parietal network is a necessary ingredient of consciousness or sufficient even or not.
Because if you would leave out this component, you would happily agree on some
sort of adapted version of what you might call a workspace.
Sure. I wouldn't see any reason for calling it a workspace, though.
But, you know, scientists more easily use each other's toothbrush than each other's term.
But aside from that, yeah, why not? Okay. So from now on, you talk about the visual workspace.
Okay but then the other the other thing before
getting to the to the conclusions here um what i
found very interesting is that you also really started to to to push this notion
of feed forward and recurrent down to to to to uh the neural substrate to the
level of actually receptor types and so on yeah so so can you maybe explain
that a little bit yeah so let's say from From a theoretical point of view,
we had the, well, let's say hunch that there might be differences in the molecular
machinery that is used for feed-forward processing as opposed to recurrent processing.
And in particular, that recurrent processing, you know, because it satisfies
the HEP rule and stuff like that, would be more prone to induce processes related
to synaptic plasticity and MDA receptor activation and stuff like that.
So, we did some experiments to sort of verify this hunch, and indeed we found
that in monkey visual cortex.
The recurrent signals are almost abolished when you apply NMDA receptor blockers
like APV, while the feedforward signal is not.
And conversely, you can block the feed-forward signal by an empire receptor
blocker like CNQX, which doesn't interfere that much with the recurrent signals.
So indeed, pointing out that there might be different synaptic mechanisms related
to feed-forward and recurrent processing.
And that triggered the idea that maybe recurrent processing is much more related
to inducing synaptic plasticity, learning, in other words, changing your brain.
And then of course you know ultimately this could imply that the difference
between conscious and unconscious processing is that conscious processing changes
your brain because it induces synaptic plasticity whereas unconscious processing
does not change your brain which at least to me gives sort of a fundamental answer.
Hunch or intuition about what consciousness is
really about and what and what the difference is what the real
difference is between conscious and unconscious processing but but
would you be willing to to really say like well and necessary condition
for learning in the brain is is consciousness
yeah so uh you know
let's say a funny prediction of
that idea would be that there's no such thing as unconscious learning
uh which you know is already contradicted
by the existing literature well actually if
you look at it closely it's not because all the instances of unconscious
learning that i've come across are mostly about
what i would call inattentional learning which is something else
entirely uh so all the
instances where you find so-called unconscious learning are
in fact instances where uh you might
well you you can fairly well assume that
you still have these re-entrant processes going on on
a local scale although not at a global scale
so that indeed people are not able to report about these stimuli devoted to
learning but for example unconscious learning has never in my mind at least
been convincingly shown in
cases where you can really be sure that there is not that there is no uh.
Recurrent processing going on like for example when you have a fully masked
visual stimulus which is only evoked feedforward processing,
you will never find any learning related to such a fully masked stimulus.
It's only in cases where you rather manipulate attentional reportability where
you find so-called unconscious learning.
How about motor learning, like in conditioning or forms of learning dependent on the cerebellum?
I'm not an expert on that, so I'm going to take the 15 minutes.
They exist, I'm telling you.
Oh, you know, the cerebellum, that was already pointed out, of course, in various talks.
The cerebellum is a very strange system in the sense that even though you might
have recurrence there, there's still no... it's probably not associated with
conscious experiences. And it's...
I have nothing to say about the state of health. Yeah, it's too scary, you know?
Yeah. So to conclude, I have two questions for you.
On the one hand, you went on this trajectory actually being very closely to
the data, physiologists, getting data in monkey and other animals.
And now you're moving more to these really challenging questions in this domain of consciousness.
And given that experience what's what's
the the victor lama law you think we should all adhere to in
our study of the brain and consciousness well i
think there are two laws uh the first law is that you you cannot know what either
someone else or yourself is conscious of uh at any particular moment in time
you simply don't know what the content of consciousness is and of course the
upshot of that is that it's useless trying to find neural correlates of consciousness.
And I would say the second law is, sort of following from that,
of course, that we don't need neural correlates, but we need neural arguments
to tell us what consciousness really is.
And if I put all the neural arguments together, together, of course,
with psychological insights and introspective insights.
I have the strong idea that the fundamental ingredient for consciousness is recurrence.
So now, if five years from now, I go up to Amsterdam and I'm going to find you,
chase you down and ask you like, okay, Victor, five years back,
you made this prediction, I'm going to check with you whether it was right or wrong.
What's this one prediction you were willing to stick your neck out for today?
Day oh well one of the predictions would be
like the things we discussed about learning
uh this is this is something i
i i really like very much because you know the link between reentrant connections
and and mda receptor activation uh that's really putting some sort of fundamental
ground under this whole idea of what consciousness is about so uh i think we at At that point,
we will have proven that there's no such thing as really unconscious learning
and that you, for example,
that you only get, say, visual learning from inattention paradigms and not from
really, well, and not from masking paradigms, for example.
Wonderful. Victor Lowe, thank you very much for this interview. Well, you're welcome.