Aaron Schurger on One Step Closer to Consciousness

Sensory stimuli can be processed by the brain completely “under the radar” – without ever reaching your awareness. Of course, other neural activity in your brain IS contributing to your subjective reality. This raises the question, if I isolate a pattern of neural activity in your brain that bears information about a sensory stimulus, how do I know whether or not this neural activity is “inside” or “outside” of your awareness?

We already know that the activity tends to be more intense and longer lasting when it is part of your “stream of consciousness”, but we suspected that there was more to it than that. We used a method called “dichoptic color masking” to render visual objects invisible to the conscious mind, but still demonstrably processed by the brain. We used functional magnetic resonance imaging (fMRI) to infer patterns of brain activity in the temporal lobes while subjects looked at these images. Compared to the patterns of neural activity induced by “seen” stimuli, those induced by “unseen” stimuli varied much more erratically from one viewing to the next of the same kind of object (separated in time by tens of seconds), independent of any possible differences in the intensity of the neural response. We suspect that this is because neural activity patterns are stabilized when they “enter” awareness, by settling into a transient recurrent “agreement”, leaving non-conscious processes bickering on the sidelines. Further research will be required to bear this out.

Extract of the article in Science Reproducibility Distinguishes Conscious From Nonconscious Neural Representations (Aaron Schurger, Francisco Pereira, Anne Treisman, Jonathan D Cohen):

What qualifies a neural representation for a role in subjective experience? Previous evidence suggests that the duration and intensity of the neural response to a sensory stimulus are factors. We introduce another attribute—the reproducibility of a pattern of neural activity across different episodes—that predicts specific and measurable differences between conscious and nonconscious neural representations indepedently of duration and intensity…..

Read more in Science

About Aaron

grey Aaron Schurger on One Step Closer to Consciousness Aaron Schurger is Post-doctoral fellow, Research group of Prof. Stanislas Dehaene, INSERM U562 / NeuroSpin / CEA-Saclay, FRANCE

In response to the question below:

grey Aaron Schurger on One Step Closer to Consciousness

Comments

  1. What about using this as subliminal stimuli to re-train brains in pts with pain, but without them having to “do the work” of Recognise, for example? Watching someone move normally gives one’s own brain the message that “everything’s okay.” A pt with chronic arm pain, for example, might watch someone moving their arm normally. Or a pt with swelling and redness in his arm from CRPS might see pictures of arms of normal size and color.

    Would that be beneficial? Or, do you think the person would consciously need to focus on the stimuli, or would it need to be set up so that it looks like it’s the person’s actual arm, as in mirror therapy?

    aaron Reply:

    Great question – here’s Aaron’s response:

    This is an interesting question, but difficult for me to answer since the treatment of chronic pain is outside of my area of expertise. There may already exist some experimental work on the effect of subliminal stimuli on the supraliminal (conscious) sensation of pain – although I do no know of any. If I were to speculate – I tend to be an optimist – I would guess that subliminal stimuli, be they visual, auditory, tactile, or even olfactory, could have a lasting effect the areas of the brain that are involved in the experience of pain, and of somatic sensation in general (the insula would probably among the areas involved).

    Some researchers believe that the effects of subliminal (or “non-conscious”) stimuli are necessarily short-lived, but I am not one of them – there are striking examples in the literature of effects that can last for weeks or even months. However, the stimuli that we used in our experiment are not that easy to work with (requiring a stereoscope of some sort), and impose some limitations on what kind of objects one can recognize. I’ve attached an example of the stimuli (see the end of the article above).

    As you can see, you are limited to exactly two colors, and the two colors must be roughly isoluminant. Thus, the only kinds of images you can readily recognize in this form are simple line drawings, or simple icons (like the silhouette of a bird, or the typical symbols for “men’s room” and “ladies room” that you see in airports). The kind of visual images that you are talking about (what you might need to aid in the treatment of pain) would have to be full-color and reasonably high-resolution. For this purpose, if you want the stimuli to be subliminal, you might use another technique like masking.

    The question I’m left with is, if you are going to look at a number of images as part of a treatment regimen, why not “see” them? I guess I’m not sure what you mean by “doing the work” – if you’re going to look at them, you might as well “see” them. However, if it were to turn out that subliminally presented images have a stronger (or simply different) effect on pain than supraliminal images, well that would be fascinating – and maybe a valuable clinical tool. It certainly might be worth testing.

  2. The brain re-training treatments – graded motor imagery, mirror therapy, etc – are great, but require multiple sessions per day, every day, and doing them with attention and concentration. I was wondering about “subliminal” treatment – pts could get the benefit, but without “doing the work.”

    Aaron Reply:

    Ah, now I see what you mean by “doing the work”. Well, if you were to use subliminal visual stimuli, you might be able to get the benefit even if the patient doesn’t consciously see the images. The problem would be that the patient would still have to stare at a computer screen while the images were displayed – the only difference is that the patient would not consciously see the images. If the subliminal stimuli are to have any effect at all, the subject still has look at the screen. So you’d still have to do some work (staring at a screen) – and it would be more boring besides. If subliminal stimuli had a stronger effect and/or a faster-acting effect (you might be able to present them at a faster rate) then it would certainly seem worthwhile. It might be worth testing with some patients to see what kind of results you get, but you’d have to think carefully about how you’d do it, and what technique you would use to manipulate awareness (masking might be best). The more I think about it the more interesting it sounds: there may be some instances where the “conscious mind” mostly gets in the way, so it is at least conceivable that treatment with subliminal stimuli might actually work better in some instances. If I was set up to do this kind of work, I would be keen on trying it out (at least a pilot).

  3. Great conversation guys. I have just a quick comment: the theory that underpins graded motor imagery is that we use subthreshold excitement of M1 neurons via premotor neural mechanisms to ‘prime’ normal intracortical inhibition and thus refine M1 activations. It is just a theory that hasn’t been substantiated but i reckon it is a sensible one. With regards to using subliminal stimuli – this would seem akin to mirror neuron system use – we have considered this to be more conservative than implicit motor imagery (for you Aaron – this is what ‘Recognise’ is about) and we have used it in a few cases where left/right judgments (Recognise) increase symptoms. In each case, regularly watching someone else move – we used film of people doing things – was followed by implicit motor imagery which was then no longer a problem. I tend to think JUST doing ‘motor empathy’ or subliminal stuff would not have as strong an effect because I think we need to gradually expose them to threatening inputs and repeatedly to it to, indeed, train the brain. I might be wrong of course…..thanks so much to both of you for this v. interesting conversation – great work!