Cognitive Daily

Yesterday’s post brings up an interesting question: How can you be unaware of having even seen an image, and yet be able to make reliable judgments about that image? That article is just one example of a variety of situations in which people can be unaware of seeing something, even immediately after being given a quick glimpse of it, yet behave as if they have seen it.

We discussed how visual images can be “masked” — flashed quickly and then followed by another image which is displayed for a longer period. Though observers had no conscious recollection of seeing faces, they still could make accurate judgments about the attractiveness of the faces they had seen. Earlier experiments have found that the ability of the skin to conduct electricity as well as responses in the amygdala region of the brain can be affected by these masked images, again, with no conscious knowledge on the part of the viewer of having seen the image.

So how can our skin and brain respond to the image without our being conscious of seeing it? A team led by J.S. Morris developed a procedure to find out. Since the amygdala is activated during a fear response, they first conditioned volunteers to be afraid of a black and white photo of man with an angry facial expression. They used photos of four different men, two angry, and two neutral. These photos flashed randomly on the screen at intervals of around 20 seconds. When one (and only one) of the angry photos was displayed, a 1-second burst of white noise was played at a level of 100 decibels (loud enough to make you jump, but not to hurt your ears). Each face was shown six times.

Next, the volunteers were placed in an MRI scanner, and shown the faces they had seen before. Half the time, the faces were masked, so they were not conscious of seeing them. The other half the time, the faces were flashed quickly without masking, so they were consciously perceived. Skin conductance was greater when the participants saw the masked images which they had previously been conditioned to fear. The brain scan revealed differences in blood flow in the right amygdala:

i-41f407dcc660e5323f3c56a208b07225-unseen.gif

Significantly more blood flow was observed in this region when the fear-inducing masked angry face was shown, compared to the non-fear-inducing masked angry face. So though participants were not aware of a difference in the images they were shown, their brains responded differently.

What Morris’s team found is that although the amygdala showed more activity during unseen fear-inducing faces, other areas of the brain associated with conscious visual activity were more active when the faces were seen. The mask appeared to disrupt the conscious visual process, but not the process that led to the fear reaction. The masked images were sensed — detected by the eye — but not perceived. The researchers identified a separate neural pathway which activates the amygdala, independently of visual cognition.

Morris’s group says that the pathway they identified is similar to the fear response in animals, which has been studied in more detail since more invasive procedures (surgery which systematically disables various neural pathways) can be used.

What’s especially striking about this experiment is how it shows two critical aspects of brain functioning: its modularity and its interconnectedness. Without the connection of the visual system to the amygdala, the fear response could not be activated as quickly. But the pathway doesn’t work in reverse: knowing we are fearful doesn’t tell us what we’ve seen. In that sense, the visual system and the amygdala are independent. This web of interconnections and dead ends is seamless — when we’re missing something, we don’t notice it at all, but when a feeling or thought such as fear or a visual representation is present, it is indistinguishable from any other.

Morris, J.S., Öhman, A., & Dolan, R.J., (1999, February). A subcortical pathway to the right amygala mediating “unseen” fear. Proceedings of the National Academy of Science, 96, 1680-1685.

Comments

  1. #1 SkookumPlanet
    April 12, 2006

    Six years ago I actually experienced what you’re describing. Here, with some atmosphere, is the story.

    It’s June and I’m again staying at a friend’s funky, comfortable, owner-built vacation home, way up a sand and gravel road in a small canyon in the high-desert forest of very rural, northern New Mexico. It’s literally Georgia O’Keefe country off the Abiquiu Reservoir. Spectacular location with a mini-mesa of salmon-colored sedimentary rock 200-feet from the front door.

    I am at the back door, standing in the sliding glass door-way, on the slide track, door wide open, drinking a morning wake-up cup of coffee. I face beautiful, mature, high forest and a small clearing for a back yard with a creek crickling on the far side. Straight in front, at my feet, is a 6-foot-long, slatted wooden walkway spanning the house’s dripline. It’s weathered to gray-brown, bare wood.

    Twice, I swing one leg forward, leaving the other on the jamb, to put my head two feet out from the house and into direct sun to gauge the coming day’s temperature. Then swing my leg back onto the jamb.

    The second time, without comprehending why, or even what, on the return swing my leg continues past the jamb, back into the house. As the momentum pulls my entire body back in, I reach up, grab the pull on the screen door, and slide it shut. It’s all one movement and takes about a second.

    Not until the screen door is three-quarters closed does my brain register what I had seen peripherally as I pushed back off the walkway. About a foot-and-a-half from the door, laying between two wood slats directly under where I’d swung my leg out twice, is a rattlesnake. Exact same color as the wood. They are plentiful in the immediate vicinity. It had probably spent the night there, and I watch it for 20 minutes before the shadows move, it warms up in the sun, and leaves.

    I had backed into the house and closed the screen door before my conscious brain had registered that my eyes had seen a rattler. Or more accurately, that I was nearly standing on top of it. At the time I thought that speed was from my body being trained by several months of walking everywhere with eyes on the ground and rattlesnakes in my brain. Your explanation makes more biological sense, although that body-brain training my have sensitized the ol’ amygdala.

    It was definitely a strange brain experience. One can begin to fathom how supernatural such experiences and brain adaptations would have seemed up until very recently.

    Fortunately, numerous as they are, rattlers aren’t as thick as hummingbirds up this gorgeous canyon, to segue to a more pleasant story denouement. One year at the New Mexico house, in early spring, I find myself standing, very still, near the hummingbird feeder, nearly ecstatic over 16 hummingbirds within arms reach of my head, 360 degrees around it! They stay and take turns feeding for 5, 10, 15 minutes, who knows, until I have to move too much. It is one of those occasions when our sense of time radically changes. Perhaps we’ll see a post someday on that cognitive phenomenon.

  2. #2 Johnpf
    April 12, 2006

    I think that what gives this phenomenon its “Wow, isn’t that a strange thing!?” factor is the automatic assumption that what we see is what we are conscious of. That, because we are so visual, because our sort of primates are so visual, we live so completely in a world of vision, and so when we have visual stuff going on that is not available to our conscious minds then it upsets us. Slightly. It makes us realize that perhaps the visual world we are so used to thinking we are the masters of does, in fact, still contain a lot of hidden and inaccessible stuff… inaccessible to our conscious minds, at least, which is what we consider to be ‘us’ rather than the other processes going on in our brain.
    Ignoring the ‘science’ of it, it’s fascinating to see the reaction that people have when presented with this phenomenon — and, in fact, to so many optical illusions — just because we’ve got a long evolutionary history of being visually-oriented organisms. I wonder if dogs, if they could speak and tell us their thoughts, would be obsessed with olfactory illusions… ?

  3. #3 SkookumPlanet
    April 12, 2006

    If I may . . .

    This isn’t my first style revision of a post. I wrote and posted the New Mexico rattlesnake piece late last night and went to bed realizing I’d missed a chance at an evocative element in the close. So here’s the last paragraphed revised into two –

    Fortunately, numerous as they are, rattlers aren’t as thick as hummingbirds up this gorgeous canyon, to segue to a more pleasant story denouement. One year at the New Mexico house, in early spring, I find myself standing, very still, near the hummingbird feeder, nearly ecstatic over 16 hummingbirds within arms reach of my head, 360 degrees around it! So many wings saturate the air with soft trilling, enrobe my ears and me with vibration, and fill my mind with wonder at what a world where birds buzz like big bugs.

    They stay and take turns feeding for 5, 10, 15 minutes, who knows, until I have to move too much. It is one of those occasions when our sense of time radically changes. Perhaps we’ll see a post someday on that cognitive phenomenon.

  4. #4 SkookumPlanet
    April 12, 2006

    Johnpf

    You bet. A dog’s thoughts on olfactory illusion, in Homer Simpson’s voice. “Heyyyyyyy! I smelled doughnuts. Where are the doughnuts? Do you have the doughnuts? Are they under the sofa? Up on the kitchen counter? Ohhhhh, who’s got the doughnuts?”

  5. #5 SkookumPlanet
    April 12, 2006

    .
    Same excerpt, more revision. I’ve taught various writing to various students. If you’re not interested in why I made the changes, skip the next paragraph.

    This helps readers better visualize the physical scene, corrects a “mistake”, enrobe *in* = dressed *in*, better defines how to read opening of the sentence, “So many wings…”, which was ambiguous until several words in, creates a better cadence for the finish, and with more info present word count is only +5, a “virtual cut” by tightening up syntax, always a good thing. The ending wonder expands, wonder “at” the world becomes implied gratitude “for” it, that I/we experience this event, this instant — Homo Sapiens are put in context. It’s more emotionally accurate and an ongoing theme in my nature writing, mostly what I write. The politics I do on blogs is responsibility I feel to the community.

    While numerous, rattlers aren’t as thick as hummingbirds up this gorgeous canyon, to segue to a more pleasant story denouement. It’s early spring at the New Mexico house. I’m standing very still under the eaves next to the hummingbird feeder, nearly ecstatic over 16 hummingbirds under there with me, an arm’s reach of my head, 360 degrees around it! So many wings they saturate the air with soft trilling, enrobe my ears and me in vibration, and fill me with the wonder of this world we have as ours, where birds buzz like big bugs.

    Editing — clever excuse to return to New Mexico throughout the day, don’t you think?
    .

  6. #6 Johnpf
    April 13, 2006

    That’s one aspect of an olfactory illusion, yeah, but I’m sure there must be more fascinating possible illusions that we are unaware of because we live so little within a smell-world. Probably aspects to smells that we can’t even think of, never mind try to capture that same feeling we get when we’re caught out by an optical illusion.
    Imagine being an organism that has less reliance on and less ability in its vision, let’s say something that doesn’t have such a fine-graded colour perception as we do, or doesn’t extrapolate 2d images into 3d objects (like when we see a trapezoid and perceive it as a square seen side-on with perspective). Give this creature something that relies on one of those visual-based illusions and, again if it could speak, it would probably just shrug, go “Meh” and wonder what all the fuss was about, simply because it doesn’t have the adaptive, automatic responses in its visual processing that we have evolved, so can’t experience the trick. Perhaps something like giving a prey-animal (with barely any stereo vision but great all-round vision) one of those stereo-optical “magic eye” things. It could probably look and look and stare forever and never ‘get’ it.
    Similarly with my hypothetical olfactory illusions. I’ll bet there are many aspects to smelling that we can’t even begin to imagine being tricked by simply because we don’t have that automatic, adaptive processing and don’t ‘think’ of the world in terms of smells.
    And that’s for a sense we *do* have. I can’t even begin to start contemplating an illusion based on, say, echo-location!

  7. #7 SkookumPlanet
    April 13, 2006

    Johnpf
    I have a poem, currently under complete overhaul [too abstract, doesn't scan], that suggests something similar. I’ll quote the stanza, from –

    Three Rainbows Lead a Squall Line Over Kachemak Bay
    . . . .
    Flowers are ultraviolet landing strips to butterflies. Led
    here through voids, birds and whales migrate Earth’s magnetic field.
    As artifacts do magnetic rainbows bloom in their minds?
    . . . .

    Yes, I saw three rainbows. New Mexico is beautiful, but Kachemak Bay surpasses everyplace, literally. Here’s my one-sentence evocation of Kachemak Bay. My second, post, final post of thread.

  8. #8 melatonin
    April 14, 2006

    Alain Pegna (who was at U Wales, Bangor, now back in Switzerland) found a very interesting related finding. A man who is technically blind was able to discriminate faces with positive and negative emotions above chance. Pegna suggests that the subcortical amygdala processing mediates this.

    cheers

The site is undergoing maintenance presently. Commenting has been disabled. Please check back later!