See this picture on the left? Try staring at the red circle for a moment, while paying attention to the gray ring. After a few seconds, doesn't it seem to that the circle fades away and you're left with just a red dot on a white background?You can thank Ignal Paul Vital Troxler for figuring that out: according to this Swiss philosopher, we now that that deliberately focusing on a fixed object causes other surround stationary objects to fade away.
Once you move your eyes, the gray circle should be visible again.
So what is actually going on here?
According to scientists, our eyes are always in motion and there's one type of motion we control, called saccades, such as when we deliberately scan a room, and one type we don't, microsaccades, which are just as crucial.
To understand why these microsaccades are so important in our visual perception, its also important to understand the concept of neural adaptation. Much like our nervous system adapts to the constant, unchanging stimulus of us wearing a watch or glasses, for example, the visual neurons would too adapt to constantly unchanging (static) visual stimulus. The article uses the example of a frog that cannot see a fly sitting on a wall but can see it as soon as the fly starts flying around. Our visual neurons aren't comparable to Kermit's but we also use these tiny subconscious movements, these microsaccades, to keep our visual neurons from "falling asleep" and causing stationary objects to drift away.
Research on micro-saccades is pretty niche but it isn't new — the article cites studies from the 1950's, one in particular where scientists created and fit a tiny projector over the eye in order for the visual scene to move with these micro-movements. They basically stabilised the retina, rendering the microsaccade motion useless. (If anyone reading this is a photography buff, you can think of microsaccades as the inverse of the Image Stabilizer found in some of the pricier lenses. What it does is much like what your eye does: it creates internal micro-movements within the lens to prevent image blur when shooting pictures while holding your camera, helping to combat the natural shaking of an unsteady photographer. But, if you inadvertently leave it on while shooting with a tripod, the stabilizer actually causes the blur. Our eyes want to do the opposite, they want to keep the image shaking.)
More modern research uses computer eye-tracking devices linked to a projector that moves the image you're looking at with the movement of your eyes; no more wearing scary suction cups over your eyes to participate in this type of study.
The article goes on to discuss the potential neuronal responses the micro-saccades are responsible for generating in the brain. (research with monkeys showed activation in the lateral geniculate nucleus and the primary visual cortex)
What I found particularly interesting about these micro-saccades is that researchers found that they may be useful in determining what it is we are actually paying attention in our visual field, even inadvertently. Research done at McGill University found that the direction of microsaccades was often biased in the direction where subjects were actually paying attention. Another, different, study showed that the frequency of the microsaccades affected visibility: the larger they were, the better the visibility. Or, as the article put it:
"microsaccade frequency can betray your attentional spotlight."This article seemed pretty spot on in discussing the purpose of microsaccades and sites of possible neuronal activation, but as a point of criticism, with the advent of "neuromarketing", I think its only a matter of time before labs that use EEG and eye movement tracking (usually of saccades, the bigger, intentional movements we make) will also claim to be able to track our microsaccades to tell their clients "what we're really thinking" without factouring into account that microsaccade activity correlates with other brain activity in an EEG reading (gamma band activity, to be specific).
http://www.scientificamerican.com/article.cfm?id=shifting-focus
In a way microsaccades establish a parallel between perception and attention. We often fall under the influence of neural adaptation and forget that we are either holding something or wearing something. What I am interested in is the line that is drawn between perception and attention. Am I oblivious to the watch that I am wearing due to inattention or neural adaptation? Where is this boundary defined? It is spooky to think that certain things temporarily can 'disappear' from reality just based on lack of attention and neural adaptation. Overall, microsaccades and attention are very interesting topics that emphasize that the world seen through our senses is very much different from the actual world that surrounds us.
ReplyDeleteFor people with Bálint's Syndrome, ocular apraxia is one of the symptoms that contributes to the overall disorder, which as we discussed in class, is rooted in problems with attention. Ocular apraxia, just as a refresher, describes a patient's difficulty with managing gaze fixation, both in being able to stay fixed on an object and in being able to shift away from an object (a saccadic eye movement).
ReplyDeleteI think it's a neat connection that wasn't brought up before - perhaps microsaccades, or lack thereof, associated with ocular apraxia play an important role in another key Bálint's Syndrome symptom, simultanagnosia. Simultanagnosia describes a patient's inability to perceive the visual scene as a whole. Lacking the ability to discriminate overlapping objects is one example of this. Often, the patient cannot even acknowledge the presence of objects in front of or beyond the point of fixation. All of a sudden, this seems to be an extreme case of what happened when I stared at the red dot in the picture above and watched the gray circle disappear.
On a hunch, I Google'd microsaccades and Bálint's Syndrome and come across this little nugget to share with everyone:
"Reappearance of the visual percept after intentional blinking in a patient with Balint's syndrome."
http://www.ncbi.nlm.nih.gov/pubmed/1827464
.......................well I'll be!
I have always thought that visual illusions were very cool. While I was reading the article my mind wandered to a question. What else don't we see? Our most important faculty can be compromised with a circle and a dot. But what about our cognition? we know that there are lots of brain bugs that can be taken advantage of.
ReplyDeleteI think it is really cool that scientists may be able to figure out what someone is paying attention to, even inadvertently, by tracking eye movement patterns.
This article is amazing! It reminds me of another psychology class (Psychology 240), the Psychology and Biology of Perception. We looked at optical illusions and learned how our mind plays tricks on us. This illusion is a great example of microsaccades and the role they play in everyday life. When I give my full attention to something like reading a book, watching t.v., or staring at the projector during a lecture, most things in my surrounding seem to disappear until I move my eyes around and they come back into my conscious attention. It would be overwhelming if our minds kept conscious attention of every aspect of the visual scene.
ReplyDelete