Monday, September 26, 2011

The Stopped Clock Illusion

Everyone can relate to this. You're in class, at work, waiting for something... you look at the clock and that first second that goes by seems to take forever. Then every second after that appears to progress normally. Why is that?

This is due to a phenomenon called saccadic masking or saccadic suppression. A saccade is the rapid movement of your eyes from one point of attention to another. To demonstrate this to yourself, hold out your two thumbs in front of you, and try to move your eyes smoothly from your right thumb to your left. You'll notice that your eyes don't move smoothly. Instead, they jump to points between your two thumbs along the way.

Saccades allow us to make a mental map of our surroundings and all the points of interest within it.  This is because the part of your retina directly behind your pupil, the fovea is packed with receptors that enhance visual acuity.

Cross-section of the eye, Wikimedia.

When you look around, your eyes don't span smoothly across the scene in front of you. Instead they move in saccades, quickly directing your fovea from one object of interest (the sharp corner of that table that you don't want to walk into) to another (that cute guy/girl waiting for you at the other end of the room). Saccades also occur when focusing on the details of a single image, as demonstrated by these eye movement traces of subjects as they examined the bust of Nefertiti.

Source: MIT

What you don't notice in between these saccades is well, anything.  The saccade itself is so fast that your brain doesn't have enough time to process the information coming to it to make a clear image.  A blurry image isn't too helpful and would probably just give you motion sickness.  In fact, the shaky "hand-held" camera effects in the movie Cloverfield did just that to many of its viewers.

So then what does your brain do with the information sent to it during a saccade?  Nothing; this is what is meant by the terms, saccadic suppression and saccadic masking mentioned earlier.  Even though the eyes are sending information to the brain, the brain does not process the information, leaving you effectively blind during a saccade. However, saccades are not so fast that you wouldn't notice the lapse in vision. What's going on? You don't actually perceive being blind during a saccade but you also don't see the blurry image, so what are you seeing?

It turns out that once you've fixed your fovea on an object, your brain actually tells you that you've been looking at it from the beginning of the saccade.  You don't notice this difference in timing at all, unless of course that object of your gaze actually keeps time.  So even though you're focused on the clock for only a second, your brain is telling you that you've been focusing on the clock for the 1,000 milliseconds it takes the second hand to move plus the time it took for your eyes to move to the clock.

On average, a saccade takes about 100 milliseconds, or about 10% of one second. So if you happen to look at a clock right at the beginning of a new second, it will appear to take 10% longer than normal, resulting in the famous illusion known as Chronostasis, or the stopped clock illusion.

Sunday, September 11, 2011

Lucid dreams


Most of the time, when we dream we are not consciously aware that we are dreaming.  Despite the often fantastic circumstances of the dream, we accept that the events and experiences that are happening to us are real.  At least until we wake up.

Lucid dreaming, or the awareness that one is dreaming, is a fairly well-known, and well-documented phenomenon.  Most people report having at least one lucid dream in their life, but for the most part they are considered to be very rare occurrences in the overall population.  However, lucid dreaming was not always a well-accepted fact of life, and of course is still contested by some sleep researchers today.

The term, "lucid dreaming" was originally coined by the Dutch psychiatrist, Frederik van Eeden in 1913,  but reports of lucid dreaming have been documented since Aristotle's time.  For the better part of the history of research on dreams and sleep many people believed that lucid dreams were not dreams at all, but were the result of brief moments of consciousness due to transitory awakenings that are common during REM sleep.

Then along came Alan Worsley.

Alan Worsley is a bit of a lucid dreaming celebrity in the field.  A graduate student in psychology, Worsley had been developing his own ability to dream lucidly.  He was able to plan experiments while awake, and then recall and carry out the protocol once dreaming.

During REM sleep, your body paralyzes the motor activity eminating from the spinal cord.  This is thought to be because during dreaming motor activities are initiated in the brain in response to dream stimuli, but then they are not propagated beyond the spinal cord so that this (usually) doesn't happen:
However, it is known that not all motor functions are cut off during dreaming.  The most obvious being the eye muscles (hence, Rapid Eye Movement) and respiratory muscles.  Alan Worsley used this information to signal to an observer in the lab that he was dreaming and aware of it by moving his eyes left and right a pre-agreed upon number of times.  By carrying out this procedure with no lapse in sleep activity (as monitored on an electroencephalogram (or EEG)), Worsley effectively proved that lucid dreaming is a physiological reality.

Since Worsely many people have become skilled in lucid dreaming, and indeed it has become accepted as a skill that most people can learn with practice and patience.  For most people, lucid dreams initiate when something in the dream is so outside the normal realm of reality that it becomes abundantly clear to the dreamer that he or she is dreaming.  You may think that something like a blue whale passing overhead like a blimp might be the sort of stimulus needed to induce that sort of awareness, but really it may in fact be something more mundane that suddenly jolts you into awareness.  In the clip from Waking Life that I posted a couple weeks ago, one of the characters suggests turning a light switch off and on.  In fact, this is a common method used by lucid dreamers to test waking vs. dreaming states of consciousness.  Worsley and other lucid dreamers often report that light levels are hard to adjust in dreams, so turning a light switch on and off is a quick and easy way to test if you are dreaming.  If it's a habit you can build in waking life, then you may find one day you try it and the results aren't what you expect, and from there it could be reasonable to conclude that you're dreaming.

Lucid dreaming can also be used as a valuable tool for studying consciousness and its properties both in the waking world and the dream world.  In particular, it's interesting to test what can be done in the dream world.  Since it exists purely in the mind, one would think that lucid dreaming allows you total control over the circumstances of your dream and you can essentially play God.  But in practice, most people seem to have limits to control over their dreams.  The light switch is one example, and reflections in a mirror are another.

In one study, dreamers were asked to find a mirror and view their reflection, and then to try and walk through the mirror.  Most participants could find the mirror and view their reflection with ease, however most participants also reported distortion in the image they saw in the mirror.  When they tried to walk through it, slightly less than half were successful in doing so.  What was on the other side varied from person to person.  One participant reported coming up from the bottom of a lake after entering the mirror.  Others reported moving through the mirror but then ending up back in the same room.

While this is cool and all, the fact still remains that most of the participants could not walk through the mirror.  Why?  It's a dream so anything should be possible.  That's something we generally believe even when dreaming non-lucidly.

The element of control may be in some way related to the level of lucidity.  Up until now I have been talking about lucid dreaming as a distinctly different type of dreaming from non-lucid dreaming.  But modern research shows that there is a continuum between states of lucidity in dreaming, and that this continuum affects the ability of the dreamer's control over the events of the dream.  Theoretically, if one can learn to dream lucidly, one could probably learn to master control over the events in the dream once lucidity is achieved.  And then who knows what you could be capable of.

But first, just try to turn the lights on and off.