What Causes Visual Illusions and Hallucinations?

[Lazernugget]

I've noticed this a lot, but I never though it was weird, so I'm deciding to ask PF.

Every once and a while, I'll just be sitting around, bored or contemplating the universe, when I'll stare at a blank object and start seeing little tiny circles with dots in the middle. Kinda like a molecule. Other times I'll see purple lines on things.

Also, when I'm trying to sleep sometimes, I'll put my arm sideways, and put my eyes on my arm. When I do this, I see a series of things. First its little lines moving and changing colors, in a black backround, then those will turn to string looking lines, that accumulate into grey ripples. Then I'll see a bunch of different sized blue dots.

I'm a pretty normal person, and I have 20-20 vision so I just think it's tricks on my eyes, but what do you think?

 

[Polyamorph]

I was curious about the very same thing a while back as sometimes I experience such things and found the following articles useful.

The first could be floaters (http://en.wikipedia.org/wiki/Floater), real tiny specks of protein strings suspended in the vitreous humour or blue field entoptic phenomenon (http://en.wikipedia.org/wiki/Blue_field_entoptic_phenomenon)

As for the second phenomenon, there are closed eye hallucinations (http://en.wikipedia.org/wiki/Closed-eye_hallucination) in which various shapes and even objects can be perceived.

 

[Lazernugget]

Cool! I'm not sure about the first two, but the third is EXACTLY what I see! Well, I think that mystery is solved for me. Thanks!

 

[Bloc911]

I am not a doctor but I learned a lot about how the eyes are constructed and function talking with my grandmother and grandfather whom are a nurse and MD. respectively. As to your first descriptions of dots and purple, yes they are floaters. Everyone has them to a greater or lesser degree. Staring at a blank page or screen would help you to be able to perceive them more clearly since there is less obstructing visual stimulation allowing greater perception of the floaters. As to why you see things when your eyes are closed and you have pressure from your arm or other part, that is why. The eyes are filled with fluid at pressure(Interocular pressure). The rods and cones which are situated on the back of the eye process light that hits them into electrical signals sent through the optic nerves to your brain where you brain interprets those signals as what you see. When your eyes are closed and you apply pressure there is some stimulation to the rods and cones which will send signals to your brain. The signal are not like normal signals you get when your eyes are open. They are cause by the pressure on you eyes and you see weird shapes and colors because you brain it trying to construct those signals like it does with normal light based signals from the rods and cones.
A Small experiment to test this for me was to in a darkened room, close one eye and cover the open eye with my hand. On the closed eye I gently applied some pressure with my finger tip. After a few moments in the closed eye with pressure applied I began to see light and patterns eventually with some color then, after a while it began to dissipate, like I was adjusting to the change in operating pressure.
Again I am not an MD., but this is the information I have gathered and observed for myself. I hope this helps.

 

[Bloc911]

And why doesn't spell check help crappy typists like me? Sorry about the typo's!

 

[Bloc911]

Blueman Group did a little show called Rod and Cones and give some info on it and a fairly cool show and music too. I thought it was nifty myself.

 

[Polyamorph]

as to why you see thing when your eyes are closed and you have pressure from your arm or other part, that is why. The eyes are filled with fluid at pressure. The rods and cones which are situated on the back of the eye process light that hits them into electrical signals sent through the optic nerves to your brain where you brain interprets those signals as what you see.

Yes this is true but you don't need to apply pressure to experience what are known as phosphenes (the experience of seeing light without light actually entering the eye). So it is one explanation but closed-eye hallucinations ( see this article http://en.wikipedia.org/wiki/Closed-eye_hallucination) can be observed without pressure, just with closed eyes in the dark (the OP's arm would help facilitate darkness).

P.S. You can edit your post to correct typos! :)

 

[Bloc911]

Thanks Polyamorph, I did a little edit. Also in the article it talked about closed-eye-visualizations and closed-eye-hallucinations. Since he said that when he put his arm sideways and put his head down with his eyes on his arm I figured that it was the interocular pressure induced closed-eye-visualization.

 

[olbab]

Yes this is true but ... see this article http://en.wikipedia.org/wiki/Closed-eye_hallucination)

I have experianced two sorts of these, only one is mentioned at wikipedia.
At night, usually, in bed, but not "half asleep": slowly drifting, swirling clouds, soft and faint blues and greens. If I "pay a little attention" to them the effect strengthens. I can "will" the formation of reds: these are more active, sometimes making quite interesting patterns. These sharper effects are within my sharpest vision area, presumably in the color vision area (was it rods, or cones? Oh well..)

The second sort occurred years ago and not often, on awakening before dawn. Dim but incredibly intricate images, extraordinary detail, sometimes photographic in reality (but never halucinogenic!). Always fast changing. These never referenced my memory, and were way beyond my imagination! Usually had the whole field filled with intricate small parts intermeshed, moving. If I tried to "follow" the action it would fade out even faster than usual.

My eye doc was totally uninterested.

Ol' Bab