# The Naked Scientists Forum

### Author Topic: How long does it take to process what we see?  (Read 3265 times)

#### Confused Robot

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##### How long does it take to process what we see?
« on: 11/01/2015 06:50:38 »
Hi Everyone,
I'm new to this kinda thing and was just wondering how long it would take for the brain to process a room?
Sorry if that's vague, I mean I've looked at a couple of reports. The latest says that it takes only 13 milliseconds ( newbielink:http://www.dailymail.co.uk/sciencetech/article-2542583/Scientists-record-fastest-time-human-image-takes-just-13-milliseconds.html [nonactive]), but that is just for an image so I'm not sure.
Others say it is 80 milliseconds for the brain to fully understand what it is looking at; newbielink:http://blogs.scientificamerican.com/observations/2011/09/15/time-on-the-brain-how-you-are-always-living-in-the-past-and-other-quirks-of-perception/ [nonactive]
Hence why I'm confused. Thanks to anyone who can help me with this, it is much appreciated.
Regards,
Confused Robot

#### CliffordK

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##### Re: How long does it take to process what we see?
« Reply #1 on: 11/01/2015 08:37:20 »
There are a number of different tasks that one might ask a subject to do.

Say I tell you to press a key every time the letter A appears.

Then if I present a bunch of images of a cow, dog, cat, the letter A, tree, etc...  Then it may not take much for you to respond positively for the letter A, even if you have several other non-letter images given to you in rapid succession (or the A was only presented briefly).

On the other hand, if I present you a screen with 3 letters on the screen (AXP), your short term memory should be able to handle it.  However, if your task is to watch for letters and then name all the letters you saw (no priming of the correct answer), it may be more difficult, especially if they are not all in the center of the screen.

Now, increase that to 4 numbers, presented 2 each on successive screens, again something STM should be able to handle, it may take longer still to process and store each image.

If you throw in reaction time (press A when you see A, press B when you see B, press space when neither is presented), and don't proceed until a letter is pressed, then the speed will even be slower.

One can, of course, seriously mess with the mind with the simple "Stroop effect".

Anyway, I have to wonder if one could do full scene processing with a 13ms presentation, but wouldn't be surprised if one could pick out certain features with a very short exposure time.

#### evan_au

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##### Re: How long does it take to process what we see?
« Reply #2 on: 11/01/2015 11:39:03 »
Quote from: CliffordK
Say I tell you to press a key every time the letter A appears.
I have done a similar experiment with a reaction timer when I was younger; I vaguely recall that I could usually get 250-270ms to press a button after a LED flash.

Quote from: Confused Robot
The latest says that it takes only 13 milliseconds
The 13ms sounds similar to the persistence of vision; successive frames on a TV screen are presented about 17-20ms apart (depending on the country) which your brain fuses into continuous motion; it also makes sense that this would be the shortest period of image presentation which can be recognized.

Quote from: Confused Robot
Others say it is 80 milliseconds
The 80ms is the tolerance of your brain to unsynchronised sight and sound. But if the sound is even a couple of ms ahead of the image, your brain registers this as unnatural, since it never occurs in the natural world.

Quote from: Confused Robot
milliseconds for the brain to fully understand what it is looking at?
I have heard that the conscious mind takes about 100ms to process sound, and around 300ms to process vision. This was highlighted by a case where, due to brain damage, a man started to hear the TV sound well ahead of the picture on the screen (even though everyone else thought it was fine). It turned out that a tumor(?) had desynchronized the conscious sound and image processing, so he was hearing the sound about 200ms ahead of the vision, which sounds very unnatural..

So I suggest that an image presented for just 13-20ms can be registered by the optic nerve, but it registers in the conscious mind only around 300ms later (in computer terms, we would call that a "pipelined architecture").

The brain also has unconscious paths for processing sight and sound, and these are thought to react more quickly than the conscious mind. This subconscious is probably partly programmable by the conscious mind, allowing you to respond to a letter "A" (or a LED, a tennis serve or a lion) in under 300ms, if you are expecting one.

#### dlorde

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##### Re: How long does it take to process what we see?
« Reply #3 on: 11/01/2015 19:52:23 »
It's thought that the process of conscious awareness of a single visual stimulus takes around 350-500ms, because when you test subjects with a stimulus that crosses the threshold for conscious awareness (i.e. they can report seeing the stimulus), there there will be three waves of brain activity, one positive, peaking at ~100ms, one negative, peaking at ~170ms, followed by a characteristic slow wave of activity (known as the P3 or P300 wave) that sweeps across the brain towards the frontal cortex, starting about 270-300ms after the stimulus, and peaking from 350-500ms later, before dying away, and often followed by a back wave of activity in the visual cortex.

If the stimulus is below conscious awareness, it will trigger only the first two waves, representing localised activity, mainly in the visual cortex, that dies away after 200-300ms.
[information taken from 'Consciousness and the Brain' by Stanislas Dehaene]

#### alancalverd

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##### Re: How long does it take to process what we see?
« Reply #4 on: 11/01/2015 20:00:59 »
Quote
In Flash Anzan, 15 numbers are flashed consecutively on a giant screen. Each number is between 100 and 999. The challenge is to add them up.

Simple, right? Except the numbers are flashed so fast you can barely read them.

I was at this year's championship to see Takeo Sasano, a school clerk in his 30s, break his own world record: he got the correct answer when the numbers were flashed in 1.70 seconds.

So assuming there is a gap of perhaps 10 ms between numbers, he was reading and processing a 3 digit number, storing the result, clearing his memory, and reloading the running total,  in 100 ms. Or just remembering a sequence of random numbers and adding them up later.

#### dlorde

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##### Re: How long does it take to process what we see?
« Reply #5 on: 11/01/2015 20:56:01 »
So assuming there is a gap of perhaps 10 ms between numbers, he was reading and processing a 3 digit number, storing the result, clearing his memory, and reloading the running total,  in 100 ms. Or just remembering a sequence of random numbers and adding them up later.
I imagine all this processing would be subliminal, using highly parallel System 1 processing. There's experimental evidence that simple arithmetic and simple contextual understanding of sentences can be done below the level of conscious awareness without any specific training. In this case, he would have trained himself to do this without having to consciously deliberate over it, and he'd probably be aware of the result (and, perhaps, some intermediate results) after they'd been processed.

Mind you, I'm impressed by the way some darts players can calculate not only the remaining score, but how to achieve that score in three darts or less, finishing on a double, with just a glance at the board...

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##### Re: How long does it take to process what we see?
« Reply #5 on: 11/01/2015 20:56:01 »