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For example, let's say I have a friend sprinting a 50m distance and that friend wants me to time the race, but I don't have a stopwatch so I have to count "manually". Can I count while simultaneously thinking about how she'll do and while wondering what I'm going to have for dinner?

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I'm interested in dreaming, and there are instances where a dreamer is engrossed in the dream, while also analyzing the dream. These activities are done at the same time. I cannot comment on the waking consciousness. – Alex Stone Oct 9 '12 at 4:30
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Parallel processes are often studied in a so called 'dual task' paradigm, where participants are drawing a picture and reciting a poem or, as in your example, counting and thinking about other things. Often this method is used to demonstrate limits in attention and find insights into how the brain works (in a serial versus parallel manner). Training is an important factor in this question. It has been shown that with a sufficient amount of training a lot of tasks can be done parallel very well - so if you sit there long enough and automize the counting the rest will follow.

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I can write on the board while teaching and say something entirely different at the same time. It doesn't always go well, but I can. Millions of people drive a car while singing, or conversing. Walk and chew gum at the same time... examples are endless. – no comprende Jan 12 at 0:37

I have to partly disagree with schultem here-- he is right that the dual task paradigm is used to study multitasking, but the idea that we can truly do two cognitive tasks at the same time is still contentious. In particular, the opposing view might say that we can't really do two cognitive processes at the same time, but we are in fact switching between the two tasks very rapidly. To make a an analogy, consider a computer with a single-core CPU: although behaviorally it seems like you are running multiple processes at the same time, all applications still depend on a single bottleneck.

One of the most well studied experimental paradigms for this domain is called the 'psychological refractory period', or PRP effect, which shows over 2,700 hits on google scholar.

A typical PRP task has the subject perform two reaction time tasks. For instance, he may have to hit a button with his right hand in response to a high pitched tone, and hit a button with his left hand in response to a low pitched tone. At the same time, he performs another concurrent task-- e.g., saying "blue" in response to a blue stimulus, and "green" in response to a green stimulus. By altering the stimulus onset asynchrony (SOA) (that is, the time from the start of the tone to the start of the visual stimuli), we can examine what operations people are able to perform in parallel.

Each task can be broken down into three components: perceptual analysis, response selection (cognitive), and response processing. A prominent theory emerging from the results of many PRP tasks is that we are able to truly do two operations in parallel if they require different modes: for instance, we can do perceptual analysis of a visual stimuli and auditory tone at the same time, and we can make a manual and vocal response at the same time, however we cannot do two response selections at the same time because they essentially require the same cognitive resources (single bottleneck).

enter image description here

This image from wikipedia describes what I'm talking about. The response selection from the second task must wait for the response selection from the first task to finish before it begins. The result is that, at short SOA, the total time taken to respond to both stimuli is the same-- as long as perceptual analysis of the second task ends before the response selection from the first task.

So in sum, yes, it might be possible to do the two tasks you are talking about in parallel, especially with practice. But on a more fundamental level, you may really just be doing very rapid multitasking. If you're interested in this theory, you may also want to read about threaded cognition, which demonstrates this effect for complex tasks.

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Thanks for your repsonse. – schultem Dec 7 '12 at 21:28
Thanks for your response. Here is a paper that shows within a PRP paradigm that indeed parallel and serial processes exist. While I am not an expert in this area, this seems to be some interesting evidence for both processes. – schultem Dec 7 '12 at 21:29
yes, that seems in line with my view. here's another good modeling paper that espouses the same view: Byrne & Anderson (2001) – Jeff Dec 7 '12 at 21:36
It has been shown that if the tasks are segregated into a stereotypically "left brain" one and "right brain" one, then it is not hard or involve multitasking. We have two hemispheres for a very good reason. Brain-divided patients show strong evidence of two entire threads of consciousness, which is clearly not multitasking. But everyone shows signs of multiple threads of awareness in their mental activity, if you just look for it. – no comprende Jan 12 at 0:42
there really aren't "left brain" and "right brain" tasks though. split-brain patients don't reflect typical brain functioning. – Jeff Jan 12 at 1:24

I experience thinking two different things at the same time, but not on purpose. It is very frustrating because sometimes if someone tries to divert my attention in a different way my two thoughts merge together to make room for a new one. At most I've thought of four different things at the same time. I can actually hear them quite well. They do happen at the same time, but there is always one thought that is much louder than the others. I don't think it's normal but i know of only a few people who experience it with me, one being my father.

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I experience this sometimes also, and most people do not think it is normal, although most people have it happen occasionally. I used to often have two different songs going on in my head at once, mixing together, and a third one coming in at times. It corresponded with a period of high creativity. – no comprende Jan 12 at 0:40

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