What is time? We can't see it, hear it, smell it, taste it nor touch it and yet we know it exists. We know this because we depend on time so much in doing our daily activities. For example, you want to meet a friend for lunch. What's the first thing you ask? Where and what time? Let's say the friend answers the where but not the time. What then? You'd have no idea when your friend will come; you don't even know if he/she is coming on THAT day. For all you know your friend meant tomorrow or next week.
Humans aren't psychic (well, in the view of science we're not capable of being so), we can't predict what will happen in the next few seconds. And yet we move as if we do. When we dress up, we have all intention of going to work or school. When we wait at a certain place to meet up with friends, we expect them to come. When we go to our favorite store, we have full knowledge that we'd buy that chocolate bar we'd been craving for. All of this sureness in moving in the present with the unpredictable future in mind.
Time and space, at least in our brains, seem to be strongly linked to each other. This may be because one of the most common uses of our temporal mechanisms is to act out whatever needs to be done in a specific space. But where in our brain exactly does this all happen? Research has suggested that extrastriate visual areas, V5/MT and V3 are important for temporal processing. But how they're important is another thing.
The study I'm about to present aims to answer two questions.
1) What is the direct role of v5/MT in temporal discrimination?
2) Will the disruption of either the left or right parietal cortex interfere with time perception in the audio or visual domain?
Before the actual study, participants were subject to repetitive transcranial magnetic stimulation (rTMS) while performing five tasks. Four of which tested temporal discrimination of moving visual, static visual and auditory stimuli and one which became the control task. This was to get a general view of how the brain works when presented with the stimuli. After this, the participants were subject to the real experiment.
Experiment 1
Participants were presented with stimuli on a 19-inch color monitor. What was presented to them was an array of yellow dots in a black background. This was presented twice. Participants were asked to point out which of the two arrays had a longer duration.
Experiment 2
Same as Experiment 1 only this time the dots weren't moving.
Experiment 3
The stimuli presented were two vertical columns consisting of twelve dots each. The columns outlined a "path" (the target). In "absent" trials, the dots were displayed randomly. Participants were asked whether they saw the "path" in the first array or in the second array.
Experiment 4
Same as Experiment 1 and 2 only difference being that the participants were exposed to single auditory tones when presented with the intervals.
Experiment 5
Same as Experiment 4 only with a different time duration.
The researchers found out that when TMS was applied in the V5/MT or the right inferior parietal cortex (IPC), temporal discrimination of moving stimuli was impaired and greater differences between the two arrays mentioned earlier were needed to reach 75% accuracy. This meant that the effect of TMS increased uncertainty response but not the perception of time becoming longer or shorter. This determined that V5/MT and IPC are both independently important in the temporal discri
mination of moving stimuli. The results were the same for Experiment 2. It suggests that V5/MT might be involved in low-level visual timing. As for the auditory stimuli, there was no significant effect of V5/MT.Based on these results, the researchers concluded that V5/MT had a role in both temporal and spatial vision specific to visual modality. They also showed that the right, and not the left, posterior parietal cortex is responsible for discrimination of visual and auditory durations. It also shows that two models may be responsible for perception of time in the brain. It may be that timing is either centered in one part of the brain or distributed along those areas that are capable of temporal processing and that these areas are involved in task, modality and lengths of duration used. This research also showed that time may be an important factor for degenerate representation in the brain.
Okay I admit the entry is rather technical. It does concern the brain after all and what better way to explain the brain than through pure technicality. The brain is, after all, something we shouldn't mess around with thus we need to explain it in an objective manner. As for the how this study has struck me enough to write a blog entry about it...that may be subjective. My blog won't be used for future study after all.
Moving on. This research done by Walsh, et. al. explains how the very abstract concept of time is captured in our brains. Isn't it amazing that even something so complex is not enough in complexity so as to not be comprehended by that 3 pound mush that compromised 2% of our body weight. Wow, makes me realize that all of us are all brawn and almost no brain. Anyway. The study showed where in our brains exactly time is processed and how it's processed. At least, visually and auditory for the most part. This processing happens mostly in the right posterior parietal cortex which is known to be responsible in representing the different parts of space thus proving that time and space are intertwined in our noggins. It's responsible for the determination of vision for action (ehem accordance) and spatial vision. Basically how we perceive and act on the world in a definite time and space. Who knew our brains could operationalize such a vague and abstract concept that determines so much in our lives? Hey, in a way, we may even be kinda sorta psychic. With time as our crystal ball. Isn't that SO COOL??
Okay, that's as much as I can glean from the experiment without becoming a bore. For more information on how the time-space continuum works, please contact Einstein from the grave. Or my Physics 71 professor. :)
Reference:
Bahrami, B., Bueti, D., & Walsh, V. (2008). Sensory and association cortex in time perception. Journal of Cognitive Neuroscience. 20, 6, p1054-1062.
No comments:
Post a Comment