Is 2 Seconds a Meaningful Time Scale?
It may be a complete coincidence that music loses its coherence on the same time scale as concepts lose their activation. There are two ways to work with the possibility of coincidence. One is to look at a range of other ways in which the mind puts things together and examine their decay properties. The other is to find some reason why 2 seconds might be an important and organizing time interval for human behavior and cognition. Here are a few examples of the research in my laboratory on the issue of universality:
Rhythm. The feeling of rhythm is a good example of Gestalt. When you tap out a beat there are two levels of awareness. There is the tap level of analysis which is like the vertices of the triangle and there is the feeling of rhythm which is like the experience of the triangle. The feeling of rhythm is an emergent experience. How slow can a person tap out a rhythm? This is hard to measure because you have to keep people from counting. It is always possible to subdivide any interval with precise counting. How does counting become precise? By putting the counts into an interval where the experience of rhythm survives. Try and tap out an rhythm where each beat is separated by 3 seconds. You will soon discover that you have no idea what 3 seconds is if you are prevented from counting (say by doing a secondary visual task which is what we did). When people try to tap out such a slow beat they end up meandering between 1 or 2 seconds and 4 or 5. They execute what is formally known as a random walk, slowly drifting faster and then slower. The adjacent graph gives an example from our experiment when a person was initially exposed to a beep that sounded every 3 seconds so that they would know the required interval to produce. The beep was then turned off and they had to press the space bar on the computer every 3 seconds, or what they thought was 3 seconds, 100 times. The graph shows their 3 second estimates in the order that they occurred.
This person soon lost track of what 3 seconds really is and started the wandering process. So the metronome actually serves two purposes. It prevents musicians from being given music that they could not hear and it prevents conductors from attempting to slow the music down to the point where nobody has any idea where the next beat is.
Synesthesia. One of the most compelling properties of music is the sense of space that it creates. This is literally true; I am not speaking in metaphor. Flutes and sopranos give a sense of elevation. Tubas, basses, and bassos give a sense of rootedness and depth. The sense we have of space when listening to music is another good example of emergence. There is no spatial height in the fluctuations in air pressure that are encoded as pitch. All of the spatial association is a pure product of neural processing in the mind of a perceiving animal. The ultimate reason for the spatial equivalence of pitch and height may be that they are both mapped into cortex in similar ways. By poking electrodes into the brains of unsuspecting animals psychologists have learned that neighboring pitches are processed in neighboring patches of auditory cortex and that neighboring parts of the retina are processed in neighboring parts of primary visual cortex. David Hubel and Torsten Weisel won the Nobel prize when they discovered these mapping properties in vision. This is an enormously interesting story and it may be the reason why notes can be put together into melodies in the first place. (Odors are not mapped not into cortex and I have never experienced an odor melody). At the level of cortical representation there may be little difference between a landscape and a tune.
We can use the height properties of pitch to do a very simple experiment in synesthesia. On each trial the participant hears either a low tone or a high tone. Some time later a dot is presented either at the top or at the bottom of the computer screen. The participant has to indicate with a keypress where the dot is located, top or bottom. When the tone precedes the dot by a second or less, people are invariable faster in the combinations (high tone, top of screen; low tone, bottom of screen). This is because the tone activates not only other tones, but also relative spatial position. However, when the dot is delayed by a couple of seconds, the advantage for space-pitch consistency disappears. The activation has decayed. The data from our experiment is shown in the adjacent figure.
Reaction time is here expressed with the mean removed and scaled by the overall variability (this is known as standardizing the data). The data in the left panel is for a time delay of 1/2 second. Negative scores indicate fast response times (faster than the mean to be exact). At this point the synesthesia is quite strong. The data in the right panel is for a time delay of 3 seconds. The error bars for all of this data overlap 0. For standardized data this indicates that all effects have been squashed. At 3 seconds out there is no activation of position by pitch height.
These simple experiments all illustrate a common point; organization in time has a threshold of about 2 seconds. Whenever two or more things are experienced in time, they have to be experienced within about a 2 second window for the emergent property to take hold. This is true for listening to music, for rhythmic movement, for trains of thought, and for synesthesia. The reason for this seems to come down to activation. Emergent properties such as melody happen when notes generate overlapping patterns of activation. If the activation dies out, there is no overlap, and there is no emergent contour. The metronome is limited to 40 bpm because this reflects the time period over which activation decays. Music just happens to be an enormously fine example of a place where the memory constraint applies.
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