The syntax mode
Click on the 'Dynamic movies' tab and select the syntax mode. Note that the interval and
slide positions have changed, and that 'Draw lines' is now checked.

Move the time control to the later stages of song development, select duration for X and
pitch for Y axis. Set the color scheme to user defined and select red. Then click 'DVD
Play/Stop'. Instead of looking at the syllables as dots, we now look at the trajectories that
connect them in time. That is, the order of singing the song syllables is now represented
by lines that connect those syllables. When a short duration syllable is followed by a
longer duration syllable, SA+ will paint the line red, and when a long syllable is followed
by a shorter one, the line is blue. It is immediately apparent by the movie, that the song is
stereotyped; however, it is also easy to see drifts in the pattern. As shown by the black
arrows (these are not in the movie) the shape equivalent of this song is a triangle. Each
projection (using different features) will give a different view of this syntax patters,
obviously, some projections are nicer then others.


We can now explore the syntax development of this song. Moving the slider back to the
original setting, duration versus FM, shows nice transitions of syntax structure during
development as exemplified in the figure to your right. Note how
the blue and red 'streams' get separated during development as the
third song syllable appears, turning the shape into triangle.
Now say that you want to observe the possible effect of circadian
time on song syntax: selecting 'color by time of day' will present the
trajectories with circadian color, indicating that for some features
(e.g., pitch) evening (blue) and morning (red) trajectories differ
during early development.
Note that although we call this 'syntax mode' what you actually see
is not really syntax, but some combo display capturing both syntax
and feature (sort of phonetic) changes. We find this representation
particularly useful because there are reasons to believe that the
changes of feature structure (within a syllable) and changes of
syntax might be linked. For example, a prototype sound can give
rise to two different types of sounds (see details in Tchernichovski
et al 2001, sound differentiation in situ).
This is a good time to elaborate about the relations between the
observed clusters and the actual syllables produced by the bird. The
clusters are at best as robust as the segmentation method is, and
unfortunately, our current methods of segmentation, based on
amplitude and Wiener entropy thresholds are not always robust.
The most common type of measurement noise is inconsistency in
the segmentation of short attenuations. For example, if the 'real'
pattern of syllable is ABC,ABC,ABC… and the pause between B
and C is very short, SA+ might sometimes join B and C, to give an
additional 'combination cluster' that we shall call D. hence, what we observed as
ABC,AD,AD,ABC should actually be ABC,ABC,ABC… This problem, once detected, is
not too difficult to solve. For example we can re-segment the data (using the binary files
rather than the raw sound files) using a more aggressive criteria for partitioning sounds.
Next versions of SA+ will include some more sophisticated methods for addressing those
issues. Methods of detecting 'combination clusters' are described in chapter 7.
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