A presentation I gave in Psychology of Music class at NYU on a study asking whether the ability to parse complex rhythms is learned or innate.

1. Metrical Categories in
Infancy and Adulthood
Erin E. Hannon and
Sandra E. Trehub
The study asks whether the ability to
detect structure-violating alterations to a
rhythmic pattern is learned or innate.

2. North American music uses simple meters based on groupings of
two, three or four beats. When North American musicians conceive
of complex meters, we usually think in terms of compounded simple
ones. To count in 11/8, we might think "3 + 3 + 3 + 2."
Bulgarian and Macedonian adults grow up with music in complex
meters, and feel these meters as complete units rather than
composites of simple meters. An example of Bulgarian 11/8
(Kopanitsa): http://www.youtube.com/watch?v=Giz3glVPm-I

3. Method
Fam: familiarization stimulus
SP: structure-preserving alteration
SV: structure-violating alteration
Grey dots show the drum
accompaniment to the musical
example. Alterations are in the
form of added notes, shown by
dashed lines.
The structure violation in the
simple-meter example is an extra
eighth note added to the bar of
4/4 time.
The structure violation in the
complex-meter example is an
extra eighth note added to the bar
of 7/8 time.

4. Findings
The top panel shows mean dissimilarity judgments of
North American adults. The middle panel shows the
same for Bulgarian and Macedonian adults. The bottom
panel shows infants' mean looking times. Simple-meter
results are on the left, and complex-meter results are on
the right.
North American adults had no difficulty telling the
difference between structure-preserving and structure-
violating alterations in simple meters. However, they
performed poorly in complex meters.
Unsurprisingly, Bulgarian and Macedonian adults
performed almost identically on tests with simple and
complex meters.
Against expectation, however, North American infants
performed more like Bulgarian and Macedonian adults
than like North American adults.

5. Analysis
One would naively guess that the ability to parse simple
meters is learned early in life, and that we learn more
complex metrical schemes by compounding simpler
ones. The experiment contradicts this assumption. It
appears that North Americans learn a bias toward simple
meters — or perhaps we forget how to parse complex
meters.
Do infants process rhythms differently than adults? Do
they just hear strings of beats without hierarchical
organization? Probably not. Infants demonstrate the
ability to parse other forms of musical organization. For
example, they can detect:
• subtle changes in duration and tempo
• isochronous (steady) versus nonisochronous
(unsteady) tone patterns
• auditory patterns generalized on the basis of
rhythmic structure
• unique rhythms on the basis of implied metrical
structure

6. Discussion Questions
Are adult biases in temporal pattern
processing learned during musical
enculturation?
Is there a relationship between our innate
ability to parse variations to metrical
schemes and our ability to pull words and
prosody from the speech stream, even
though everyone speaks differently?
How do we reorganize our temporal
pattern processing tools? How does
exposure to music "reprogram" us? More
generally, how do we figure out which
distinctions meaningful in our culture?
If I play a lot of Bulgarian music at home,
will Milo be able to groove to 11/8, or
does he need to hear it everywhere?