what are informative answers to the question, ‘why do zebras have stripes?’
TRANSCRIPT
Possible relationships of independent to dependent measure
2. Relatively direct causation• Properties:
– Tend to be easy to study– Robust to replication– Because relationship is direct and
data is robust, tends to be easier to build a predictive model for.
• Example:– Effect of breathing helium on vocal
pitch• Example:
– Dry air desiccates vocal folds (cf. Everett, Blasi & Roberts 2015)
Dependent measure
Independent measure
Possible relationships of independent to dependent measure
3. More indirect causation• Properties:
– More often context dependent– More often fails replication, until chain
of causation better understood– Theory, and requisite testing more
complex• Example:
– Effect of predators and evolution of physical properties• Lions and zebra stripes• Ground predators and loss of flight in
New Zealand
• Example:– Humidity and the development of
linguistic tone (Everett, Blasi & Roberts 2015)
Dependent measure
Independent measure
Possible relationships of independent to dependent measure
4. Shared cause• Properties:
– Direct causal theory more often difficult to articulate – which can be a clue…
– Positing joint cause can help generate new hypotheses about direct causes.
• Example: – correlation between
population size and grammatical complexity (Lupyan & Dale 2010)
Dependent measure
Independent measure
something else
Possible relationships of independent to dependent measure
5. Circular causation• Properties:
– Feedback can create large surface differences despite underlying sameness of process.
• Example: – Morpho-phonological relationships in
e.g., Turkish, Maltese, English• Learners tend to extend patterns that
already exist…• causing the pattern to become more
entrenched … (e.g. Hare & Elman 1995)
• Example: – Co-evolution of the lexicon and
phonology (Nettle 1998, Graff 2012, Wedel 2012)
Dependent measure
Independent measure
(often other things)
Possible relationships of independent to dependent measure
1. No broader predictive relationship; correlation is sample specific.• Properties:
– Due to sampling bias• Often through contingent historical
factors
– Not robust to replication– Often ‘discovered’, rather than
predicted by existing models• Example:
– Correlation between number of pirates and global temperature
Dependent measure
Independent measure
How does prior expectation influence the value of an observation?
‘Hypothesis discovery’ ‘Hypothesis testing’
Noticing an unexpected pattern in some dataset –
no obvious explanation
Noticing a pattern in some dataset – realizing it has a
plausible explanation
Confirmatory testing of an established model on a fresh,
well-controlled dataset
Initial testing and exploration of a priori theoretical predictions
in a dataset
How likely is a correlation meaningful?
• Null hypothesis: the distribution of sounds across the world’s languages is random with respect to geographic factors.
• ‘There is no correlation whatever between . . . any aspect of linguistic structure and the environment. Studying the structure of a language reveals absolutely nothing about either the people who speak it or the physical environment in which they live’.– Kaye, J. D. 1989 Phonology: a cognitive view. Hillsdale, NJ: Erlbaum, p.
48.• (But physical factors are thought to matter:)
• inverse correlation of rounding and height in vowels• correlation of stop voicing distinction with intra-oral volume
– typological probability of /d/ > /g/
• Tested hypothesis: lower atmospheric moisture correlates with lack of complex tone
• Prior evidence: it’s harder to produce precise pitch in drier air.
• Background assumption: Ceteris paribus, better cue quality correlates with a higher probability of sound contrast evolution. (e.g. Blevins 2004, etc)
Prior evidence for the hypothesis
• Desiccation of the vocal folds through inhalation of dry air quickly results in greater:– ‘Jitter’: variation in pitch– ‘Shimmer’: variation in amplitude
• Prior evidence for these effects exist from multiple kinds of experiments.
Data sources
• Tone and Location– World Atlas of Linguistic Structures (WALS)
• Somewhat areally, genetically balanced
– Phonotactics Database of the Australian National University (ANU)• exhaustive sample
• Mean Humidity– Kalnay E, et al. (1996) The NCEP/NCAR 40-Year Reanalysis
Project. Bulletin of the American Meteorological Society.– http://iridl.ldeo.columbia.eduSOURCES/.NOAA/.NCEP-
NCAR/.CDAS-1/.MONTHLY/.Diagnostic/.above_ground/
Mixed logistic regression, tone vs. no tone Estimate Std. Error z value Pr(>|z|)
(Intercept) -2.175044 0.001080 -2014 <2e-16 ***specH.mean 80.827246 0.001079 74882 <2e-16 ***
Mixed logistic regression, simple vs. complex tone (>3) Estimate Std. Error z value Pr(>|z|) (Intercept) -8.618 2.277 -3.784 0.000154 ***specH.mean 474.825 142.735 3.327 0.000879 ***
Mixed model results
Distance to the equator
Nettle, D. (1998). Explaining global patterns of language diversity. J. Anthropol. Archaeol., 17, 354–374.
Some blog posts on Humidity/ToneExplaining the stats of the tone and humidity paper:• http://www.replicatedtypo.com/tone-and-humidity/10207.html
Tone and humidity FAQ:• http://www.replicatedtypo.com/tone-and-humidity-faq/10286.html
Also interesting discussion:• http://dejonedge.blogspot.com/2015/01/my-first-post-publication-
review.html
• http://dejonedge.blogspot.com/2015/01/my-first-post-publication-review.html
• Null hypothesis: the distribution of sounds across the world’s languages is random with respect to geographic factors.
• Tested hypothesis: lower atmospheric pressure correlates with presence of ejectives.– Rationale: less effort is required to produce a sufficiently
high oral pressure for an ejective when ambient air-pressure is lower.
– Background assumption: Ceteris paribus, better cue quality correlates with a higher probability of sound contrast evolution.
Altitude and ejectivesCaleb Everett (2014). PLoS1 pp x-y
• Test: is there a correlation between the presence of ejectives and altitude?
• Datasets: – Ejectives: UPSID (ejectives: yes = 92/no = 475)– Location: WALS – Altitude: Google Earth + ArcGis + WALS
• Reported result:– There is a correlation between presence of
ejectives and altitude.
How does prior expectation influence the value of an observation?
‘Hypothesis discovery’ ‘Hypothesis testing’
Noticing an unexpected pattern in some dataset –
no obvious explanation
Noticing a pattern in some dataset – realizing it has a
plausible explanation
Confirmatory testing of an established model on a fresh,
well-controlled dataset
Initial testing and exploration of a priori theoretical predictions
in a dataset
How likely is a correlation meaningful?
Some blog posts on Altitude/Ejectives
• http://languagelog.ldc.upenn.edu/nll/?p=4685
• http://dlc.hypotheses.org/491• http://dlc.hypotheses.org/507• http://www.replicatedtypo.com/altitude-and-
ejectives-hypotheses-up-in-the-air/6324.html• http://swphonetics.com/2013/08/17/
corrcaus/
1. Structural Priming
Processing a syntactic structure -– makes subsequent processing of the same
structure faster– makes production of that structure more likely
Well-explored structures: Dative shiftPassive
Priming of Dative Shift
"... I don’t feel we should loan [them] [money]... I wish our leaders were really seeking the Lord on these things, and if we feel led to give
[a country] [money] to help them, fine”
give [money][to a country] vsgive [a country] [money]
(Jaeger & Snider 2007)
Structural Priming
• Operates across people within discourses• (Even operates across languages for similar
structures)• Significant priming effect persists for up to 10
sentences (Bock & Griffin 2000)
2. Verb phrase ellipsis (VPE)
Frankie [baked a pie]i and George did ____i too• Characterized by missing structure and lexical
material• Anaphoric relationship between the gap and some
other material• In order to reconstruct the intended meaning,
listener must – detect the gap– scan backwards/forwards through the discourse
context for possible filler.
Questions
• Is VPE structurally-primed?– It’s different from previously studied structures in
that it involves a long-distance dependency• If so, how long does it persist?