The experimental method in phonetics MA in Phonetics.
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Transcript of The experimental method in phonetics MA in Phonetics.
The experimental method in phonetics
MA in Phonetics
Objectives Understand principles of experimental method
Design/conduct a simple phonetics experiment Consider over Christmas vacation Discuss in 2nd seminar (week 1, Term 2) Make recordings
Learn some basics of instrumental analysis 3rd seminar (week 3, Term 2)
Present the results of your experiment, in both written and oral format 4th seminar (week 5, Term 2)
Types of phonetic studies
Descriptive E.g. measure vowel formants, duration of long and
short vowels, etc.
Experimental Hypothesis testing, e.g. does vowel duration
decrease as speech rate increases?
Why do we do experiments?
To test ideas, beliefs, hypotheses, claims of others etc. In principle, no appeals to prior or higher authorities are acceptable in scientific investigations.
In practise, because we try and test one idea at a time, we assume that the established body of scientific knowledge regarding all other questions is acceptable. Provisionally….
Scientific mindset
We start from a position of scepticism. This can help us to determine whether a hypothesis is amenable to further substantiation or refutation.
Often we test things that seem intuitively obvious because sometimes the obvious is not true
Some example hypotheses 1) Drinking alcohol impairs pronunciation.
2) During speech, articulators move from one position to another in the way that requires least effort.
These both seem intuitively sensible claims, but are they right?
Only through controlled experimentation can we know for sure
Might reveal fine nuances
Characteristics of experimental method
Allows us to study cause and effect (and correlations)
Allows us to control variables that are not of interest in order to isolate variable that IS of interest
Allows us to investigate a hypothesis
Hypotheses
A provisional supposition, often stating there is a causal relationship between 2 variables asserts that the value of one variable, the independent
variable (IV), at least partially determines that of another, the dependent variable (DV)
E.g. tickling students during class affects their performance in
exams watering plants makes them grow higher vowels are shorter the more syllables there are in the foot
Testing hypotheses
A hypothesis must be FALSIFIABLE
There should be a way to show the hypothesis is not wrong
This is the way the scientific method advances the discovery of knowledge
Theories hold until the are proved false So it’s important they can be proved false!
Controlled experiment
A planned procedure that gathers comparative data under controlled conditions.
Experimental group subjected to the variable we want to test and the control group is not exposed to that variable E.g. tickling; watering; more syllables…
The only variable that should be different between the two groups is the variable we want to test.
Comparative data
Tickling: hypothesis tested by comparing performance of people who have been tickled in class with that of people who have not
Plants: comparing height of plants that have been watered with that of plants that have not
Vowels: comparing duration of vowels in feet of differing syllable-count Control group? - Could be feet with minimum number of
syllables
Matching control and experimental groupOnly the independent variable differs
between these
Other characteristics should match as closely as possible, e.g.: Gender, age, experience of student Seed type, location planted.. Vowel type, position of vowel in relation to
phrase…
Independent variable
Controlled by investigator
Values determined before experiment is carried out, e.g.:
How long/often students are tickled How many times plants are watered How many syllables in the foot
Interactions An effect might have multiple, interacting causes:
Poor performance might be due to combination of being tickled; not doing homework and not getting enough sleep
Poor growth in plants might be due to combination of not being watered and being planted in stony soil
Shorter vowel duration might be due to combination of foot length; vowel type and speech rate
Begin by trying to isolate and manipulate factors individually, and holding other factors constant
Once we understand the effect of a single factor, we can investigate how it interacts with others
Dependent Variable
Measured during course of investigation
Performance in exams
Plant height
Vowel duration
Confounding variables
These are things that might affect our results but that we’re not interested in (at the moment)
E.g. some students might be more ticklish than others
Some plants might need more watering than others
Some vowel types might be more susceptible to shortening than others
Confounding variables introduced by experimental procedure
Differences in instructions given to participants Can be overcome by standardising instructions
and general recording procedure
Differences between participants Can be overcome through careful selection of
subjects
Experimental results
QuantitativeWe can MEASURE resultsThis allows us the possibility of performing
statistical tests
Should be as robust as possibleOne sample not enough: observational
conclusion too fragileTry to get as many data as possibleMakes statistical testing more meaningful
Drawing conclusions Strictly speaking, there are two possible outcomes to an
experiment1. Results support hypothesis2. Results do not support hypothesis
If they support: We can go on and add in other variables to see if they interact
If they do not support: We reframe our hypothesis to account for results we have
Either way, the goal is to constantly refine and advance our knowledge
Falsifying hypotheses
Results that support a hypothesis do not prove that it is true
We carry on subjecting hypothesis to more tests
Eventually, we may reach a high degree of confidence that the hypothesis is true (without actually proving it)
Results that do not support a hypothesis are still interesting, since they allow us to eliminate one hypothesis
Correlations
Sometimes, even if we don’t think there is a causal relationship, there may be a correlation between two variables
E.g. a study showed that children’s reading ability increases with shoe size Do we conclude from this that reading ability DEPENDS
on shoe size? Or that they both might depend on something else, I.e.
age?
Advantages of lab experiments
By allowing the deliberate manipulation of one variable, we can study cause and effect
Can be replicated by others
Usually yields quantitative (measurable) data that can be subject to statistical testing
Limitations of lab experiments
Artificiality
Biased or unrepresentative sampling
Ethics (less of an issue in phonetics than in e.g. Psychology)
Example experiment:
Growing Sunflowers
Farmer Fred wants to produce the tallest sunflowers.
He has 2 types of sunflower seed, called “HI-HO” and “GIANT”.
He does a pilot test to see which one grows the tallest.
He plants both seeds close to the farmhouse, and does not water them.
Variables
Dependent variable = ?
Independent variables
= ?
Height of sunflower
Seed type
Hypothesis
The hypothesis Fred has in his mind is that there will be a difference. That’s what motivating him to the experiment
However, it’s easier to state our hypothesis negatively, as a null hypothesis, since this is possible to falsify
Scientific method advances through falsifying hypotheses
Null hypothesis: that there is no discernible difference
between the two seed types
Results HI-HO outperforms GIANT
Proved the null hypothesis wrong. There IS a difference between the two types of seed
But can’t state categorically that ‘HI-HO is the best sunflower seed’
There may be many other factors that Fred did not take into account
We don’t have the full picture
0
50
100
150
200
250
HI-HO GIANT
Refining the test
Other factors may be affecting the growth of the sunflowers, e.g. position/soil type
Soil near farmhouse is clay, while soil at bottom of field is stony
Fred plants a second crop, planting both types of seed near the farmhouse and at the bottom of the field
Variables
Dependent variable = ?
Independent variables
= ?
Height of sunflower
Seed type, position/soil type
Hypothesis
The hypothesis Fred has in his mind is that there will be a difference between planting near the farmhouse and planting at the bottom of the field.
Once again, however, it’s easier to state our hypothesis negatively, as a null hypothesis, since this is possible to prove wrong (to falsify)
Null hypothesis: that there is no discernible difference between the
two positions
N.B. Even if we do not find a difference, we can still only accept the null hypothesis tentatively. We don’t know if there are other factors that are obscuring a difference, and one day someone might replicate the experiment and find a difference
Results Both HI-HO and GIANT are shorter at the bottom of the field
AND, HI-HO does not outperform GIANT in this position
Proves the null hypothesis wrong
There IS a difference between the 2 positions
0
50
100
150
200
250
farmhouse field
HI-HO
GIANT
Conclusions?
There is an INTERACTION between seed type and position
It appears as if the maximal growth is obtained from planting “HI-HO” seeds near the farmhouse
However, we have not proved this. We can go on refining the experiment to see if
other variables come into play
Third experiment
Fred remembers reading that sunflowers need water
This may be why flowers near the farmhouse grow better (soil there has more water to begin with)
He plants a third crop, to see what happens if he waters the seeds
Variables
Dependent variable = ?
Independent variables
= ?
Height of sunflower
Seed type, position/soil type, water
Hypothesis
The hypothesis Fred has in his mind is that watering will make a difference
Once again, however, it’s easier to state our hypothesis negatively, as a null hypothesis, since this is possible to prove wrong (to falsify)
Null hypothesis: that watering makes no
discernible difference
Results Sunflowers taller at
bottom of field
GIANT outperform HI-HO in this position
Watered GIANT near farmhouse are shortest
0
50
100
150
200
250
300
farmhouse field farmhouse field
no water water
HI-HO GIANT
Conclusions
Once we investigate more variables, we get a fuller picture.
With only one or two variables, it appeared the best seeds were “HI-HO”, and it appeared the optimal place was near the farmhouse.
However, by controlling more variables, we see there is an important interaction between seed type * position * water
Eliminating ‘noise’ in phonetics experiments
Very difficult to control all confounding variables
In practice, we concentrate on trying to control those that are likely to have greatest influence Eliminates alternative explanations for the hypothesised
effect
Keep conditions same where possible Applies to material (e.g. think of order of sentences) Applies to subjects (same instructions to all)
Co-variation
Often difficult in speech to vary one variable without varying another
E.g. intensity and duration tend to vary with vowel height
Some independent variables cannot be manipulated directly. E.g. Lindblom (1963) studied the effect of vowel duration on
target undershoot, but actually manipulated the stress and position of vowels to elicit a range of vowel durations.
Sequence of experimentation
Have an ideaBackground reading / discuss with othersDesign material and procedureRecordings (or perceptual tests, etc.)Analysis (auditory and/or instrumental;
statistical tests)Write-up and/or present findings
Projects
Pre-fortis clipping versus rhythmic clipping
Aspiration in unstressed syllables
Accent variation and change Regional Cross-generational
To think about over vacation Hypothesis (inc. lit. survey)
Dependent and independent variables
Control group vs experimental group
Material (and its presentation)
Subjects
Recording procedure
Measurements
Material: some tips phonetic environment
To avoid distortion of results (by introducing confounding variables)
To aid segmentation!
Linguistic factors Morphological, semantic, syntactic…
Position in the phrase Prosodic factors How many utterances needed? Disguising goal of experiment Fillers and randomisation
See how it’s done
The best way to get an idea of how experiments are designed, conducted and reported is to look at some journal articles:
Journal of Phonetics Journal of Acoustical Society of America Phonetica Journal of International Phonetic Association
Written reports
Abstract Introduction Background Method Results Discussion Conclusion References Appendix (test material)