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)