Categorical Perception Flashcards
What is categorical perception?
Perception of different sensory phenomena as being qualitatively or categorically different
What is continuous perception?
The perception of different sensory phenomena as being located on a smooth continuum
When does categorical perception occur?
When a change in some variable along a continuum is not perceived as gradual, but as instances of discrete categories
Are within category differences important?
No, they are compressed
differences between categories are more important
What does categorical perception occur for?
Consonant continua - voice onset time, place of articulation
less evident for vowel continua
Why are stop consonants categorical?
Because of their place of articulation: either labial, alveolar or velar
and their manner in terms of articulation: voiced or voiceless
What is a voiced articulation?
No clear interruption of voicing
What is a voiceless articulation?
Involves a clear interruption of voicing
What does the place of articulation affect?
The transition of the formant
What is a formant?
Band of frequency which determines the phonetic quality of a vowel
What makes a sound B or P?
The duration of the silence
5ms - B
40ms - P
What has to occur for something to be defined categorically?
sharp phoneme boundary
discrimination peak at phoneme boundary
discrimination predicted from identification
What is a sharp phoneme boundary?
The point at which we hear one category to the next has to be sudden and abrupt - meet a threshold, then all switch to hearing another one
What is a discrimination peak at phoneme boundary?
Where things that vary by a small amount should sound very different - across a category, variation should be perceived as very different
What is discrimination predicted from identification?
They only sound different if identified as different phoneme
Categorical perception of the Ba/Da continuum
B and D are two voiced stops which differ by their place of articulation:
b is bilabial
d is alveolar
affects the slope of the second formant
Experimental evidence of CP
- Set up a continuum of sounds between two categories
2. Run an identification experiment
How do you synthesise sound between two categories?
By gradually changing the shape of the formant from upwards to downwards
What will an identification experiment show?
Everyone will hear Ba till you reach phoneme boundary then everyone starts hearing Da
What determines how much phonemic boundaries can vary by?
Individual differences and the language people have acquired throughout development - sometimes lead to people arguing about what they have heard
Are we good at discriminating between ordinary continua?
We are good at discriminating between frequency, loudness, brightness etc but not very good at labelling these differences
Why will there be a discrimination peak?
As one will be on one side on phonemic boundary and one will be on the other side
Are we good at discriminating between categorical perception?
No - we are better at labelling than discriminating
What does Liberman believe?
Categorical perception is an indicator of a special speech mode of perception that is distinctively human - phoneme is a result of human mapping auditory signal to articulatory positions - speech signal we hear is continuous but produce discreetly
Is categorical perception limited to speech?
If it is true that it is humans only, it should be but no
also shown by musical intervals
Is speech categorical perception unique to humans?
Identification - no, chinchillas and quails show the same VOT boundary as humans for the da, ta continuum - can be trained to respond differently
Discrimination - macaques show discrimination peaks at human VOT and place of articulation boundaries - suggests human speech exploits low level discontinuities in the way that vertebrate auditory systems represent sound
Is it innate?
Infants are born with the ability to make speech discriminations.. that they can’t make
animals make many of thee
adults and one year old infants lose the ability to make distinctions that their language doesn’t use
this is why it is difficult to acquire new languages
Why is it hard to acquire new languages?
Because adults lose the ability to make distinctions that their language doesn’t use - hard to perceive categories so hard to segment words into phonemes, different phonemes sound the same, so hard to articulate
How is CP acquired?
Reduction of perceptual sensitivity within native phoneme boundaries
sensitivity can be re-acquired with intensive training
What is a phone/phonetic sound?
A particular sound used by any language. e.g. the sound r or the sound l
2 different sounds
What is phoneme/phonemic sound?
A sound used in contrast to another in a particular language e.g. the category r as distinct from i - these are two phonemes in English but in Japanese they sound similar to listeners so as a consequence they don’t form 2 different phonemes
What are minimal pairs?
Phonemes in a particular language are defined by minimal pairs e.g. in English, lice and rice have a different meaning, because they contain different phonemes which constitute a minimal pair
there is no such thing as a minimal pair in Japan, so they have a single phoneme r
What does each language have?
Its own set of phonemic categories
English distinguishes r from l but Japan doesn’t
Tamil distinguishes from a dental t1 from an alveolar t2 but english doesn’t
Effect of experience on perception: what is the difference between ra/la?
The slope of the third formant
ra - up
la - down
If you run an experiment where you vary the slope of the third formant, what happens?
English listeners - perceive ra then suddenly la, there will be a discrimination peak in pairs which vary by a small amount of slope
Japan - Ra throughout, no peak
Iverson - synthetic stimuli
Listeners asked to identify and rate stimuli
American - everything to the left of phonetic boundary was heard as R. Things are separated but clustered at either side because they sound more similar
Japan - most perceive as R, only one as W
German - boundaries have shifted from Americans, not as clearly organised as Americans, some are to the left
all dependent on language exposed to as a child
What is the McGurk effect?
Speech perception is multimodal: integration of visual and auditory cues
Articulatory gestures influence auditory perception - brain is being articulated - top down influences
