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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

1. 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