segmenting nonsense

Segmenting Nonsense

Sanders, Newport & Neville (2002)

Ricardo Tabone LIN 7912

Background• Behavioural studies adults segment

continuous speech using several segmentation cues

• Problem: these studies cannot distinguish between fast segmentation and slower linguistic processing

• Speech segmentation has been studied in different groups of speakers (e.g. young infants, bilingual adults, etc) through different tasks

• There is a need for an experimental task that can be employed with all groups: Recording ERPs!

Background (cont)

• In continuous speech, initial syllables elicit larger negativity (N100) than medial syllables. (Sanders & Neville, in press)

• Initial and medial syllables were controlled for loudness, length and other acoustic characteristics.

• But…..

Research Question• Do N100 word-onset effects index

speech segmentation rather than acoustic characteristics pertaining to word boundaries?

• In other words, is speech segmentation affected by lexical processing of speech sounds?

Background (recap)

• In continuous speech, initial syllables elicit larger negativity (N100) than medial syllables.

• Initial and medial syllables were controlled for loudness, length and other acoustic characteristics.

• But…..• Interesting: Behavioural tests exposure to a

continuous stream of nonsense words allows listeners to learn to distinguish between nonsense words and part-word items

Experimental Design• Pre-test Subjects listened to 36 pairs of 3-

syllable Nonsense Words (NWs) and indicate which of the two items seemed more familiar.– Each pair consisted of one of the 6 NWs that would

be used later and one part-word items composed of the last syllable of a NW + the first 2 syllables from another word

• First Test Subjects listened to a continuous stream of the 6 NWs (babupu, bupada, dutaba, patubi, pidabu, tutibu), repeated randomly 200 times each – The words were generated by text-to-speech

synthesis and were sequenced without pauses:– Babupubupadababupudutabapatubipidabututibu

Experimental Design• Pre-test Subjects listened to 36 pairs of 3-

syllable Nonsense Words (NWs) and indicate which of the two items seemed more familiar.– Each pair consisted of one of the 6 NWs that would

be used later and one part-word items composed of the last syllable of a NW + the first 2 syllables from another word

• First Test Subjects listened to a continuous stream of the 6 NWs (babupu, bupada, dutaba, patubi, pidabu, tutibu), repeated randomly 200 times each – The words were generated by text-to-speech

synthesis and were sequenced without pauses:– Babupubupadababupudutabapatubipidabututibu

Experimental Design (cont)• ERPs were recorded during the first 14-minute

exposure.• Second Test Determined whether or not subjected

had learned to recognize words due to exposure alone• Next, training Subjects listened to the 6 NWs,

separated by 500ms, for 10 minutes, and separated by 100ms for an extra 10 minutes.– Speakers were asked repeated the word and were

presented with the text version on the screen.• Third Test Assessed which words subjects learned • Fouth Test ERPs were recorded during an extra 14-

minute exposure to the same babupubupadababu….• Firth Test Assessed which words subjects learned

Experimental Design (cont)• ERPs were recorded during the first 14-minute

exposure.• Second Test Determined whether or not subjected

had learned to recognize words due to exposure alone• Next, training Subjects listened to the 6 NWs,

separated by 500ms, for 10 minutes, and separated by 100ms for an extra 10 minutes.– Speakers were asked repeated the word and were

presented with the text version on the screen.• Third Test Assessed which words subjects learned • Fouth Test ERPs were recorded during an extra 14-

minute exposure to the same babupubupadababu….• Firth Test Assessed which words subjects learned

Participants• 18 participants• Right-handed• Monolingual English speakers

Results (Behavioural)• Second Test Subjects performed at ~50%

– exposure alone isn’t enough.• Third Test After training, participants

performed at 79.5%. Bingo!• Fifth Test Performance was measured

again after another 14-minute exposure. Nothing changed (79.2%)– No new words learned, no old words forgotten.

Results (Behavioural)• High correlation between individual performance

on post-training tests and the difference in N100 amplitude before and after training

ERPs Analysis• Divided the 18 participants into two groups:

– 9 High learners (M=55.1%) (M=90.7%)– 9 Low learners (M=52.2%) (M=67.9%)

• High Learners showed a significant effect of training on N100 amplitude, specially on medial and midline electrodes

High Learners

ERPs Analysis• Divided the 18 participants into two groups:

– 9 Low learners (M=55.1%) (M=90.7%)– 9 High learners (M=52.2%) (M=67.9%)

• High Learners showed a significant effect of training on N100 amplitude, specially on medial and midline electrodes

• Low Learners did not show a significant N100 effect

Low Learners

ERPs Analysis• Divided the 18 participants into two groups:

– 9 Low learners (M=55.1%) (M=90.7%)– 9 High learners (M=52.2%) (M=67.9%)

• High Learners showed a significant effect of training on N100 amplitude, specially on medial and midline electrodes

• Low Learners did not show a significant N100 effect

• All subjects displayed a N400 effect– It is possible that this effect might influence medial

and final syllables, since syllables last between 100ms to 300ms

High Learners

Low Learners

Discussion• The N100 effect is similar to the one observed

in processing English (Sanders & Neville, in press)

• Artificial Language learners (McCandliss, Posner & Givón, 1997) also display the same N400 effects while learning new words

• Japanese bilinguals also displayed a N400 effect and no N100 effect while listening to English (Sanders & Neville, in press)

Conclusion• The results indicate than N100 effects cannot

be solely explained on the basis of acoustic differences between initial and medial sounds

• Listeners who are better at segmenting speech show earlier segmentation effects

• Word-onsets effects are similar even when segmentation cues are very different – (e.g. NWs vs Native words)

• N100 represents an automatic process of segmentation, whereas N400 indicates a slower, lexically-orientated process of segmentation.

THE

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