BIBLIOGRAFÍA

The changes in speech production through the process o f phonological development have been well-documented and normal developmental patterns in phonology have been identified (Grunwell, 1985). In the pre­ school years, children will gradually modify their speech production and words become more adult-like, so that by the age o f about 5 years children’s speech production is mostly accurate. The development o f adult­ like speech production may be in part due to articulatory maturation, in that in early childhood, the requisite skills o f range and co-ordination o f oral movement are not yet fully developed (Stackhouse & Wells, 1997). Speech production may also mature as the phonological components o f lexical representations are more accurately and clearly defined (Vihman,

1996).

3.3 RA TIO N A LE F O R T H IS EX PE R IM E N T

Later experiments within this thesis require the use o f measures o f speech processing skills. The existing literature suggests differential performance across different measures o f auditory discrimination and speech production in children with normal and abnormal speech development. The

differences in speech processing demands, as analysed using the Stackhouse and Wells (1997) model, also suggest performance on tasks may differ. This experiment presents a range o f different speech production and auditory discrimination tasks to groups o f young children o f different ages, who are all developing normally. This will enable the evaluation o f performance on speech processing tasks to investigate differential performance, to outline a pattern o f development, and to find developmentally sensitive tasks that reflect changes in the accuracy and efficiency o f speech processing skills as children get older. It incorporates the use, where possible, o f the same, or phonetically matched, stimuli to allow valid comparison between performances on different tasks.

3.3.: Predictions

One aim o f this experiment is to find developmentally sensitive measures o f speech processing. It is expected that:

i) performance on all tasks would improve with age.

Research findings suggest that there may be differences in performance across different task paradigms. The psycholinguistic framework approach would also predict differences in performance arising from the different levels o f speech processing implicated in the task paradigms. It is, therefore, hypothesised that:

ii) performance across a range o f auditory discrimination tasks would differ.

iii) performance across a range o f speech production tasks would differ. There may be cognitive skills or generic speech processing skills that are common to both input and output speech processing task performance. It is, therefore, predicted that:

iv) performance on speech production and auditory discrimination tasks would be correlated.

However, there may also be distinctive factors that affect input and output processing differentially. It is predicted that:

v) factor analysis o f task performance will show that speech production tasks load together and auditory discrimination tasks load together.

3.4 METHOD

3.4.i Experimental Design

This experiment investigated the performance o f groups o f young children on a range o f speech processing tasks. The between - subjects variable was age, and performance was compared for children within 5 different age-groups. Within subject variables were scores for each o f 6 different experimental tasks o f speech production or auditory discrimination.

3.4.Ü Participants

One hundred 3 to 7 year-old children attending mainstream nurseries and primary schools were selected. Criteria for inclusion were:

i) no history o f speech and language difficulties or o f significant hearing loss

ii)considered by their teacher to be within the average range, with no evidence o f any general or specific learning difficulty

iii)English as a first language

iv)no significant medical or neurological condition.

v)The Edinburgh Articulation Test (Anthony et al., 1971) was administered to all participants. All participants aged between 3 and 6 years (the age-limit o f standardised data) obtained a standard score o f above 85, putting their

speech development within normal limits. The tester is a qualified speech and language therapist and during the course o f the experimental procedure screened for evidence of speech difficulties in the older children. This led to 2 potential participants being excluded from the study.

10 boys and 10 girls were included in each o f 5 age bands, 3 years, 4 years, 5 years, 6 years and Tyears (see Table 3.1). Children from at least 2 different schools were equally represented within each age-group.

Table 3.1: Subject characteristics o f participants in Experiment 1

Age Group N Mean (s.d.) Age

in years / months Range in years/months 3 year-olds 20 3;7 (0.26) 3;l-3 11 4 year-olds 20 4;5 (0.27) 4; 1-4 11 5 year-olds 20 5;6 (0.27) 5;l-5 11 6 year-olds 20 6;6 (0.29) 6;l-6 11 7 year-olds 20 7;5 (0.27) 7 ;l-7 11

The same / different task and the ABX task were only presented to the children aged 5 years and above, as a small pilot study had determined that most 3 and 4 year-old children were unable to understand how to perform the tasks reliably.

3.4.iii Task Materials and Procedures

Experimental Stimuli

Most o f the experimental tasks used stimuli based on 60 core words. A list o f 20 words were 1 syllable in length, a further 20 words were 2 syllables length, and 20 words were 3 or 4 syllables long.

Criteria for selecting stimuli words were:

i) expected to be within the vocabulary o f 3 year-old children ii) able to be illustrated pictorially

iii) word length as defined above

iv) within lists at each word length, a range o f consonants and clusters were represented

v) within the 2 and 3 or 4 syllable word-lists, half the items were able to be manipulated to make metathetic changes, when sounds are transposed within the word, e.g. ‘caterpillar’ becomes ‘capertillar’.

The stimuli were manipulated to make phonetically matched non-words for some tasks (see Table 3.2). Complete lists o f experimental stimuli are included in Appendices 1 to 4.

Table 3.2: Examples of stimuli, at each word length, for experimental tasks.

Task 1 syllable 2 syllable 3-4 syllable

Naming /Word repetition

brush

sandwich

caterpillar

NWR

/bjiJ/

/'simwod^/

Auditory discrimination

/bjAs/

/'fæmwid^/

foil)