Several factors were considered in the selection o f words for use in the fixed list lengths to be presented. Word frequency measures were not considered reliable for use with young, pre-reading children as these are based on written frequency (Carroll, Davies & Richman, 1971). Spoken word frequency measures (e.g. Brown, 1984) are based on adult derived data. Age o f acquisition (AoA) measures relate to the age at which children first leam a word. These have been calculated from adult ratings o f when a word was first learned (Gilhooly & Logie, 1980, Carroll & White, 1973). AoA has been found to be a better predictor o f performance on object naming than word frequency, in adults (Brown & Watson, 1987, Morrison, Ellis & Quinlan, 1992).Walley and Metsala (1992) found children to be more likely to recognise words with earlier AoA, and that children’s ratings o f AoA o f words was the same as adults. Morrison,
Chappell and Ellis (1997) found significant correlations between rated AoA and objective AoA as measured in children. They conclude that “adult ratings provide a reliable and valid measure o f real word learning age” (p. 528).
As this study involved the testing o f young children, AoA was considered to be the most important factor in stimuli selection, and word frequency was not controlled for. Gilhooly and Logie (1980) (and Carroll & White, 1973) rate words on a scale from 1-7. Point 1 corresponds to an AoA o f 0- 2 years, point 2 to an AoA of 3-4 years, and so on.
The stimuli for the memory tasks at T l consisted o f 12 words with a phonologically simple structure and 12 words with a phonologically complex structure. Words were selected according to the following criteria:
i) Age o f acquisition by 4 years, i.e. AoA rating o f 1 or 2 (Gilhooly & Logie, 1980, Carroll & White, 1973).
ii) Noun, able to be illustrated by colour photograph.
iii) Not included in stimuli lists for experimental speech processing tasks, used in further experiments, to be reported later (see Chapter 6).
iii) Single syllable, containing only ‘pure’ vowels (i.e. not dipthongs); and either phonologically simple in structure (with no clusters present), i.e. CVC, or phonologically complex in structure (with one 2 element consonant cluster present in each word), i.e. CCVC or CYCC.
A set o f words matching these criteria were recorded from live voice, onto a Kay DSP Sonograph, Model 5500. Waveform analyses o f the speech
signal were used to time 3 live spoken durations o f each word. A mean measure o f time for spoken duration was calculated for each word. Visual inspection o f the mean durations was used to prepare a set o f 12 phonologically simple words, and a corresponding set o f 12 phonologically complex words. The words across the two lists were paired to match as closely as possible on mean spoken durations, (see Table 5.1). An independent samples t test showed no significant difference between mean spoken durations for simple and complex word lists, t(2 2> =.088
(p=.993). The mean o f the differences between shortest and the longest duration o f the live utterances o f each word was larger than the mean o f differences in timings between each complex word and its matched simple word. This suggests that any difference between a complex and a simple word was no greater than the difference that would be found in duration when saying the same word more than once. No significant difference was found in age o f acquisition ratings for the simple and complex word lists (F(i,23) =.87, p=.361).
The items from each o f the 2 stimuli lists were grouped into three sets o f 4 stimuli. The following criteria were used:
i) Absence o f phonological similarity between items, for example words with the same onsets or vowels were not placed in the same set.
ii) The total duration o f each set o f 4 items to be as close as possible.
iii) The matched pairings between words were maintained in the production o f the sets, so that set A contained 4 simple words and the 4 complex words matched on spoken duration, (see Table 5.1).
The order o f the words in each set were varied to produce 3 different word orders for the 3 STM tasks. The matched pairs occurred in the same place
in each string so that the first item in the string for simple words was o f similar duration to the first item in the string for complex words etc. (see Table 5.1).
Table 5.1: Stimuli sets for T l tasks.
Set Simple Mean duration Complex Mean duration
word in sees (s.d.) word in sees (s.d.)
A Tap .5229 (0 2 ) Clock .5276 (.03)
Bus .5010 (.01) Bread .4953 ( 01)
Sock .6364 (.03) Spoon .6620 (.05)
Leaf .6068 (.04) Crab .5547 (.02)
Total mean duration 2.2671 2.2396
B Cup .4719 (.01) Drum .4938 (0 3 )
Ring .5448 (.01) Frog .5500 (0 3 )
Shop .6203 (.02) Tent .6391 (0 4 )
Horse .6073 (0 3 ) Bridge .5521 (0 2 )
Total mean duration 2.2443 2.2350
C Girl .5016 (0 2 ) Plug .5182 (0 3 )
Pig .4406 (0 2 ) Brick .4677 (0 2 )
Fork .6604 (0 3 ) Box .6765 (0 2 )
Cheese .7291 (0 6 ) Flag .6859 (.01)
Total mean duration 2.3317 2.3483
At T2, as the children were one year older, and some had scored highly on the tasks presented at T l, additional items were generated for each word list, so that the fixed list length was 5 items. The extra stimuli were generated using the same criteria as for T l stimuli. As before, there was no
significant difference in mean spoken durations for the phonologically simple and the phonologically complex stimuli, t (2 8) = -.075, p = .941.
Stimuli were allocated to fixed lists o f 5 words in the same way as before (see Table 5.2).
Table 5.2: Stimuli sets for T2 tasks
Set Simple Mean duration Complex Mean duration
word in secs (s.d.) word in secs (s.d.)
A Cup .4719 (.01) Drum .4938 (0 3 )
Ring .5448 (.01) Fox .5344 (.02)
Cheese .7291 (0 6 ) Sweet .6927 (0 3 )
Girl .5016 (0 2 ) Plug .5182 (0 3 )
Horse .6073 (0 3 ) Bridge .5521 (0 2 )
Total mean duration 2.8547 2.7912
B Knife .5604 (0 3 ) Frog .5500 (0 3 )
Bus .5010 (.01) Bread .4953 (0 1 )
Shell .6453 (0 2 ) Box .6765 (0 2 )
Sock .6364 (0 3 ) Spoon .6620 (.05)
Leaf .6068 (0 3 ) Crab .5547 (0 2 )
Total mean duration 2.9499 2.9385
C Shop .6203 (0 2 ) Swing .6427 (0 2 )
Church .6146 (0 2 ) Tent .6391 (0 4 )
Pig .4406 (0 2 ) Brick .4677 (0 2 )
Fork .6604 (0 3 ) Flag .6859 (.01)
Tap .5229 (0 2 ) Clock .5276 (0 3 )