Use o f words and non-words in auditory discrimination tasks
Same / different and ABX auditory discrimination tasks may use word or non-word stimuli. Barton (1978, cited in Morgan 1984) found that “known vocabulary o f items to be discriminated influenced perception to a significant degree”. Significant effects o f lexical familiarity on same/ different auditory discrimination have also been found by Atchison and Canter (1979). Normally developing children between 3 and 6 years o f age were less able to discriminate non word pairs, such as ‘fa/ba’ (even after they had been trained to associate the non-words with toys and therefore to become somewhat familiar with them) than familiar word pairs, such a ‘fox/box’ (Velleman, 1988).
Differential performance between word and non-word tasks highlights possible differences arising from the influence o f the direction o f speech processing (Figures 3.1 & 3.2). In order to discriminate non-words bottom-up processing is implicated; information about the sounds contained in the stimuli must be derived from analysis o f the speech signal. On the other hand, when words familiar to the child are used, top-down
processing can occur, involving the use o f prior linguistic knowledge (i.e. semantic, phonological and orthographic). As soon as the child recognises the stimulus presented, he does not need to rely solely on his analysis o f the speech signal to do the task. Mostly speech processing involves an interaction between bottom-up and top-down processing. Some children will perform better on auditory discrimination tasks in which words are presented, but the reverse might be true in other children whose long-term phonological representations are inaccurate and interfere with their judgement.
As well as differing speech processing requirements o f the lexical and non- lexical stimuli, there may be differences in the STM demands. Bishop, Byers-Brown and Robson (1990) argue that "memory for meaningless phoneme sequences involves different processes from memory for real words" (p. 218) when lexical representations can be activated for phonological information to be retained. So, if words are used the child does not have to hold all the phonological information in a short-term store whilst he performs the comparison or judgement required, he can ‘refresh’ the stimuli by access to his existing phonological representations. This process, called ‘redintegration’ (Hulme et al., 1997), has been outlined previously in Chapter 2. For non-words, where no representations exist, this ‘refreshing’ o f the content o f the stimuli cannot take place.
Same / Different Task
For a same / different task the examiner either says the same word twice, e.g. ‘chap / chap’ or says two different words, e.g. ‘tub / tug’, (Wepman & Reynolds, 1987) and the child reports whether he has heard the same word or different words. His success with such a task will depend on his ability
to recognise and make judgements about the concepts o f same and not the same, or different. Beving and Eblen (1973) found that 4 year-old children were significantly less able to judge whether non-word pairs were the same or different than they were able to accurately repeat the non-word pairs. Beving and Eblen (1973) concluded that these young children were unable to make the relevant cognitive judgements to do the task, although they could obviously discriminate the relevant sound differences sufficiently well to achieve correct repetitions o f the non-word pairs. Task performance improved with age and 6 and 8 year-old children showed no significant difference between same/different judgements and repetition, suggesting that for older children judgement performance was a better reflection o f discrimination skill. Johnston and Hook (1978, cited in de Montford Supple, 1991) agree that such tasks are requiring “the child to compare two words and, therefore, to reflect on sounds in words and make conscious judgements about them” (p. 30). They suggest that this ‘conscious judgem ent’ may depend on a range o f other cognitive skills as much as on auditory discrimination ability.
For same / different tasks Locke (1980a) suggests there may be a mismatch between the child’s responses and the tester’s intentions. The child may discriminate “on the basis o f a cue or set o f cues the clinician does not have in mind, and may not even know about" (p. 433), for example using vowel fundamental frequency rather than voicing contrasts in /ta/ /da/ discrimination. Secondly, that the child’s “failure to respond differentially does not necessarily mean that he detects no difference between the speech stimuli" (p. 433), but that he may not consider any difference he perceives to be large enough or o f the right type to prompt a 'different' response.
(after Stackhouse & W ells, 1997) Stackhouse & Wells, 1997) (after Stackhouse & W ells, 1997) sem antic representation phonological representation I O phonetic discrim ination speech/nonspeech discrim ination recognition peripheral auditory perception sem annc representation m otor program phonological recognition phonetic discrim ination speech/nonspeech discrim ination peripheral auditory perception motor execution sem antic representation phonological representation m otor program phonological recognition phonetic discrim ination peripheral auditory perception motor execution m otor program motor execution
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=r fû U)Lower levels o f input processing skills are utilised in performing this task, from peripheral auditory processing to phonological recognition. The child may access phonological representations if the stimuli presented are words, but does not need to - as the spoken stimuli can be compared using bottom-up processing skills. A discussion o f the differences in discriminating words and non-words has already been presented earlier in this chapter, in Section 3.2.Ü. Successful performance on same/different tasks requires some STM skills as the child retains the two stimuli for long enough to make the necessary comparison and judgement (Morgan-Barrie,
1994).
A B X Task
An alternative to the same / different paradigm is an ABX presentation. The child hears 2 different stimuli (AB), usually in association with 2 puppets, one o f the stimuli is repeated (X) and the child is required to identify which puppet had spoken the repeated (X) stimuli. For example, this puppet says /b rij/ this puppet says /b n s /, who said /b rij/.
Locke (1980b) advocates this task as a useful alternative to the same / different task because it bypasses some o f the potential difficulties previously discussed in relation to same/different tasks. The same levels o f speech input processing are implicated from peripheral auditory processing to phonological recognition. I f this task uses non-word stimuli, then processing will be bottom-up, and no existing phonological representations for the stimuli will be available. There is a greater STM demand for the ABX than for the same / different task, with 3 stimuli to be compared rather than two.
Auditory Discrimination Picture Task
Locke (1980b) describes a useful procedure in which the child is presented with a picture portraying a single word that is then named either correctly or incorrectly by the examiner. For example, presenting a picture o f a ‘cat’, the examiner may say /k æ t/ or /tæ t/ and the child responds whether the
word spoken was correct or not for the given picture. This task requires the child to access his phonological representation o f the word pictured (see Figure 3.3). Correct and incorrect presentations o f the word must be compared to this stored knowledge, for the child to decide whether the word perceived matches the representation or not. All levels o f input processing are implicated. STM requirements are relatively low, as the child only has one stimulus to consider at a time. However, the child may need to hold the non-word foil in temporary storage whilst a match with an existing phonological representation is attempted.