i STM Task Paradigms

As suggested above the input and output mechanisms used in STM tasks may be auditory / verbal or visual / pictorial. Different combinations o f presentation and response mode can be used. It is possible to examine the

speech processing demands o f these tasks, in the same way as auditory discrimination and speech production tasks were analysed in Chapter 3. Again, this is based on the Stackhouse and Wells (1997) speech processing model.

1. SISO, Spoken Input - Spoken Output Task. Stimuli are presented in a spoken form and recall is spoken. Speech input processing, from peripheral auditory processing to phonological representation, and speech output processing, from motor programme to motor execution, is involved (see Figure 5.1).

2. SIPO, Spoken Input - Picture-pointing Output Task. Stimuli are presented in a spoken form and recall is by picture-pointing. Speech

input processing, from peripheral auditory processing to semantic representation is involved, but speech output processing is not (see Figure 5.2).

3. PISO, Picture Input - Spoken Output Task. Stimuli are presented in a pictorial form and recall is spoken. Speech input processing is not involved, but speech output processing, from semantic representation to motor execution is involved (see Figure 5.3).

The research has concentrated on the input mechanism o f spoken words or picture presentation, with less attention paid to the response mechanism. Speech processing models would predict differences in performance for pictorial and spoken presentations and responses. Although some studies have used different task paradigms with children, analysis has not always considered differences in performance o f the two types o f stimuli, in terms o f number o f items correctly recalled (Hulme, 1987, Hitch et al., 1989a).

Adams and Gathercole (2000) presented two STM tasks to 4 year-old children. In both tasks, the stimuli were presented verbally and the response was either spoken (i.e. SISO) or by pointing to pictures (i.e. SIPO). There was no significant difference in recall between the spoken response condition and the picture-pointing response condition. Visual inspection o f the data suggested that a small number o f children (4 out o f 30) produced longer spans when the response was pointing to a picture (SIPO) than when the response was spoken (SISO). Lovatt, Avons and Masterson (2000) also used a spoken presentation with different response mechanisms, with adults. However, they did find significantly greater recall for the picture pointing response (SIPO) than for the spoken response (SISO).

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A key issue is the process by which pictorial stimuli are remembered, as compared to spoken stimuli. The phonological loop component o f the WM model assumes that spoken material enters the phonological short-term store, and is maintained by the sub-vocal rehearsal process. However, for picture material it is less clear. The WM model proposes that visual inputs have access to the phonological loop, but that the material first has to be recoded in a speech-based form through the sub-vocal rehearsal process. This recoded material can then be maintained in STM in the same way as spoken material. Researchers have found differences in the way in which children recall spoken and picture material. A major focus o f research has been the stage o f development, and the age, at which the facility to recode picture material in a speech-based form, and hence, use o f the phonological loop to recall picture material, comes into play. Development o f the sub-vocal rehearsal process has been discussed in Chapter 2. Reviews o f the evidence suggest that this does not emerge until the age o f 7 or 8 years (Gathercole & Martin, 1996, Henry & Millar, 1993, Baddeley et al., 1998).

These issues have been addressed by using the variables o f phonological similarity and word-length in experimental studies to test whether the phonological loop is being utilised for picture recall. Serial recall tasks for pictures showed effects o f both phonological similarity (Hulme, 1987, Ford & Silber, 1994) word-length and concurrent speech (Hulme et al.,

1986) in children aged from 4 years to 10 years. Hitch, Halliday, Schaafstal and Schragen (1988) also found a small word length effect on recall o f pictures by 5 year-olds. These findings suggest that 4 year-old children are using speech coding, i.e. the phonological loop, as a means o f memorising pictorial material. However, not all studies have confirmed

these findings. Hitch et al. (1989a) reported that children did not show any significant effect o f word length on recall for pictures until after the age o f 8 years. There was no significant effect o f phonological similarity on picture recall for 5 year-old children (Hitch et al., 1989c, Longoni & Scalisi, 1994) or for 3 year-old children (Palmer, 2000). Six and seven year-old children did show a phonological similarity effect, suggesting use o f a speech-based code (Palmer, 2000). However, Palmer noted that there were individual differences in the age at which phonological recoding began to be used, with phonological similarity effects found in some children as young as 5 years, but absent in some children at age 8 years.

There are differences in task presentations across these studies which might account for some o f the variation in findings. In some studies the tester presented the pictures for recall silently (e.g. Hitch et al., 1989a, Hitch et al., 1989c, Longoni & Scalisi, 1994). In others the tester also named the pictures as they were presented (Hulme et al., 1986, Hulme,

1987), or requested the child to name the picture as it was presented (Hitch, et al., 1988). If the pictures were named by tester or child at presentation, then this might trigger the recoding o f picture material into a speech based form. Hulme et al. (1986) named the pictures to half o f the children in their experiment, and presented the pictures silently to the other half. There was no significant effect o f experimenter naming on recall. However, this is in contrast to the finding o f Ford and Silber (1994). They compared children’s recall o f pictures when the children named the pictures and when they were encouraged to remain silent. The children aged 3 to 5 and 5 to 11 years remembered significantly more words in the naming than in the silent condition, and this was more marked in the younger group. Palmer (2000) found that there was no significant

difference in recall for 3, 6 and 7 year-old children whether they were asked to name the pictures presented or had been asked to remain silent.

Another influential task variable is whether or not the children spontaneously name the pictures presented. In the studies by Hitch et al. (1989a), and Hitch et al. (1989c) the tester presented the pictures silently. The children were either told not to say the names o f the pictures aloud, although they could “do what you like in your head”, or to silently name the pictures “ with your lips”. Recall was spoken. There was no effect on performance o f allowing the children to silently name, however there was a significant interaction between word length and naming, suggesting that naming was more important for maintaining longer words in STM. Hulme et al. (1986) monitored the children’s subvocal speech movements, without putting any restrictions on the child naming the pictures as they tried to remember them. Four year-old children tended to overtly name the pictures they were recalling, and a proportion o f older children used sub-vocal rehearsal. It may be that this naming o f the pictorial stimuli, overtly or sub- vocally, by the children generated the stimuli in a speech-based form that could be retained in the phonological loop for recall. Hitch et al. (1989a) and Hitch et al. (1989c) were in effect preventing the young children from using the mechanisms and strategies available to them. This may be more important for younger children who tended to spontaneously overtly name the pictures in Hulme et al’s (1986) study.

A third factor that may influence whether or not the phonological loop is used to recall picture material in young children, is the response mode. It is possible that if recall is spoken, children will tend to recode the pictures in a speech based form at presentation, whereas if recall is through a picture-

pointing response they might not. However, Hitch et al. (1988, 1989a) and Longoni and Scalisi (1994) argue that before the age o f 7 years, phonological coding only occurs at the time o f spoken recall. This seems to be confirmed by Ford and Silber (1994) who used a spoken response, but only found phonological similarity effects when the children had labelled the pictures at presentation. Palmer’s (2000) study also used a spoken response, but did not find a phonological similarity effect in younger children.

The differing conditions under which experiments have been carried out may account for the differences in findings. Whether or not the tester or child names the pictures as they are presented, and if the response is spoken, rather than pictorial, affects the degree to which speech processing skills might be implicated in performance.

Picture recall has been found to be affected by visual similarity effects in younger children (Hitch et al., 1988, Longoni & Scalisi, 94). This is interpreted to suggest that visual strategies and the visuo-spatial scratchpad are implicated in picture recall. Although, again findings have been mixed. For example. Hitch et al. (1989a) found no significant effect o f visual similarity (elongated objects portrayed at the same 45’ angle) on picture recall in children aged 4 years and over.

It is clear that there may be differences in performance on STM tasks that use different modes for presentation o f stimuli and for response. These may reflect the STM mechanisms involved, such as the way in which stimuli are coded. They may also reflect the differing levels o f speech processing involved. Where direct comparisons have been made for

performance across a range o f paradigms (Adams & Gathercole, 2000, Lovatt et al, 2000) findings are inconclusive, and only 2 o f the possible 3 paradigms are used.

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