Administración y control de inventarios

3.2.1 Participants

A full description of all children tested is presented in Chapter 2 (see Table 2.2, page 21, for group comparisons in participant characteristics). In brief, the study sample comprised 48 term-born children and 65 children born very preterm aged 8-11 years. Children born very preterm were of significantly higher age than the term-born children (term-born mean(SD) = 9.6 (1.0); very preterm mean(SD) = 10.1 (0.9);

p=0.006).

3.2.2 Procedure & Measures 3.2.2.1 Procedure

Children completed a test battery of tasks measuring basic cognitive processing and executive function, while their parent or guardian completed questionnaire measures of clinical symptoms. A full description of the procedure is presented in Chapter 2. Measures relevant to the analysis presented here are described in full below and are summarised in Table 3.1.

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Table 3.1: Summary of measures and tasks by domain.

Domain Acronym Measure or Task Score

Clinical Symptoms

Inattentive

behaviour SWAN

Strengths and Weaknesses of ADHD and Normal (SWAN) behaviour parent rating scale

Raw score from inattentive subscale

Basic Cognitive Processing

Motor processing

speed MPS

Finger-tapping subtest from the NEPSY-II Composite of time (s) for 20 repetitions on each hand Visuo-spatial processing VS-P

Arrows subtest from the

NEPSY-II Total raw score

Verbal short term

memory V-STM Immediate word recall Total number of _{items recalled in} the correct serial position

Visuo-spatial short

term memory VS-STM Immediate pathway recall Executive Function

Verbal working

memory V-WM

Word recall with concurrent face processing task in

retention interval Total number of _{items recalled in the} correct serial

position Visuo-spatial

working memory VS-WM

Pathway recall with concurrent face processing task in

retention interval Global task-

switching GS SwIFT; Switching Inhibition and Flexibility test (an adapted dimension-change shape sorting task which measures switching and interference control)

Global switch costs Local task-

switching LS Local switch costs

Interference

control IC Congruency costs

Note: ADHD = Attention-Deficit/Hyperactivity Disorder. NEPSY-II = Developmental Neuropsychology Test 2nd Edition. WASI = Wechsler Abbreviated Scale for Intelligence. SwIFT = Switching Inhibition and Flexibility test.

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Parent-rated inattention

Parent ratings from the inattentive subscale of the SWAN were used as an index of inattentive behaviour. The score was calculated as the sum of the raw score from each item of the inattentive subscale, giving a possible range of -27 to +27. Higher scores represent higher levels of inattention. Due to the computerised nature of scale completion, there were no missing items for any participant as the algorithm would not allow the parent to proceed if any items were not complete.

3.2.2.3 Measures of basic cognitive processing

Motor processing speed

Children completed the finger tapping subtest from the Developmental Neuropsychology Test (NEPSY-II; Korkman, Kirk, & Kemp, 2007) as a measure of motor processing speed. This consisted of tapping the forefinger and thumb together as quickly as possible for 20 repetitions on both the dominant and non-dominant hand. This was followed by tapping the thumb to each finger in sequence for five sequences as quickly as possible, again with both the dominant and non-dominant hand. A composite of raw scores for the repetitions trials was used in the analyses. It was calculated by summing the time taken (in seconds) for 20 repetitions on the dominant and non-dominant hand, and dividing the total by two. Higher scores represent slower processing speed. Two term-born and six very preterm children did not complete this task due to insufficient time caused by delays in the testing session.

Visuo-spatial processing

Children completed the arrows subtest from the NEPSY-II (Korkman et al., 2007) as a measure of visuo-spatial processing. On each trial the child was presented with a target surrounded by arrows on a page, and was required to indicate which arrows were pointing straight to the centre of the target. They were not allowed to trace the

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line with their fingers. The subtest was administered and scored as per the test manual.

The total raw score was used in analyses, with a maximum score of 38 arrows correctly identified, where higher scores represent better visuo-spatial processing. One term-born and five very preterm children did not complete this task due to insufficient time caused by delays in the testing session.

Verbal short term memory

Children completed a simple computer-based immediate verbal recall task programmed using PsychoPy (Peirce, 2009). They were seated at a comfortable distance from a computer screen and asked to wear a set of headphones. Volume was set to a level that was comfortable for the child. Written instructions appeared on the screen and were read out by the experimenter.

Fixation (500ms) Preparation screen (2000ms) Item 1 with auditory label (1000ms) Fixation (500ms) Item 2 with auditory label (1000ms) Response screen (Infinite)

Figure 3.1: Schematic showing an example two-span trial of the verbal short term

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Each child was required to listen to a list of words as the corresponding picture was shown on the computer screen and when cued, to try to recall the words out loud in same order that they heard them. They were explicitly told that if they realised they had forgotten a word, they could say the word ‘something’ in the place of that word so that other words were recalled in the correct position. Single-syllable words with the corresponding coloured pictures (Rossion and Pourtois, 2004) were chosen from the original Snodgrass and Vanderwart (1980) stimulus set. Pictures were chosen to present alongside the auditory representation of the item as opposed to the written word, in order to encourage a concrete representation of each item while accounting for possible differences in reading ability. All children were given the same lists of words in the same order, which was pseudo-randomised to avoid word repetitions within trials.

For each trial, a fixation cross was presented for 500ms, then the first item was presented aurally (spoken in a female voice) through the headphones, with the corresponding picture appearing on the screen for 1000ms. The 500ms fixation and 1000ms presentation of memoranda was repeated to the end of the word list for that trial. At the end of the word list, a blue question mark was presented in the centre of the screen as a recall cue for an infinite period of time, until the experimenter moved the task on. The experimenter recorded the position of each word correctly recalled on a record sheet. The experimenter then pressed the ‘spacebar’ key on the keyboard for correct trials, or the ‘x’ key for incorrect trials. Between each trial, a screen saying ‘get ready’ was presented for 2000ms. Children were not given feedback on accuracy. An example trial is shown in Figure 3.1.

The task started with only two words per span, and was programmed to allow up to eight items per span to avoid ceiling effects, increasing in one-item increments. For each child, three trials were given per span length. In order to proceed to the next span level, two of the three trials in that span level had to be recalled correctly. Only exact matches were considered correct. A trial was considered correct only when all

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words were recalled in the correct serial position. Between each span increment, a screen was presented for 2000ms to say that there would be an extra word to remember. The total number of items recalled in the correct serial position was calculated to provide a score of verbal short term memory. Three very preterm children did not complete this task due to insufficient time caused by delays in the testing session.

Visuo-spatial short term memory

Children completed a simple computer-based visuo-spatial immediate recall task programmed using PsychoPy (Peirce, 2009). They were seated a comfortable distance from the computer screen. Written instructions were presented on the screen and were read out by the experimenter, asking children to help a pirate to find his treasure. A four-by-four grid of black squares on a white background was presented. For each trial, after a delay of 500ms, gold coins appeared one-by-one for

Figure 3.2: Schematic showing an example two-span trial of the visuo-spatial short

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1000ms each in different positions across the grid.

Following this, a blue question mark was presented for 1000ms in the centre of the grid to cue the child to recall the positions of the coins (see Figure 3.2). They were asked to click on the squares (using the mouse) where the coins appeared, and to try to do it in the same order that they saw the coins appear. The software recorded the locations of mouse-clicks and, when the child had clicked in the corresponding number of locations on the grid, the task proceeded to the next trial. Between each trial, a screen was presented for 2000ms telling the child to ‘get ready’. Trials were only considered correct if all locations were recalled in the correct serial position. As with the verbal memory tasks, three trials were given per span length. In order to proceed to the next span level, two of the three trials in that span level had to be recalled correctly. The experiment started with only two locations per span, and was programmed to allow up to eight locations per span to avoid ceiling effects. Between each span increment increase a screen was presented for 2000ms to state that there would be an extra coin to remember.

No locations were repeated within a single trial. Sequences were chosen that aimed to minimise factors aside from item number that have been shown to affect trial difficulty such as the number of internal crossings (Busch, Farrell, Lisdahl-Medina, & Krikorian, 2005; Orsini, Pasquadibisceglie, Picone, & Tortora, 2001) and distance between locations (Orsini, Simonetta, & Marmorato, 2004). The total number of items recalled in the correct serial position was calculated to provide a score of visuo-spatial short term memory. Two term-born children did not complete this task due to insufficient time caused by delays in the testing session.

3.2.2.4 Measures of executive function

Verbal working memory

The task used to measure verbal working memory was identical to the verbal short term memory task described above (see Section 3.2.2.3), with the exception of a 5000ms retention interval between the list presentation and recall, during which

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children completed a concurrent processing task. Different word lists from the short term task were used to prevent practice effects but stimuli were selected in the same way. Instructions were adjusted to explain the nature of the new aspect of the task and to give examples of the concurrent processing task. Once again instructions were both presented on screen and orally by the experimenter.

In order to ensure comparable concurrent processing during both the verbal working memory task described here, and the visuo-spatial working memory task described below, the same concurrent processing task was used. A relatively domain neutral task was selected as it has been shown that recall can be negatively impacted when the concurrent processing task taps into the same domain being measured in the memory task (Shah & Miyake, 1996). The concurrent processing task chosen involved

Concurrent face task (5000ms) Response screen (Infinite) Fixation (500ms) Preparation screen (2000ms) Item 1 with auditory label (1000ms) Fixation (500ms) Item 2 with auditory label (1000ms)

Figure 3.3: Schematic showing an example two-span trial of the verbal working

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a simple ‘same or different’ judgement of two photographs of faces presented on the screen, taken from the Glasgow Face Matching Test (Burton, White, & McNeill, 2010) and presented in a random order. Previous research shows that this task is not verbal, nor does it correlate with visual short term memory (r=0.050; Burton et al., 2010)

The child was asked to judge whether the faces presented were two pictures of the same person, or pictures of two different people, and to give their response out loud to the experimenter by saying ‘same’ or ‘different’. The experimenter then pressed the ‘1’ key on the keyboard for ‘same’ and the ‘2’ key for ‘different’. If the child completed a judgement before the 5000ms retention interval was complete, they were presented with a second set of faces, and so on, to ensure that despite individual differences in processing speed, all children were required to process the task for the full 5000ms. The experimenter ensured that children did not use the interval simply to rehearse the memoranda. Following this, a blue question mark appeared in the centre of the screen to cue word recall, as in the verbal short term memory task described above.

Scoring was conducted as for the short term memory task above, with the same span levels and the same criteria for proceeding to the next span. The procedure of the recall task was not contingent on successful face judgements. An example trial can be seen in Figure 3.3. The total number of items recalled in the correct serial position was calculated to provide a score of verbal working memory with higher scores indicating better working memory. One term-born child and three very preterm children did not complete this task due to insufficient time caused by delays in the testing session.

Visuo-spatial working memory

The visuo-spatial working memory task was identical to the visuo-spatial short term memory task described above (see Section 3.2.2.3), with the exception of a 5000ms retention interval during which children completed a concurrent processing task. The concurrent processing task used was identical to the domain-neutral face-processing

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task used in the verbal working memory task, where children were asked to judge whether two photographs of faces were two photographs of the same person, or photographs of two different people. On each trial, following the presentation of the coin locations, the concurrent processing task was presented for 5000ms, before the response grid appeared on screen with the blue question mark to cue location recall. Written and oral instructions were adjusted and examples of the amended procedure were given. Scoring was conducted as for the short term memory task above with the same span levels and the same criteria for proceeding to the next span. The total number of items recalled in the correct serial position was calculated to provide a score of visuo-spatial working memory with higher scores indicating better working memory. Two term-born children and one very preterm child did not complete this task due to insufficient time caused by delays in the testing session.

Switching and interference control

Children completed a modified version of the SwIFT (Switching, Inhibition and Flexibility task; FitzGibbon, Cragg, & Carroll, 2014), a simple computerised shape and colour matching task programmed using PsychoPy (Peirce, 2009). The child was seated a comfortable distance from the screen wearing a set of headphones. The volume in the headphones was set to a comfortable level for the child. Written instructions were presented on the screen and read out by the experimenter. Throughout the task, prompt and response stimuli consisted of two different shapes (specifically designed so that they did not have verbal labels, henceforth described as shape A and shape B) and two different colours (also specifically chosen as faded colours that were difficult to verbally label; red-ish and blue-ish, henceforth referred to as red and blue for ease of description), so that four possible stimuli could be used (A-red A-blue, B-red, B-blue). On each trial, the outline of a black box was presented at the top centre of the screen for 1000ms. The prompt stimulus was then presented within the box, together with an auditory cue (a female voice saying ‘colour’ or ‘shape’). After a delay of 500ms, two response stimuli were then presented below, one on the right and one on the left of the screen. If children heard the word ‘colour’

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they were required to choose the response stimulus that matched the prompt on the basis of colour. If they heard ‘shape’, they were required to choose the response stimulus that matched the prompt on the basis of the shape. All stimuli remained on the screen until the child responded. To choose the response stimulus on the left side of the screen, children pressed the ‘z’ key on the keyboard, or for the response stimulus on the right side of the screen, the ‘m’ key. Star-shaped stickers were placed on the keys as reminders, and children were told to ‘keep their fingers on the stars’, so that they could respond as quickly as possible. An example of a full trial is shown in Figure 3.4.

The task was designed so that there were six different trial types resulting from two levels of congruency (congruent and incongruent) and three levels of switching (pure, switch mixed, and non-switch mixed). To begin with, each child completed two blocks of 12 pure trials. In each of these ‘pure’ blocks, children were required to match on the same dimension throughout the duration of the block, producing one block of 12 trials where children matched the response stimuli to the prompt only on the basis of colour, and a separate block of 12 trials where they matched only on the basis of shape. The order of these blocks was counterbalanced across participants.

Figure 3.4: Schematic for examples of congruent (left) and incongruent (right) trials

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Prior to these blocks, children completed two practice trials with visual feedback. If the child gave incorrect responses on practice trials, more practice trials were given until the child responded correctly on two consecutive trials.

Following the two ‘pure’ blocks, children completed three ‘mixed’ blocks of 24 trials, where half of the trials required them to match on colour, and the other half required them to match on shape. Trials were organised so that after the first trial in each block, subsequent trials could be labelled as either ‘switch trials’, whereby the dimension used for matching was different to the one on the previous trial (e.g. trial two: ‘shape’, trial three: ‘colour’), or ‘non-switch trials’, whereby the same dimension was used for matching as in the previous trial (e.g. trial two: ‘shape’, trial three: ‘shape’). So in total there were 24 pure trials, 34 non-switch mixed trials and 35 switch mixed trials. This allowed us to measure both global task switching, by comparing response time on mixed blocks to pure blocks, and local task switching, by comparing performance on switch trials to non-switch trials within the mixed blocks. A further 3 trials, one at the beginning of each of the 3 the mixed blocks, could not be considered to be either ‘switch’ or ‘non-switch’ as there was no preceding trial and were excluded from the analysis.

Half of all trials in each block were labelled as ‘congruent trials’. For congruent trials the correct response stimulus matched the prompt stimulus on both colour and shape dimensions, while the incorrect response stimulus did not match on either dimension (for an example of a congruent trial see Figure 3.4, left). On congruent trials the prompt matches the response stimulus on the left on both the colour and shape dimension, but does not match the response stimulus on the right on either dimension, thus regardless of the instruction, the response stimulus on the left would be the correct response option). The other half of trials were ‘incongruent