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Appendix

Cognitive Function Tests

Word generation task

Participants were asked to generate out loud as many words as they could beginning with the letter ‘S’ within 2 min, as used by Scholey et al 20011;2. This verbal fluency test was scored for the number of words that were recognizable and began with the letter ‘T’ (version 1) or letter ‘R’ (version 2) (unique with different roots).

Immediate and delayed word recall

The same list of 15 words was presented to each participant for 45 seconds. Immediately after the list was removed, and again 25 min later, participants were given two min in which to write down as many words from the list as they could remember. The list of words was adapted from Heatherley et al 2005 3using the word list generator website The words were all nouns between four and seven letters long, and they were all of similar frequency and imagery. No plurals or names were used. For both immediate and delayed recall, scores were based on the number of words recalled correctly. Items generated that were not on the list were also recorded. Two different list of words were created for the two CF versions.

Stroop colour – naming task

This selective attention task 4;5 involved naming the colour of the ink in which incongruent colour names were printed (e.g., the word ‘red’ printed in green ink). Each subject also completed a ‘control’ task, where rows of Xs the same number of letters as the name of a colour were presented in that colour. The time taken to complete both the ‘control’ and the ‘actual’ task (a total of 60 words) was recorded. Stroop task was the same for both visits.

Matrices

This task was adapted from the British Ability Scales II 6, and is thought to assess inductive reasoning (non-verbal IQ). It required participants to select a shape or arrangement of shapes that completed a sequence of similar shapes. Sixteen of these problems (matrices) were presented in order of increasing difficulty. The number of matrices completed correctly within 6 min was recorded. Two different set of patterns were created for the two CF versions.

Number search task

This speed of information and selective attention task was similar to the Sky Search task from the TEAch battery of tests 7, and a task used in a study of the effects of caffeine on children’s cognitive function and mood 3. The participants were presented with a single A4 page on which was printed a total of 1,280 single or double digit even and odd numbers. They were asked to circle blocks of three consecutive odd (version 1) or even (version 2) numbers, working from left to right and row by row as quickly and as accurately as they could. Three min were allowed to complete the task. The test was scored for the number of hits (three consecutive odd numbers correctly identified).

Serial Sevens

This working memory task was originally designed by Hayman 8, and appears to be sensitive to both lowered 9 and raised 2 blood glucose levels. The starting number, 853 (version 1) and 635 (version 2), was the same for all participants. Three minutes were given for participants to subtract the value seven, in sequence, and to say the answers out loud. It was scored for total number of correct subtractions. In case of a subtraction error, subsequent responses were scored as positive if they were correct in relation to the new number.

Mood states assessed

  1. Friendly

  1. Nervous

  1. Drowsy

  1. Happy

  1. Calm

  1. Uncertain

  1. Sad

  1. Energetic

  1. Muddled

  1. Relaxed

  1. Dissatisfied

  1. Alert

  1. Confident

  1. Tired

  1. Angry

  1. Contented

  1. Lively

  1. Tense

  1. Sluggish

  1. Clearheaded

  1. Hungry

  1. Thirsty

REFERENCES

(1) Scholey AB, Harper S, Kennedy DO. Cognitive demand and blood glucose. Physiol Behav 2001; 73(4):585-592.

(2) Kennedy DO, Scholey AB. Glucose administration, heart rate and cognitive performance: effects of increasing mental effort. Psychopharmacology (Berl) 2000; 149(1):63-71.

(3) Heatherley SV, Hayward RC, Seers HE et al. Cognitive and psychomotor performance, mood, and pressor effects of caffeine after 4, 6 and 8 h caffeine abstinence. Psychopharmacology (Berl) 2005; 178(4):461-470.

(4) Stroop JR. Factors affecting speed in serial verbal reactions. Psychological Monographs 1938; 50:38-48.

(5) Stroop JR. The basis of Ligon's theory. Am J Psychol 1935; 47:499-504.

(6) Elliot C, Smith P, McCulloch K. British Ability Scales (BAS II). Second ed. Windsor, Berkshire: 1996.

(7) Manly T, Anderson V, Nimmo-Smith I et al. The differential assessment of children's attention: the Test of Everyday Attention for Children (TEA-Ch), normative sample and ADHD performance. J Child Psychol Psychiatry 2001; 42(8):1065-1081.

(8) Hayman M. Two minute clinical tests for measurement of intellectual impairment in psychiatric disorders. Arch Neurol Psychatry 1942; 47:454-464.

(9) Taylor LA, Rachman SJ. The effects of blood sugar level changes on cognitive function, affective state, and somatic symptoms. J Behav Med 1988; 11(3):279-291.