Abstract

Development of executive function has received a considerable amount of attention in the literature and is known to predict a range of social, cognitive, and emotional outcomes in both children and adults. However, little is known about factors that contribute to its development in the Zambian context due to the fragmented literature available in Zambia. A literature review was conducted using five electronic databases (University of Zambia Institutional repository, Google Scholar, PubMed, BioMed Central, and EBSCO Host) to identify factors that affect executive functions in preschool and primary school children in Zambia. This review established that early childhood education, socio-economic status, physical health, and culture as factors that fall under three categories, namely research, environmental, and biological, affect the development of executive functions among children in Zambia. This review suggests that teachers, caregivers, and early childhood stakeholders in Zambia need to pay attention to both environmental and biological factors when designing executive function interventions for preschool children. A focus on improving early childhood education, nutrition, access to good quality health care, and intensifying appropriate cognitive-stimulating parenting and teaching practices that boost EF in public preschools and primary schools is required.

1. Introduction

Early childhood research in the last three decades has focused on activities and skills that prepare young children for school ^{1, 2}. Although most of these studies have targeted children in Western countries, little is known about the factors that influence executive functions (EF) and how EF affects children's performance in low-and middle-income countries ³.

Executive functions, described as key higher-order mental processes, are important for cognitive development, literacy acquisition, and school readiness ⁴. Zambia has made strides towards the attainment of one of the components of sustainable development goal number four, which is aimed at achieving equal access to early child development, care and pre-primary education for school readiness ⁵. Some of Zambia’s success stories include research efforts targeting early childhood education ^{6, 7, 8}, the establishment of a directorate for early childhood education in the Ministry of General Education, employment of early childhood education teachers ⁹, integration of early childhood centres into existing public primary schools ¹⁰ and the increased enrollment of grade one learners, especially in rural areas ⁹. Despite all these efforts, there are limited or no efforts to identify factors that influence the development of executive functions in preschool children, making it difficult to develop specific executive function interventions

Childhood executive functions have long been a popular subject in the literature. Goldman-Rakic ¹¹ investigated how object permanence is related to the development of the prefrontal cortex, a specific area of the brain responsible for executive function subcomponents such as working memory, inhibitory control, and cognitive flexibility ^{11, 12}. Diamond ¹³ confirmed the development of inhibitory control and working memory in infants. The concept of executive functions (EF) has dominated the literature but is also difficult to define given the complexity of these cognitive processes ¹⁴.

What is clear from most of the EF definitions is that these processes are not a single skill, but a set of skills that are both environmentally and biologically determined ¹⁵. It has also been observed to undergo age-related declines in older adults ^{16, 17, 18}. EF is described as a family of cognitive skills that are responsible for intentional coordination of goal-directed thought and action that tap into functional attention, inhibition, planning ¹⁹, shifting, and working memory ^{20, 21}. Executive function skills help in coordination and goal-directed behaviour ^{22, 23}. Because executive functions are so complicated, there needs to be a thorough evaluation process that is both valid and reliable in order to come to firm conclusions about what they are. Even though there have been recent changes to early childhood education ^{13, 23, 24, 25}, not much has been done in Zambia to help preschoolers improve their executive functions. It is unclear why most of the executive function studies in Zambia are limited to investigating only the cognitive components of executive functions even when there is adequate consensus among researchers that executive functions involve emotional and social behavioural processes ²³.

This paper will provide a brief overview of the importance of executive functions, their development, and the factors that influence executive functions in children. Finally, a critical analysis of the six reviewed Zambian studies will be provided. A great deal of prior research ^{21, 26, 27, 72, 73} has investigated different aspects of executive functions, including executive functions in relation to mobile technology ⁷³; health behaviour ²¹; cerebral palsy ²⁶; culture ²⁷ and socio-economic status ²⁸. However, limited studies have focused on the Zambian preschool population ⁷, and there are also quite a few studies on cost-effective EF interventions for low-income contexts. Existing research on executive functions is mainly based on older western populations rather than younger African populations. The other drawback relates to the cross-sectional nature of many prior executive function studies. Such research designs do not allow for long-term examination of executive functions ²⁷.

Promotion of executive functions in young children is important in the Zambian context because executive functions predict income and the ability to sustain employment. The high unemployment situation in Zambia and human resource conflicts locally experienced can be addressed by executive function interventions. Because executive functions contribute to job success, the risk of executive dysfunction negatively affects the household income, consequently hindering the family’s affordability to meet the basic needs of children, resulting in undernutrition, which adversely affects the physical, socio-emotional, and cognitive development of children. These negative outcomes of poverty hinder early school enrollment ⁷, negatively impacting the child’s acquisition of skills that are relevant for their survival and progression in school. If not addressed, the affected children end up performing poorly in school and getting frustrated as a result. This is likely to put children at risk of dropping out of school and engaging in criminal activities, thus creating a burden on the country's rehabilitation, correctional, and legal systems ²⁹.

The following accounts for the reasons for this review: First, there is a dearth of literature on early childhood executive functions in Zambia, which coincides with the Ministry of General Education’s recent integration of early childhood education into the public education system ¹⁰. This review was aimed at examining literature that is available on this topic to inform early childhood education practise in the public education sector. Second, the current review is aimed at demonstrating how childhood executive function research has evolved in Zambia at various grade levels. Third, to alleviate the poor reading skills, the Zambian Ministry of General Education introduced the use of Zambian local languages as a medium of instruction to enable these languages to facilitate effective linguistic and literacy development, which supports cognitive functions like executive functions. Because of this, the present review presents evidence that supports the use of executive functions as a platform for the acquisition of reading and math skills in early childhood. This study is specifically important because it might improve our understanding of some of the underlying mechanisms behind the decreased academic skills often reported in Zambian preschool schoolchildren ^{6, 30}. Fourth, this review is required in Zambia to respond to the high number of children with HIV infection ³¹. What is perhaps most distressing are the findings that some Zambian children with HIV also have executive function deficits arising from HIV infection ^{31, 32}, which necessitates further investigations into the impact of HIV on executive functions ¹². Lastly, this review is an attempt to bring together the only large-scale studies conducted in Zambia that provide interventions for effective stimulation of childhood executive functions, which have been found to not only bring about academic success but also psychological adjustment across the lifespan ³³. This review also provides an opportunity to improve our understanding of how executive dysfunction can be addressed ^{34, 35}.

One set of skills that needs to be mastered by children is executive functions, given their influence on learning, development, and future adulthood activities ^{36, 37}. A considerable number of studies have demonstrated a significant association between executive functions and key academic skills such as mathematical and reading ability ^{38, 39}.

Executive function (EF) skills are essential for not only supporting academic achievement but also promoting wellbeing across the human lifespan ^{40, 74, 75}. It is important to note that few prior systematic literature reviews have been conducted in Zambia. The following are some of the literature reviews that have been done. Cardoso and colleagues ⁷² systematically examined nineteen (19) studies that evaluated the effectiveness of executive functions interventions among typical preschool and primary school children and reported that, while the transfer of intervention gains remains inconclusive, most of the executive functions interventions used computerised school curriculum approaches and only targeted working memory relative to other executive functions components. An apparent limitation of the meta-analytic review by Cardoso and colleagues is their exclusive focus on studies undertaken in the western context. Another western-based review conducted on 45 studies by Wilmer and colleagues ⁷³ found that the impact of mobile technology habits on executive functions demonstrated that mobile technology use has adverse effects on executive functions such as attention, memory, and delayed gratification. In an investigation of the validity of executive function assessment measures in children with cerebral palsy by Pereira and others ²⁶, it was found that despite the diverse number of instruments available to assess executive functions among children, the D-KEFS was commonly used by the majority of EF studies. Another detailed systematic review on the relationship between executive function and healthy behaviour by Gray-Burrows et al. ²¹ revealed that there is a small but significant relationship between EF and health-promoting behaviour. This one is also based on studies conducted in the western context. Since the above studies only used samples from the West, it is hard to say how true their results are in Zambia.

What is known from the literature is that while executive functions are influenced both by environmental and biological factors, the role of environmental factors has dominated the literature ^{22, 41, 42}. For instance, a study of 216 preschool children from the United States of America and China aged approximately 4 years old found that, concerning general EF, Chinese children outperformed their US counterparts during the preschool period. However, there were no socioeconomic status cross-cultural differences in the observed groups ²⁷. Liu, Zhu, Ziegler, and Shi ⁴³ say that future research should look at the role of culture in the development of executive functions in preschool children in Zambia.

As earlier stated, biological determinants of executive functions have not been sufficiently investigated, especially in the Zambian preschool context. The biological bases of the following executive functions have been studied elsewhere. For example, Li, Subrahmanyam, Bai, Xie, & Liu ¹² argued that the use of modern neuroimaging technology (functional nearinfrared spectroscopy) in the study of how executive functions are influenced by physical development should be prioritised because EF is influenced by brain development ^{44, 45, 46}. The current study reviewed literature on the relationship between executive functions and physical posture.

The overall goal of this review is to examine factors that influence executive functions in young children in Zambia. Given the few executive functions studies in Zambia, the current review is important to identify the gaps that exist in prior research in this field. This review addressed the following three objectives: First, to examine factors that influence the development of executive functions in Zambian preschool children. Second, to critically examine the methods used in these studies. Finally, to assess the theoretical framework utilised in the studies that were reviewed.

2. Methods

This section examines the characteristics of the methods used in the studies selected for this review, and a description of the eligibility criteria and search strategies that were employed to obtain the relevant literature will be provided. The eligibility criteria will be explained. The following PRISMA guidelines ⁴⁷ were used to search for and select studies for inclusion in this review. All studies were categorised in terms of whether they adopted an experimental, descriptive, or mixed methods research design. The number of research participants and instruments used for data collection were also examined.

Only studies that were published between July 2001 and September 2019 among Zambian preschool and primary school children aged between 5 and 11 years old, with both male and female participants, were selected for inclusion in this review. Only publications that were available in English qualified for inclusion in this review.

Five electronic databases, including the University of Zambia Institutional repository, Google Scholar, PubMed, BioMed Central, and EBSCO Host, were searched for publications between the period from 2001 to 2019.

Computerized Boolean logic was used to search for the relevant articles in each database. Boolean logic uses three terms—and, or, and not. The present review was confined to studies that focused on different factors that influence executive functions in Zambian preschool and primary children. The following key terms were used to search for the relevant articles: ("biological factors" OR "environmental factors" OR "psychosocial factors" OR "executive function predictors") AND ("executive functions" OR "executive functions" OR "cognitive flexibility" OR "inhibitory control" OR "self-regulation" OR " behavioural regulation" OR "update" OR "planning" OR "shifting" OR "attention" OR " processing speed" OR "frontal lobe functions" OR "children" OR "child" OR "childhood" OR "preschool" OR "elementary" OR "primary" The NOT option was used as an exclusive operation to search for Zambian publications only. So, the search string was "Executive Functions AND Preschool AND Primary School AND Zambia, NOT foreign countries (United States, United Kingdom, Canada, Russia, China, Japan, and India).

3. Results

Six studies (N = 6) were included in this review. Age, gender, and educational level were analysed as follows. The participants' age ranged between 2 months and 17 years and included both males and females with no less than 5 years of education. Sample sizes ranged from 45 to 2,711 participants. Six studies (N = 6) were included because they all looked at the executive functions of children in Zambia who were in preschool or first grade.

Specifically, the studies under review were aimed at identifying factors that affect executive functions in pre and primary school children, in terms of the nature of executive functions tests used, executive function domains studied, and research design used.

Inhibitory control was the most widely assessed component of executive functions (N = 4). Most of the studies (N = 5) utilised cross-sectional research designs, while one used a longitudinal design and another one employed a cross-cultural design. All the studies utilised different statistical analyses, which included T-test, MANOVA, bivariate analysis, regression, structural equation modelling, and mixed model multi-level analysis. All these statistical tests were in line with the research questions that were addressed in the specific studies.

In terms of the factors that influence executive functions in pre and primary school children in Zambia, the studies that were reviewed identified the following seven factors: physical stature ⁴⁸, HIV status (Mwanza-Kabaghe, et al., ⁴⁹) (in press), cognitive stimulation ⁴⁸, participation in early childhood education programmes ⁷, age ³⁰, gender ⁵⁰, and culture ⁵¹.

This review critically analysed six studies according to their objectives and outcomes as follows: Study 7 (Mwanza-Kabaghe et al., in press) ⁴⁹ examined the effect of HIV infection on executive functions and found that executive functions were adversely affected by HIV infection. Study 6 ⁵¹ investigated the influence of education, culture, and language on neuropsychological test performance and found that all the neuropsychological tests were neither sensitive to the participants’ culture and education level nor sensitive to the participant's language. Study 5 ⁵² examined whether executive functions predicted literacy and numeracy skills. This study found that literacy and numeracy were associated with better working memory and inhibitory control. Study 4 ⁴⁸ explored the effect of physical posture on executive function skills and school enrollment and found that physical posture predicted not only executive functions but also on-time school enrollment. Study 3 ³⁰ assessed the problem-solving and fine motor skills of 5-year-old children and found that children from South Africa outperformed their Zambian peers on the cognitive tasks that were assessed. Study 2 ⁵⁰ investigated the relationship between teacher-reported executive functions and children’s numeracy, gender, and age. This study established that whereas numeracy was not related to executive functions, age and gender showed small positive associations. Finally, study 1 ⁷ explored the effect of early childhood education (ECE) programmes on executive functions. This study found that ECE programmes significantly improved executive function skills among preschool-aged learners.

The assessment tools used in the reviewed studies utilized neuropsychological tests for the assessment of executive functions. There was a limited range of tools used. For instance, for the measurement of attention and executive functions, the following eight tests drawn from the developmental neuropsychological assessment battery ⁵³ were administered: the tower, auditory attention, auditory response set, visual attention and design fluency tests (study 6), locally adapted pencil tapping test originally peg tapping test (study 1,4 and 5), the behaviour rating inventory of executive function (BRIEF) preschool version (study 2 and 5), Stroop-like task (study 5) and the ages and stages questionnaire version 3 (study 3). Study 7 also used the Flanker test to assess executive functions.

4. Discussion

The present review is one of the first attempts to bring together studies on executive functions in early childhood years in Zambia aimed at gaining a better understanding of how to improve key cognitive functions. The six studies that were examined in this review demonstrate the following factors that influence executive functions in children: early childhood education, socio-economic status, physical stature, and culture. Although the reviewed studies inform us of the activities that stimulate executive functions during childhood in a low-resource setting, some limitations have been noted in the theoretical framework, study design, assessment tools, and study setting. In the next section, we talk about the problems with the studies' methods and then about the different things that affect executive functioning.

While some studies (study 2 and 5) have utilised Baddeley's working memory model ⁵⁴, they have not adequately tested cognitive flexibility, an important subcomponent of executive functions. In study 5, the researcher admits leaving out cognitive flexibility because "in the current study, no hands-on cognitive flexibility tasks were used" ( ⁵²: 73). The failure to include other key components of executive functions raises questions about whether executive functions were comprehensively assessed. Inclusion of cognitive flexibility in the latest version of Baddeley’s model is a clear indication that cognitive flexibility is a critical component of executive functions ⁵⁵ relative to inhibitory control and working memory ¹⁶. The exclusion of cognitive flexibility from executive functions is a departure from the supported view of executive functions as a multidimensional concept that carries all three of the EF skills: inhibitory control, working memory, and cognitive flexibility ¹⁹.

Apart from the failure to include cognitive flexibility, the other studies (studies 1, 3, 4 and 6) in the current review have not provided information on the theoretical perspectives used, rendering the studies theoretically weak because peer-reviewed studies need to provide information about the theoretical contribution of the research undertaking. The provision of information on the theoretical framework in a study also helps to show the theoretical contribution of the study.

Regarding the executive functions (EF) assessment instruments used in the reviewed studies, most of the studies mostly used standardised EF assessment tools. For instance, the pencil tapping test, NEPSY attention and executive function subtest, Stroop test and the Behavior Rating Inventory of Executive Function (Preschool Version). The exclusive use of EF standardised tools ignores the complexity of EF as a multidimensional concept that includes both objective and subjective constructs ^{14, 56}. Future studies need to address the highlighted shortcomings so that EF measures used are as diverse as possible to respond to the multidimensional nature of EF ⁵⁶. Future studies need to utilize reliable and valid EF measures that not only examine EF in typical but also atypical children ²⁶. Other widely used, culturally sensitive EF measures for children that could be considered include the Dimensional Change Card sort task, which assesses cognitive flexibility in preschool children ⁵⁷.

Other methodological issues arising from the review include the following: First, most of the studies in the present review either used performance-based or reported measures, but none used both types of measures to holistically test EF skills. This one-dimensional approach to EF assessment is unlikely to provide a clear picture of childhood executive functions because what is assessed in a performance-based measure may not be what is captured by a reported measure. Klenberg ⁵⁶ recommends that for a full assessment of EF, both performance-based and reported measures should be administered. Future studies need to include both self-reported and performance-based measures. Second, the tendency by most western scholars to use Western-developed EF assessments in non-western contexts raises questions about the validity of the test ⁵⁸. Astatke and Serpell ⁵⁹ recommend for the development and validation of culturally appropriate EF measures. Consideration of culturally appropriate and sensitive assessment tools that address the specific socio-cultural conditions is critical for less-biased evaluation of children's cognitive skills ⁶⁰.

Lastly, the use of a single EF test to measure several EF indices can be challenging given the multidimensional nature of EF ^{61, 76}. Thus, future studies need to employ multiple assessment methods that are not only culturally sensitive but also measure all the aspects of executive functions covered in Baddeley’s executive functions model, including working memory, cognitive flexibility, and inhibitory control.

Most of the studies reviewed used cross-sectional study designs rather than randomised controlled trials, longitudinal or cross-cultural designs, making it difficult to arrive at firm conclusions regarding the developmental changes and socio-cultural factors that improve executive functions in Zambian children. EF typically follows a developmental trajectory; EF matures with brain development ( ²¹: 256). This means that research designs that investigate EF should be longitudinal to allow for monitoring of long-term EF developmental changes that occur during early childhood years, a stage in one’s life when EF grows rapidly ⁶². Cross-cultural designs help to have a better understanding of how socio-cultural mechanisms arising from culturally appropriate child rearing practices affect childhood executive functions ³⁷. While rigorous research designs are suggested, there is a need for western researchers to avoid the temptation of generalising western-based findings to non-western settings ⁶³ without paying attention to the local knowledge, attitudes, values, and beliefs ⁶⁰.

The studies selected for this review have limited sample populations that have mostly been drawn from urban areas, thus constraining our understanding of the linguistic, geographical setting, and cultural diversity of the participants being assessed. In line with this limitation, future studies should include socio-culturally diverse participants. This will allow for easy and adequate validation of standardised western-developed assessment tools for use in non-western contexts. Having noted that the study designs used in the reviewed studies were varied, this review suggests that standardisation of research designs in EF research in Zambia is needed to obtain comparable results ⁶⁴. Serpell and Nsamenang ⁶⁰ also emphasise the need to closely pay attention to rural populations due to the variations in child socialisation practises compared to urban areas.

This review was aimed at evaluating executive functions (EF) research in Zambia to better understand factors that influence early childhood executive functions among Zambian children. Early childhood education, socio-economic status, physical stature, HIV status, and socio-cultural issues have been identified to influence the development of executive functions in Zambia. The majority of the Zambian studies identified in this review have pointed to the need to target affordable EF interventions, knowing very well that Zambia is a low-resource setting. The next section discusses each of the environmental-based factors that influence executive functions among children in Zambia: early childhood education, socio-economic status, physical stature, HIV status, and culture.

As confirmed by previous studies, both study 1 and study 5 consistently found that participation in early childhood care and education programmes for 3 to 5 hours daily significantly improved executive functions in Zambian preschool children, specifically working memory and inhibitory control, predicting better performance on numeracy and literacy tasks. One of the plausible explanations for the beneficial effect of early childhood education is provided by Mckinnon & Blair ⁶⁵, who state that early education provides children with foundational skills such as language, reading, and maths that familiarise them with preliminary cognitive skills that include counting, letter identification, colour identification, counting, number recognition, and recognising the letters in one's name ⁶. With this in mind, there is a need to provide equitable access to good public quality early childhood education in Zambia ⁸. This would be one way to make up for the problems that public preschoolers have to deal with ⁶⁶.

Socio-economic factors such as caregiver income and education have been established to have strong relationships with children's performance on executive function (EF) tasks. This means that children who come from a higher socio-economic home background tend to enroll in preschools earlier than their counterparts who come from poor backgrounds. This was revealed by studies 3 and 4 in this review. These studies are consistent with other studies ²⁸ that show that working memory and inhibitory control are negatively affected by poverty. This relationship is attributed to the following reason. Poor children who are mostly stressed display limited EF skills as they enter school because their brains release cortisol, a stress hormone that disrupts optimal executive functions ⁶⁷. Poverty adversely affects optimal brain function such that neural systems that support EF development are disrupted by poverty-related risks, including under-nutrition, disease, and limited cognitive stimulation ⁴⁰. These findings have potential implications for public social policy in Zambia. First, the Zambian government needs to address challenges experienced in the social cash transfer programme and community literacy programmes. The Ministry of Education needs to make sure that all children can get early childhood education because it sets them up for future success in school and in the workplace.

As indicated by studies 4 and 7, health wellbeing as indicated by physical stature, good nutrition, and access to quality health care are strong predictors of executive functions. This is consistent with other studies ^{21, 48} that show strong links between executive functions and improved physical fitness, healthy food intake, and mindfulness ⁶⁸. The relationship between executive functions and physical development confirms the theory that the majority of children's developmental domains are interdependent ⁶⁹. This review provides support for the promotion of universal health care coverage, child and maternal health programmes in Zambia. HIV infection among children needs to be addressed by the provision of mother-to-child prevention programmes and anti-retroviral therapy.

Culture, defined as the child's behaviour norms, beliefs, values, and practices within the collectivistic arrangement, influences executive functions ²⁷. Cross-cultural differences in EF development have been noted between Chinese and American preschool children. Chinese children performed better than their American counterparts ²⁷. Previous studies support the influence of culture on executive function development ⁷⁰ Due to their early math skills ⁷⁷ and their genes ⁷⁸, Chinese children are better at executive functions. The socialisation experiences of Chinese children also play a huge role in subsequent EF development. For instance, Chinese parents effectively provide early toilet training (as early as 6 months) to their children ⁷⁸.

Given effective executive function training that is achieved through socialisation, children tend to demonstrate inhibitory control earlier than other children ⁷⁰. If collectivistic culture has a positive effect on the development of executive functions, then Zambian children, whose culture is largely collectivistic, should have adequate executive function skills. This is not the case, as revealed by some studies in this review ^{51, 52}. This could be due to the assessment tools used on Zambian children, which are not culturally appropriate, such that they are not adequately assessing executive functions. The cultural invasion of western values into Zambian society could also explain this discrepency ⁷¹. The need for the development of culturally appropriate assessment and intervention strategies is crucial.

One of the suggested measures to address the low EF skills in the Zambian population is to provide awareness to caregivers and teachers on the potential positive influences of collectivistic culture on child executive functions. Second, caregivers and teachers need to be more sensitive and responsive to the emotional, physical, and cognitive needs of children ⁷⁹. Third, Zambian children need to be trained to exercise self-control in the same manner as Chinese children are trained ⁸⁰. Lastly, teachers and caregivers need to provide opportunities for cognitive stimulation as they interact with children ^{27, 81}. If parents in Zambia did a better job of parenting and gave their children good teaching and learning tools, it could help preschool and primary school children develop their executive functions.

5. Conclusion

This literature review study was aimed at identifying methodology, environmental, and biological-based factors that affect executive function development among Zambian children. Overall, the results demonstrate that four factors contribute to the development of executive functions; these include early childhood education, socio-economic status, physical stature, and culture. These findings highlight the environmental and biological determinants of cognitive development.

The limited research base on childhood executive functions in Zambia motivated the current study, where different factors that contribute to executive functions were identified. Several implications of these findings have been earlier discussed, specifically focusing on improving early childhood education, nutrition, access to good quality health care, intensifying cognitive-stimulating parenting and teaching practices, and provision of learning materials that boost EF in public preschool and primary schools. It is important for future research in Zambia to explore the effect of parenting and teaching practices on the development of executive functions in private schools as this review exclusively examined public school studies. In addition, potential reasons for the influence of culture on executive functions need to be explored because of the pervasive influence of western cultural values on Zambian society. As one of the initial investigations to examine factors that affect the development of executive functions, this review has the potential to not only help to inform the development of strategies for preschool and primary school EF skills, but also provide information that can be useful for both teachers and parents as they think about ways to encourage cognitive development through play-based approaches.

References