Influence of family socioeconomic status on IQ, language, memory and executive functions of Brazilian children

The results show a moderate effect of SES and specifically parental education (mainly maternal education) on the performance in memory (working memory), language and executive functions, especially for younger children (from 6 to 12 years old). The children with lower SES had lower performance regarding IQ, verbal episodic and semantic memory, working memory, written language, visuoverbal memory and inhibitory control tasks than those with higher SES. The findings of the present study are consistent with those from other studies that have demonstrated the contribution of SES to cognitive performance at different age ranges, especially in younger children (Blair et al. 2011; Lupien et al. 2001; Noble et al. 2006, 2007; Piccolo et al. 2012). In fact, the magnitude of the relationship between SES and the identified factors were similar to other studies conducted in other contexts, like US and Canada (Lupien et al. 2001; Noble et al. 2006, 2007).

In the early years of childhood until school age, the socioeconomic status is a major factor since it may limit the conditions of the environment, what impacts on stimulation, access to materials and activities that favor cognitive development, presence of parents or caregivers and willingness to engage in activities with the child (Forns et al. 2012). Cognition, in general, and more specifically, memory, language and executive functions, seem to be more affected by the socioeconomic environment, due to its prolonged development – at a neuroanatomical level –, which may lead to increased susceptibility to environmental differences (Noble et al. 2006). Besides, SES is strongly related to other environmental aspects such as maternal depression and the amount of time spent by parents in activities with their children (Piccolo et al. 2012).

Our results showed that SES effects on cognition decline after nine years old. Lupien et al. (2001) found a similar result and justify that the SES differences could be due to the school environments and also to the neighborhood environments in which children are exposed as a function of SES. In this case, the neuropsychological performance would be influenced by social interactions with peers and teachers at school. In this perspective, the school system – that supposedly give the same resources for all students – and living in other spaces with another people, associated to children character (as resilience), could equalize the performance of children from different socioeconomic contexts. Another hypothesis refers to psychological characteristic of “shift-and-persist” (Chen et al. 2012), consisting of reframing appraisals of current stressors more positively (shifting), while simultaneously persisting with a focus on the future. This characteristic would be associated with reduced physiological risk in low childhood SES individuals, helping them to deal with risks environments (Chen et al. 2012).

In the present study, both the SES and specifically parental education showed independent effects, on IQ. The greatest effects were observed in younger children (up to nine years old). Studies of twins and adopted children provide evidence that genetic and environmental factors impact on general intelligence (g factor) and that a substantial part of the variation of cognitive ability in adulthood is explained by genetic variations (Blair 2006). Specifically, the heritability estimates the factor g in young children are about 20 % and decreases as a function of SES (Turkheimer et al. 2003), supposing genotypic and phenotypical contributions to cognition. A model proposed by Eaves et al. (1986) explains development as a longitudinal process that incorporates new genetic and environmental effects on the phenotype and that changes may be specific to occasions or constant over time. The continuity of cognitive performance over time and the increase in heritability with age reflect the cumulative long-term effects of a single set of genes expressed throughout development. The quality of the shared environment changes from family to family over time appears to exercise a long-term effect on cognitive development (Eaves et al. 1986).

It can be seen that SES and parental education (especially maternal education) had a moderate, but significant effect on children’s performance in written and oral language, as previously demonstrated by other studies (Noble et al. 2006, 2007). The acquisition of written language continuously improved with new skills, as the individual grows and it is totally dependent of the interactions with the environment (Finkbeiner and Coltheart 2009) that provides stimuli and experiences that are essential for this development as a primary means of social interaction (Kim 2009; Peeters et al. 2009). Low SES children are more likely to reside in an environment that exhibits sharply lower attainment levels and, in addition, that repeatedly manifests higher rates of crime, divorce, unemployment, and population density than high SES children. On the other hand, parents with high educational level tend to have substantially better educated spouses and higher family income. Also, they are more likely to invest in their children through books, providing special lessons, or availability of a computer, for example (Carneiro et al. 2013). That exposure to written material is essential for language development (Marturano 2006) and there is evidence that children whose parents read to them when they are very young are more prepared for the development of reading when they enter school due to their early contact with books (Duursma et al. 2008; Kuo et al. 2004). The lower the family SES, less frequent is the practice of literacy (Breit-Smith et al. 2010; Grieshaber et al. 2012).

Moreover, some aspects of phonological awareness, one of the best predictors of proficient reading (Foy and Mann 2003), depend on exposure to reading and home literacy (Kim 2009; Foy and Mann 2003), which also affects word recognition (Peeters et al. 2009). Mothers with higher educational level seem to be more likely to read frequently to their children than mothers with lower levels of education (Kuo et al. 2004; Skibbe et al. 2008), which may impact the development of written language in children.

It was showed that SES has an effect on memory. Dynamic models of multiple components, such as the sociocultural theory (Nelson and Fivush 2004), explains that memory development occurs through social interaction and cognitive development over the years. In the present study, children from socioeconomically disadvantaged households had poorer performance than those with high SES, especially until nine years old. According to Gathercole (1998), the basic structure of the working memory is formed at the age of six years, but the capacity of each component increases until adolescence. The main change that occurs during the development of working memory is the increase in the operational efficiency and speed of information processing, as well as greater use of strategies in problem solving, skills that are influenced by the experiences of children in the family environment (Diamond and Lee 2011; Gathercole and Baddeley 1993).

Regarding the visuospatial component of the working memory, in those cases where visuospatial processing is very complex, the central executive component is triggered to assist in solving the task (Gathercole and Baddeley 1993). In turn, these skills are influenced by the experiences of children in the family environment – opportunities to perform tasks and demands of the environment that require the use of strategies to memorize information, for example – at school, and, thus, from the SES (Nelson and Fivush 2004).

In the present study, a significant contribution of the SES and parental education (especially maternal) to the latent variable executive functions was detected. The inhibitory control (assessed by go-no go tasks for example) occurs late in childhood. At 10 years of age, the ability to inhibit attention to irrelevant stimuli and motor responses is fairly complete, being usually mastered at the age of 12 (Romine and Reynolds 2005). In agreement with this assumption, in this study, it was found that only between 10 and 12 years, the difference in the go- no go task regarding SES was significant, and low SES children performing poorer in this task compared to those from higher SES. Models that include environmental, biological and cognitive factors try to explain the development of executive functions (Blair and Ursache 2011; Stuss 1992). They integrate the results of empirical research on the physiology of stress, neurocognitive functions and self-regulation and consider the adaptive processes response to adversity of the environment as an aspect of development of the child (Blair and Raver 2012). For example, Stuss (1992) propose a model with three hierarchical levels of processing: sensory-perceptual, executive control and self-reflexivity (metacognition), that interacting with the external environment and are mediated by the frontal lobes. The levels are interrelated and depend on the maturity of primary to higher processes functioning. Also, they are related to the demands of external and internal environment, seeking to maintain the body’s adaptation in different situations. So, living in an adverse environment could impair the development of primaries levels and it would impact in the development of superior levels (Stuss 1992).

It is concluded that SES impact decreases with age, in general, except for those functions that develop at a later moment, in this case, inhibitory control. Our study measures were similar to those that have been used in other countries studies that compared SES and performance in neuropsychological tasks. Once we have achieved results similar to those found in “first world countries”, it seems that the impact of SES occurs independently of the culture studied, although the developed countries poverty rates are different from developing countries, poverty both there and here is damaging for cognitive development.

Limitations of this study include the use of a short battery that does not have many tasks to widely evaluate neuropsychological functions. Especially in the case of executive functions, few components were evaluated by the three tasks used. On the other hand, the tasks used are from an instrument made for the Brazilian child population, with standards and evidence of validity and reliability for this sample. Another limitation could be that the sample are mostly from medium or high SES and even the poorer participants do not reflect the low SES we can see in some Brazilian regions.

In sum, findings from this study indicated that outcomes in language, memory and executive functions vary by SES and that these environment effects may manifest at particular developmental stages. The study has implications for interventions, such as associating cognitive stimulation strategies to compensate for the children’s learning problems and their reduced neurocognitive development impacted by a lower SES, for example by increasing the frequency of reading and writing habits, and literacy practices, in addition to training teachers. Concerning public policies, it seems that investment in child development should start very early in life, according to this study. The investigators should consider the differences in SES in the formulation of their studies on the cognitive development. Besides, SES should be considered in the divisions of normative groups of neuropsychological tests. This study has no intention of providing a deterministic view on the effects of SES on the lives of the children and their families. Studies on this area are aimed to determine the variables that impact the development of brain and its functions and obtain tools to promote actions that revert and, ideally, prevent difficulties in children’s neurocognitive development.