A total of 330 children participated in this study. Their ages ranged from 7 to 14 years with a mean age of 10.83 years (SD=2.26), 196 were male (59.4%) and the most abundant subgroup came from an urban habitat (n=146, 44%), with the others coming from semi-urban (n =105, 31.8%) and rural (n =73, 22.1%) areas (six children, 2.1%, had missing values on this variable). Some of the participant’s relevant characteristics are shown in Table 1.

Table 1 Table 1 Sociodemographic characteristics of Learning Disability and Control group Notes

KBIT- Kaufman Brief Intelligence Test; IQ – Intellectual Quotient, SLI- Specific language impairment; ASD – Autism spectrum disorder, RFCT- Rey Complex Figure Test, SD – Standard Deviation.

The Learning Disability Group (LD) was composed of 190 children aged from 7 to 14 years, referred from the neuropediatric clinic of the San Cecilio Hospital in Granada (Spain) where they were being treated for LD. These children were evaluated by a clinical psychologist at the hospital’s pediatrics department to assess whether they met the conditions to be included in the study. The inclusion criteria in the LD group were the presence of continued LD that were not explained by any neuropsychological or cognitive deficit. In the LD group, a total of 120 (63.2%) children had a diagnosis of ADHD, while 53 (27.9%) had verbal LD and 17 (8.9%) had non-verbal LD.

The Control Group (CG) was composed of 140 children aged between 7 and 14 years, recruited from various schools in the province of Granada. The inclusion criteria for this group were having a proper school performance (average or over the mean grades) during several years and not having had to retake any study year. A clinical psychologist and a neuropediatrician also assessed them in order to discard any type of LD, emotional or psychiatric psychopathology.

The exclusion criteria for both groups were: (i) moderate-severe cognitive or neurological deficit assessed by Kaufman Brief Intelligence Test (2^nd Edition) and (ii) severe emotional or psychopathological alteration reported by children´s mother using the Child Behavior Checklist for ages 6-18 (Achenbach & Rescorla, 2001).

In the LD group, after application of the inclusion and exclusion criteria, an initial interview was held with the parents and the child. In this interview, the parents were informed orally and written of the purpose and content of the study, and their signed informed consent was requested. The evaluation was conducted using a set of neuropsychological tests, including those selected for this study. The order of the tests was always the same for all participants. Two neuropsychologists conducted the tests in two 90-minute sessions in a well-lit, quiet room at the San Cecilio Clinical Hospital (Granada).

The control group was composed of children with no LD, recruited from schools in the catchment area of the hospital. In this case, the same neuropsychologists as the LD group carried out the tests at the schools, using the same procedure (in two 90-minute sessions, in a quiet room, and following the same order of application). The teachers at each school informed the parents in written form, about the project, and those who agreed to participate in the study gave their informed consent.

This study was approved by the Clinical Research Ethical Committee for the province of Granada (Reference: PI-10/02735). Before participation, written informed consent was obtained from each parent or guardian. All were explicitly informed as to the voluntary nature of the study and the possibility of abandoning it at any time without having to give any explanation.

The data were analyzed using IBM-SPSS, version 21. The level of statistical significance for this study was p < 0.05. For the LD and the CG, the mean values and standard deviations were calculated for the correct and incorrect responses for each variable included in the visual memory test. To obtain normative values, four ranges of age were chosen, according to their similar neuropsychological development (see recent examples such as Burneo-Garcés et al., 2019; Mous et al., 2017): 7-8 years, 9-10 years, 11-12 years and 13-14 years. A series of ANOVAS and non-parametric comparisons for independent samples (Mann-Witney test) were conducted to determine the differences between the groups. Bivariate non-parametric correlations (Spearman’s Rho) were calculated to identify relationships between the visual memory test and other measures of visual memory and visual perception. Finally, to study the role of sociodemographic variables backward linear regression analysis were performed for each of the three dimensions of the visual memory tests, with the subject’s age, gender (0 = Boy, 1 = Girl), family habitat (which was recoded into three dummy variables: (a) 0 = rest of conditions, 1 = rural; (b), 0 = rest of conditions, 1 = semi-urban; 0 = rest of conditions, 1 = urban) and educational level of the mother (also recoded in three dummy variables: (a) 0 = rest of conditions, 1= primary, (b) 0 = rest of conditions, 1 = high school, and (c), 0 = rest of conditions, 1 = university) as independent variables. In order to increase the statistical power in the regression analysis, the entire sample was used.

Mean values for the variables of the VMT-SP, depending on the age and the group (LD and CG) are shown in Table 3. A series of ANOVAS were performed, in each of which the dependent variable was the score for the dimension of the VMT-SP and the independent variable was the group (Table 4). Statistically significant differences were found for the short-term recall, long-term recall and long-term recognition assessments. The numbers of errors in the first and third variable were also statistically different between the groups, with the children in the LD group achieving lower scores in the three main variables, recognizing fewer objects and making more errors.

A series of ANOVAs were carried out to study the influence of age on the performance of the test, using the four age groups as the independent variable. The Bonferroni correction was employed to study post-hoc comparisons. Results of the ANOVAs are shown in Table 3. For short-term recall, post-hoc analysis showed that the scores achieved by the children aged 7-8 years differed from those of the children aged 10-11 years (p = 0.001) and from those aged 12 years or older (p = 0.003). For long-term recall, there were significant differences between the children aged 7-8 years and those aged 9-10 years (p = 0.015), 10-11 years (p < 0.001) and 12 years or older (p < 0.001). The results are shown in 4 groups of age according to their cognitive development (7-8 years, 9-10 years, 11-12 years, and 13-14 years.). Finally, in long-term recognition, there were differences between the scores obtained by the children aged 7-8 years and by those aged 12 years or older (p = 0.014). In all cases, the younger children achieved worse scores in the memory tests and made more mistakes.

Table 3 Table 3 Mean values of VMT-SP on Short Term Recall, Long Recall and Recognition and its errors for all ages, 7-8, 9-10, 11-12 and 13-14 years old in control and Learning Disability group Note

SD= Standard Deviation, LD= Learning Disabilities

Table 4 Table 4 ANOVAs of VMT-SP on Short Term Recall, Long Term Recall and Recognition and its errors by Group and Age

In addition to the VMT-SP test, a previously-validated visual memory test (Rey’s complex figure) and Hooper’s test of visuospatial organisation were applied. Mann-Whitney tests were performed for independent samples, and significant differences were observed between the LD and control groups in copying the Rey figure, U = 17.764, z = 5.53, p < 0.001, d = 0.61, in recalling the Rey figure, U =16.72, z = 4.20, p < 0.001, d = 0.51, and in the total number of objects recognised in the Hooper test, U = 14.94, z = 2.85, p = 0.004, d = 0.33. In all cases, the LD group performed worse than the control group. Bivariate correlation analysis, using Spearman’s Rho was carried out of the relationship between the VMT-SP and the other tests evaluating visual aspects (Table 5), both for the LD and the control groups. Significant correlations were obtained between the scores for the three dimensions of the visual memory test and the direct scores, both in copying and in the recall of Rey’s complex figure. For the Hooper test, too, there were positive correlations with the number of objects identified in visuospatial processing.

Table 5 Table 5 Relations between the three dimensions of the VMT-SP and scores for Rey’s complex figure and for Hooper’s test for Learning Disability and Control group Note

**p < 0.01; Results for LD group (left) and the Control group (right).

Positive correlations were found between age and the scores for the three test dimensions; the older the subject, the higher the score achieved, in short term (Rho LD = 0.240, p = 0.001; Rho CG = 0.339, p < 0.001), long term (Rho LD = 0.266, p < 0.001; Rho CG = 0.396, p < 0.001), and recognition (Rho LD = 0.196, p = 0.008 ; Rho CG = 0.242, p < 0.001). Regarding gender, in the Mann-Whitney tests, the only variable presenting statistically significant differences was long-term recognition, U = 10.04, z = -2.49 p = 0.013, d = 0.27. ANOVAS were performed taking Habitat as the independent variable at three levels (urban, semi-urban and rural). The results were statistically significant for long-term, F (2.305) = 3.64, p = 0.027, partial η² = 0.023. The post-hoc analyses revealed differences between the children from rural areas and those from urban environments, with the former obtaining lower scores than those from urban areas. Finally, no significant relationships were found with respect to the level of education of the mother.

The sociodemographic variables (age, gender, habitat and mother’s level of education) were included in the backward linear regressions as independent variables (Table 6). In the first dimension, short-term recall, the final model was statistically significant, F (6, 318) = 6.27, p < 0.001, accounting for 11% of the variance (R = 0.325, R² = 0.11). The significant variables were age, and mother’s educational level (see Table 6). In the second dimension, long-term recall, the final regression model was also statistically significant, F (5, 308) = 8.44, p < 0.001, accounting for 12% of the variance (R = 0.347, R² = 0.12). In this case, the gender variable was eliminated from the model since it was not significant. Finally, with respect to long-term recognition, the final model that included age, gender and mother’s level of education (University) was statistically significant, F (5, 311) = 9.66 p < 0.001, R = 0.292, R² = 0.08).

Table 6 Table 6 Backward linear regression models, including sociodemographic variables, for each of the variables in the VMT-SP Notes

MLE= Mother’s level of education