Figure 1.
Schematic description of a mediation model.
In a mediation model, the effect of an independent variable X on a dependent variable Y is mediated through the mediator variable M.
Table 1.
Descriptive statistics for all variables.
Figure 2.
Schematic diagram of the TVA whole report task procedure.
Figure 3.
Performance of a typical participant for the TVA whole report task.
The mean score (mean number of correctly identified letters) is plotted against exposure time. The solid lines are the fitted curves after TVA analysis of the behavioral data for each condition.
Figure 4.
Schematic descriptions of total and mediated effects of visual processing speed on reading speed.
(Top) Schematic description of the total effect of visual processing speed on reading speed, with path c estimated from regression Equation (1). (Bottom) Schematic description of the mediated effect of visual processing speed on reading speed through VA span. Mediated effect paths a and b are respectively estimated by regression Equations (2) and (3). Path c' is estimated by Equation (3).
Table 2.
Correlation matrixfor age, VA span, TVA parameters and reading speed.
Figure 5.
Partial regression plots and sample regression model for regression VA span = age + C + K.
(Top) Partial regression plot for the effect of visual processing speed C on VA span, controlling for age. The residuals of the regression of VA span on VSTM capacity K and age are plotted against the residuals of the regression of visual processing speed C on VSTM capacity K and age. (Bottom) Partial regression plot for the effect of VSTM capacity K on VA span. The residuals of the regression of VA span on visual processing speed C and age are plotted against the residuals of the regression of VSTM capacity K on visual processing speed C and age. The solid lines represent the regression line and the shaded areas represent the regression lines' 95% confidence intervals.
Figure 6.
Regression plot and sample regression model for regression Reading Speed = VA span.
The residuals of the regression of reading speed on age are plotted against the residuals of the regression of VA span on age. The solid line represents the regression line and the shaded area represents the regression line's 95% confidence interval.
Figure 7.
Partial regression plots and sample regression model for regression Reading Speed = age + C + K.
(Top) Partial regression plot for the effect of visual processing speed C on reading speed controlling for age. The residuals of the regression of reading speed on VSTM capacity K and age are plotted against the residuals of the regression of visual processing speed C on VSTM capacity K and age. (Bottom) Partial regression plot for the effect of VSTM capacity K on reading speed. The residuals of the regression of reading speed on visual processing speed C and age are plotted against the residuals of the regression of VSTM capacity K on visual processing speed C and age. The solid lines represent the regression lines and the shaded area represent the regression lines' 95% confidence intervals.
Figure 8.
Schematic diagram of mediation analysis results.
Differences in VA span significantly mediated differences in visual processing speed. Path values are unstandardized regression coefficients with standard errors in parentheses. Significance levels are as follows: *: p<.05, **: p<.01, ***: p<.001, n.s. non-significant.