The N400 and the fourth grade shift

Abstract

While behavioral and educational data characterize a fourth grade shift in reading development, neuroscience evidence is relatively lacking. We used the N400 component of the event-related potential waveform to investigate the development of single word processing across the upper elementary years, in comparison to adult readers. We presented third graders, fourth graders, fifth graders, and college students with a well-controlled list of real words, pseudowords, letter strings, false font strings, and animal name targets. Words and pseudowords elicited similar N400s across groups. False font strings elicited N400s similar to words and letter strings in the three groups of children, but not in college students. The pattern of findings suggests relatively adult-like semantic and phonological processing by third grade, but a long developmental time course, beyond fifth grade, for orthographic processing in this context. Thus, the amplitude of the N400 elicited by various word-like stimuli does not reflect some sort of shift or discontinuity in word processing around the fourth grade. However, the results do suggest different developmental time courses for the processes that contribute to automatic single word reading and the integrative N400.

Figure 1

A bar graph illustrating overall N400 amplitude to words (black), pseudowords (red), letter strings (dark blue), and false fonts (light blue) across the four groups (college students, fifth graders, fourth graders, and third graders). Negative is plotted up and standard error is indicated.

Figure 2

Grand average ERP waveforms elicited by words (black), pseudowords (red), letter strings (dark blue), and false fonts (light blue) for the four groups (college students, fifth graders, fourth graders, and third graders) at a single electrode site (central, medial C3). For each plot, each vertical tick along the x-axis marks 100 ms, negative is plotted up, the calibration bar (y-axis) marks 4.0 μV, and the N400 is identified.

Figure 3

Topographical voltage maps illustrating the semantic (words - pseudowords), phonological (pseudowords - letter strings), and orthographic (letter strings - false fonts) effects for the four groups. A spherical spline interpolation (Perrin et al., 1989) was used to interpolate the potential on the surface of an idealized, spherical head based on the voltages measured from the difference waves at each electrode site within the 300-550 ms time window.