Event-related potential asymmetries in children during pattern and phonemic processing of letters.

Event-related potentials (ERPs) were recorded at left and right anterior temporal, temporal, and parietal sites from ten children (mean age 10.45 years) during three tasks. In the detection task every letter required a response; in the form and rhyme discrimination tasks, a response was required to letters without an enclosed area or to those that did not rhyme with 'e', respectively. For all tasks, N170 peak latency was later at right temporal sites and was more negative in amplitude at right anterior temporal locations than homologous left locations. Also, left-right difference waveforms indicated that right hemisphere ERPs were more negative than the left at 200, 300 and 470 ms for most sites. These lateral differences may reflect a differential activation of the hemispheres during letter processing. Differences among the conditions were most evident for the latest positive peak at 475 ms in which detection resulted in shorter latencies and smaller amplitudes than the discrimination tasks.