Reading and subcortical auditory function

Abstract

Although it is largely agreed that phonological processing deficits are a major cause of poor reading, the neural origins of phonological processing are not well understood. We now show, for the first time, that phonological decoding, measured with a test of single-nonword reading, is significantly correlated with the timing of subcortical auditory processing and also, to a lesser extent, with the robustness of subcortical representation of the harmonic content of speech, but not with pitch encoding. The relationships we observe between reading and subcortical processing fall along a continuum, with poor readers at one end and good readers at the other. These data suggest that reading skill may depend on the integrity of subcortical auditory mechanisms and are consistent with the idea that subcortical representation of the acoustic features of speech may play a role in normal reading as well as in the development of reading disorders. These data establish a significant link between subcortical auditory function and reading, thereby contributing to the understanding of the biological bases of reading. At a more general level, these findings are among the first to establish a direct relationship between subcortical sensory function and a specific cognitive skill (reading). We argue that this relationship between cortical and subcortical function could be shaped during development by the corticofugal pathway and that this cortical-subcortical link could contribute to the phonological processing deficits experienced by poor readers.

Figure 1.

Brain stem encoding and reading. Left to right: single nonword reading (measured with word attack) is highly correlated with brain stem timing, moderately correlated with harmonic encoding, and not significantly correlated with pitch encoding. Good readers are depicted in black symbols, intermediate readers with empty symbols, and poor readers in red symbols. Note that although outlying values were removed from the correlations presented in the text and Table 1, all data points are plotted here.

Figure 2.

Subcortical timing. Top: grand average waveforms of good (black) and poor (red) readers with major peaks (V, A, C, D, E, F, and O) labeled. Poor readers’ major peaks are significantly delayed. The stimulus is presented in gray, shifted by 8 ms to increase visual coherence with the response. Bottom: magnified peaks A, E, and O. Standard errors surrounding the mean latency of each group are denoted by the dashed lines.

Figure 3.

Brain stem encoding of harmonics (low 180–410 Hz; middle 410–755 Hz; high 755–1130 Hz). Spectra of good (black) and poor (red) readers over the 22- to 40-ms time range. Lighter, dashed lines indicate 1 standard error of the mean.