On the planum temporale lateralization in suprasegmental speech perception: evidence from a study investigating behavior, structure, and function

Abstract

This study combines functional and structural magnetic resonance imaging to test the "asymmetric sampling in time" (AST) hypothesis, which makes assertions about the symmetrical and asymmetrical representation of speech in the primary and nonprimary auditory cortex. Twenty-three volunteers participated in this parametric clustered-sparse fMRI study. The availability of slowly changing acoustic cues in spoken sentences was systematically reduced over continuous segments with varying lengths (100, 150, 200, 250 ms) by utilizing local time-reversion. As predicted by the hypothesis, functional lateralization in Heschl's gyrus could not be observed. Lateralization in the planum temporale and posterior superior temporal gyrus shifted towards the right hemisphere with decreasing suprasegmental temporal integrity. Cortical thickness of the planum temporale was automatically measured. Participants with an L > R cortical thickness performed better on the in-scanner auditory pattern-matching task. Taken together, these findings support the AST hypothesis and provide substantial novel insight into the division of labor between left and right nonprimary auditory cortex functions during comprehension of spoken utterances. In addition, the present data yield support for a structural-behavioral relationship in the nonprimary auditory cortex.

Keywords: anatomical asymmetry; asymmetric sampling in time; auditory cortex; functional lateralization; speech perception.

Figure 1

Stimulus manipulation. The top portion illustrates a detail of the waveform of an original sentence, which is multiplied by the cosine windows, and then locally time reversed. In this example, segment length is 200 ms. This procedure results in a bottom waveform. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]

Figure 2

Sequence of a single trial. Gray squares: volume acquisitions; Long waveform: sentence stimulus; Short waveform: probe stimulus; +: fixation cross; ?: response screen.

Figure 3

Percent of correct answers from the in‐scanner pattern‐matching task (±1 SE).

Figure 4

Here, the functional lateralization index (LI; ± 1 SE) in anatomically defined ROIs is displayed; positive values indicate L > R lateralization; HG, Heschl's gyrus (red); PT, planum temporale (green); pSTG, posterior superior temporal gyrus (blue). **P < 0.001.

Figure 5

Here, the percent of correct answers from the in‐scanner pattern‐matching task (±1 SE) is depicted separately for the two groups of cortical thickness lateralization in planum temporale (PT). [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]