Adaptive paradigms for mapping phonological regions in individual participants

Abstract

Phonological encoding depends on left-lateralized regions in the supramarginal gyrus and the ventral precentral gyrus. Localization of these phonological regions in individual participants-including individuals with language impairments-is important in several research and clinical contexts. To localize these regions, we developed two paradigms that load on phonological encoding: a rhyme judgment task and a syllable counting task. Both paradigms relied on an adaptive staircase design to ensure that each individual performed each task at a similarly challenging level. The goal of this study was to assess the validity and reliability of the two paradigms, in terms of their ability to consistently produce left-lateralized activations of the supramarginal gyrus and ventral precentral gyrus in neurologically normal individuals with presumptively normal language localization. Sixteen participants were scanned with fMRI as they performed the rhyme judgment paradigm, the syllable counting paradigm, and an adaptive semantic paradigm that we have described previously. We found that the rhyme and syllable paradigms both yielded left-lateralized supramarginal and ventral precentral activations in the majority of participants. The rhyme paradigm produced more lateralized and more reliable activations, and so should be favored in future applications. In contrast, the semantic paradigm did not reveal supramarginal or precentral activations in most participants, suggesting that the recruitment of these regions is indeed driven by phonological encoding, not language processing in general. In sum, the adaptive rhyme judgment paradigm was effective in localizing left-lateralized phonological encoding regions in individual participants, and, in conjunction with the adaptive semantic paradigm, can be used to map individual language networks.

Figure 1

Behavioral results. Each participant is denoted with a unique color. (A) Accuracy. (B) Difficulty level of items presented. (C) Reaction time. Rhyme = Rhyme judgment; Syl = Syllable counting; Sem = Semantic matching; Perc = Perceptual control task.

Figure 2

Activation maps for group contrasts. The top row shows each language task compared to its perceptual control task: (A) Rhyme > Perceptual; (B) Syllables > Perceptual; (C) Semantic > Perceptual. The bottom row shows pairwise contrasts between the language paradigms: (D) Rhyme ≠ Semantic; (E) Syllables ≠ Semantic; (F) Rhyme ≠ Syllables.

Figure 3

Extent of activation for each paradigm in each region of interest. The gray horizontal line indicates the 2,000 mm³ extent of activation which was our threshold for considering a region activated. Each participant is denoted with a unique color, matching Fig. 1.

Figure 4

Lateralization of activation for each paradigm in each region of interest. Each participant is denoted with a unique color, matching previous figures.

Figure 5

Dice coefficients of similarity, based on split-half analyses, indicating test-retest reproducibility of each paradigm. Each participant is denoted with a unique color, matching previous figures.

Figure 6

Impact of analysis parameters on sensitivity, laterality, and reliability. Thick black outlines denote the a priori analysis parameters. Sensitivity for detection, lateralization indices, and Dice coefficients are plotted as a function of absolute and relative voxelwise thresholds (y axes), region of interest (x axes) and minimum cluster volume (x axes). Detection was defined as activation of at least 2,000 mm³ in the relevant ROI.