Phoneme and word recognition in the auditory ventral stream

Abstract

Spoken word recognition requires complex, invariant representations. Using a meta-analytic approach incorporating more than 100 functional imaging experiments, we show that preference for complex sounds emerges in the human auditory ventral stream in a hierarchical fashion, consistent with nonhuman primate electrophysiology. Examining speech sounds, we show that activation associated with the processing of short-timescale patterns (i.e., phonemes) is consistently localized to left mid-superior temporal gyrus (STG), whereas activation associated with the integration of phonemes into temporally complex patterns (i.e., words) is consistently localized to left anterior STG. Further, we show left mid- to anterior STG is reliably implicated in the invariant representation of phonetic forms and that this area also responds preferentially to phonetic sounds, above artificial control sounds or environmental sounds. Together, this shows increasing encoding specificity and invariance along the auditory ventral stream for temporally complex speech sounds.

Fig. 1.

Foci meeting inclusion criteria for length-based CS analyses (A–C) and ALE-statistic maps for regions of significant concordance (D–F) (p < 10⁻³, k > 150 cm³). Analyses show leftward bias and an anterior progression in peak effects with phoneme-length studies showing greatest concordance in left mid-STG (A and D; n = 14), word-length studies showing greatest concordance in left anterior STG (B and E; n = 16), and phrase-length analyses showing greatest concordance in left anterior STS (C and F; n = 19). Sample size is given with respect to the number of contrasts from independent experiments contributing to an analysis.

Fig. 2.

Foci meeting liberal inclusion criteria for lexically based word-length CS analyses (A and B) and ALE-statistic maps for regions of significant concordance (C and D) (p < 10⁻³, k > 150 cm³). Similar to the CS analyses in Fig. 1, a leftward bias and an anterior progression in peak effects are shown. Pseudoword studies show greatest concordance in left mid- to anterior STG (A and C; n = 13). Notably, the distribution of concordance effects is bimodal, peaking both in mid- (−60, −26, 6) and anterior (−56, −10, 2) STG. Real-word studies show greatest concordance in left anterior STG (B and D; n = 22).

Fig. 3.

Foci meeting inclusion criteria for length-based RS analyses (A and B) and ALE-statistic maps for regions of significant concordance (C and D) (p < 10⁻³, k > 150 cm³). Analyses show left lateralization and an anterior progression in peak effects with phoneme-length studies showing greatest concordance in left mid-STG (A and C; n = 12) and word-length studies showing greatest concordance in left anterior STG (B and D; n = 16). Too few studies exist for phrase-length analyses (n = 4).

Fig. 4.

Foci meeting inclusion criteria for length-pooled analyses (A–C) and ALE-statistic maps for regions of significant concordance (D–F) (p < 10⁻³, k > 150 cm³). Analyses show leftward bias in the CS (A and D; n = 49) and AS (C and F; n = 15) analyses and left lateralization in the IR (B and E; n = 11) analysis. Foci are color coded by stimulus length: phoneme length, red; word length, green; and phrase length, blue.

Fig. 5.

Flat-map presentation of ALE cluster overlap for (A) the CS analyses shown in Fig. 1, (B) the word-length lexical status analyses shown in Fig. 2, (C) the RS analyses shown in Fig. 3, and (D) the length-pooled analyses shown in Fig. 4. For orientation, prominent landmarks are shown on the left hemisphere of A, including the circular sulcus (CirS), central sulcus (CS), STG, and STS.

Fig. P1.

Meta-analyses of auditory word processing. Matched-control sound studies (A–C), providing evidence for pattern specificity in speech processing, show a leftward bias and an anterior progression in peak effects with phoneme-length studies’ peak focus density in left mid-STG (A; n = 14), word-length studies’ peak density in left anterior STG (B; n = 16), and phrase-length studies’ peak density in left anterior STS (C; n = 19). Repetition-suppression studies (D and E) show left lateralization and an anterior progression in peak effects, with phoneme-length studies’ peak density in left mid-STG (D; n = 12) and word-length studies’ peak density in left anterior STG (E; n = 16). Peak density in studies of invariant representation (F; n = 11) and areal specialization (G; n = 15) is, respectively, left-lateralized and leftward-biased. Intensity represents activation likelihood estimation statistic value (P value for false discovery rate < 10⁻³, k > 150 cm³).