Frontiers in Aging Neuroscience · Oct 31, 2026
Age-Group Differences in the Temporal Structure of Speech and Forehead total-Hb Responses During a Phonemic Verbal Fluency Task: A Comparison of Adults in Their 40s and 70s
By Kenji Nakamura
In populations with well-preserved cognitive function, cognitive screening total scores tend to cluster near the ceiling, making it difficult to characterize age-group differences from total scores alone. We compared the temporal structure of word production, acoustic features, and the timing of forehead total-hemoglobin (total-Hb) responses during a phonemic verbal fluency task between two specifically recruited groups: care-house staff in their 40s and care-house residents in their 70s. A total of 254 participants (115 staff in their 40s, 139 residents in their 70s) completed a 60-s phonemic verbal fluency task requiring words beginning with the Japanese syllable /ka/, administered as part of the Japanese version of the Montreal Cognitive Assessment (MoCA-J). We derived the total word count, word counts in 10-s bins, a residual-time summary per valid word, the final-production-bin endpoint, and three exploratory acoustic measures (smoothed cepstral peak prominence [CPPS], jitter, and shimmer). Time-to-peak (TTP) was computed from forehead total-Hb signals recorded with a wearable single-wavelength near-infrared spectroscopy device. MoCA-J scores clustered near the ceiling in both groups, although the group difference was significant. The 70s group produced fewer words (14.00 ± 1.18 vs 17.09 ± 1.33) and had a longer TTP (32.97 ± 9.31 vs 15.63 ± 4.98 s). In exploratory acoustic analyses of the recorded word segments, CPPS was lower in the 70s group, whereas no clear group difference in jitter was detected. Word counts across 10-s bins showed a group × time-bin interaction. Within each group, participants who produced more words showed longer TTP. The group difference in TTP remained after adjustment for the final production bin and within strata of that bin. Even when screening scores clustered at the ceiling, the temporal structure of word production and forehead total-Hb responses differed between the two recruited groups, and the measures showed different patterns of group difference. Because age group was confounded with participant role and recruitment source, and single-wavelength total-Hb signals do not index localized neural activity, the findings are descriptive and motivate longitudinal, multi-axis characterization of speech in aging.