Table 4.
Partial parameters, paradigm and results of tES effect speech understanding studies.
| Reference | Sample Size | Stimulation Types | Stimulation Electrode Position and Size |
Reference Electrode Position and Size |
Stimulation Parameters |
The Number of Stimulation Sessions | Auditory Paradigm | TACS Time Lags | TACS Phase Relationships | Results |
|---|---|---|---|---|---|---|---|---|---|---|
| Wilsch, et al., 2018 [102] | 19 | Envelope—tACS/sham | Simultaneous Cz (35 cm2) T3 and T4 (4.18 × 4.18 cm) |
Unspecified | between 0.4 mA–1.5 mA unspecified time |
Two stimulation sessions | Oldenburg sentence test | 0–250 ms, in 50-ms steps | Unspecified | The sinusoidal fit with an average frequency of 5.12 Hz has a good effect on envelope-tACS modulation of speech intelligibility |
| Zoefel, et al., 2020 [103] | Group 1: n = 27 Group 2: n = 19 |
Group 1: unilateral tACS and sham Group 2: bilateral tACS and sham |
Group 1: T7 (3 × 3 cm) C3 (5 × 7cm). Group 2: T7 and T8 doughnut-shaped electrodes inner ring (d 1 = 2 cm, t 2 = 0.1 cm) external ring (outer d 1 = 10 cm, inner d 1 = 7.5 cm, t 2 = 0.2 cm) |
Unspecified | Group 1: 1.7 mA Group 2: 1.2 mA unspecified time |
Two stimulation sessions | Speech comprehension test (rhythmic noise-vocoded speech) | 0–280 ms, in 40-ms steps | 0–7π/4, in steps of π/4 | Modulation of speech perception induced by tACS in the case of bilateral stimulation using ring electrodes |
| Kadir, et al., 2020 [105] | 17 | Envelope—tACS/sham | Simultaneous T7 and T8 (35 cm2) |
Either side of the Cz (35 cm2) | between 0.2–1.5 mA unspecified time |
Two stimulation sessions | Speech comprehension test (SRT assessment) | Fixed lag times of 100 ms and 250 ms | 0–5π/3, in steps of π/3 | Between a short latency of 100 ms and a long latency of 250 ms, the modulation of speech understanding by the phase of the stimulus was different |
| Keshavarzi, et al., 2020 [106] | 18 | Envelope—tACS/sham | Simultaneous T7 and T8 (35 cm2) |
Either side of the Cz (35 cm2) | between 0.7 mA-1.3 mA unspecified time |
Two stimulation sessions | Speech comprehension test (SRT assessment) | Unspecified | 0–5π/3, in steps of π/3 | The tACS effect speech understanding in the θ band, had no effect on speech understanding in the δ band Compared with the sham stimulation, the current stimulation in the θ band can improve the understanding of speech in noise |
1 d, diameter; 2 t, thickness.