Introduction. The importance of auditory feedback for learning and maintaining speech production has been frequently examined using an experimental adaptation model based on real-time formant modulation of altered auditory feedback (Houde & Jordan, 1998; Villacorta et al., 2007). When a produced vowel sound is played back with altered formants during a vowel repetition task, speakers adapt their production in the direction opposite to the imposed formant change which gradually returns to original after the removal formant perturbation as an aftereffect. Although this is consistent in normal-hearing individuals and in some disorders such as blind speakers (Trudeau-Fisette et al., 2017), Parkinson’s disease (Mollaei et al 2013) and person who stutter (Daliri et al 2018), it is still unknown whether hearing-impaired individuals using hearing devices also show adaptation to real-time formant modulation. Previous studies have shown that the cochlear-implanted individuals can adapt to other types of altered feedback such as delayed auditory feedback and frequency altered feedback (Taitelbaum-Swead et al., 2019) suggesting that such participants could also adapt to formant perturbations. We examined whether hearing-impaired participants using hearing devices show speech sensorimotor adaptation and how this is related to their speech perception ability and hearing profile. Methods. We tested fourteen normal-hearing (NH) and fourteen hearing-impaired (HI) participants using hearing-aids or cochlear implant users for a long time (>10 years). All participants were French native speakers and participated in a within-subjects procedure involving speech motor adaptation test using an altered auditory feedback and speech perception tests consisting of a speech-in noise test and vowel identification test. The HI participants were asked to fill a hearing assessment questionnaire with information regarding the onset of deafness, the hearing devices used and their duration of usage. The main sensorimotor adaptation test was carried out using altered auditory feedback. We focused on the vowel /ø/. In the test, the participants were asked to repeat /ø/ in the form of the French word ‘deux’ (/dø/) for 150 times. The second formant in the produced sound was changed over the course of the training using Audapter (Cai et al., 2008). The first 20 trials were a baseline phase with unaltered feedback. The next 50 trials were the ramp phase where the second formant was gradually increased every trial. The next 50 trials were the hold phase with a maximum formant shift, amounting to 25% relative to the participant’s second formant. The last 30 trials were an aftereffect phase where the altered feedback was removed and participants heard their own unaltered feedback. To reduce the effect of small environmental noise and bone conducted sound, small amplitude of masking noise (70 dB) was applied during the test. We evaluated the second formant, that was normalized by dividing by the mean value over the last 10 trials of the baseline phase with unaltered feedback. We quantified the adaptation amount by averaging the normalized amplitude at the end of the hold phase (average of the last 10 trials) and at the beginning of the aftereffect phase (average of the first 10 trials). Repeated-measures ANOVA was applied in each of the groups. In the speech-in-noise test, the participants identified digits presented in background noise. The signal-to-noise ratio was adjusted every trial based on their responses. The vowel identification test exploited an acoustic continuum between vowels /e/ and /ø/ including the target vowel used in the main speech motor adaptation task, the task being to categorize the presented sound as either /e/ or /ø/. We also compared how these measures concerning hearing ability and vowel identification are related to the adaptation to altered auditory feedback in HI participants. Results. In the NH participants, the hearing thresholds in the speech-in-noise test were -9.2±0.05 dB SNR. This is close to the thresholds in a previous study (-10.5±0.3 dB SNR) in French participants (Jansen et al., 2010). The HI participants showed a varied performance in both the speech-in-noise test and the vowel identification test. Based on their hearing profile, we divided the participants into two groups. The first group (HI-CI: nine participants) were long-term cochlear implant users (≥13 years) and the second group (HI-HA: five participants) were long-term hearing-aids users (> 16 years). The first group showed hearing thresholds in noise higher than the ones by NH participants (-2.5±0.9 dB SNR), but they were able to identify the vowels in the vowel identification test. In contrast, the second group showed even higher thresholds (1.1±0.9 dB SNR) and had difficulty to identify the vowels correctly. Since the adaptation task using altered auditory feedback requires a detection of small difference between the intended produced sound and actually heard sounds, HI-HA participants may not dispose of the hearing ability required for adaptation, contrary to HI-CI ones. One-way repeated measures ANOVA showed that the second formant was significantly different across these three phases in NH (F(2, 26) = 54.9, p < 0.001) and in HI-CI (F(2, 16) = 5.3, p < 0.05) but not in HI-HA (F(2, 8) = 0.3, p = 0.7). Post-hoc analyses with Tukey’s HSD showed that the second formant showed a significant decrease in the hold phase when compared with the baseline phase in NH (z = -10.1, p< 0.001) and in HI-CI (z = -3.2, p < 0.01). However, the formant was significantly different between the hold and aftereffect phase in NH (z = -2.5, p < 0.05), but not in HI-CI (z = -2.3, p = 0.07). The formant in aftereffect was also significantly different from the one in the baseline in NH (z = 7.5, p < 0.001), but not in HI-CI (z = 0.9, p = 1). Given a difference in the averaged standard deviation during the aftereffect phase between NH (0.05±0.01 (SE)) and HI-CI (0.08±0.01(SE)), the difference in aftereffect between two groups can be due to more variation in HI-CI. Individual one-sided t-tests between baseline and hold phase were carried out to verify if the adaptation was induced in individual-bases. In this test, 6 of 9 HI participants and 13 of 14 NH participants showed a significant decrease. Although the rate of 66% of participants showing an adaptation is comparable with the previous finding of adaptation (Lametti et al., 2012), this was smaller than the one in NH participants (93%) in the current data. This smaller adaptation ratio in HI participants can result in the relatively smaller amplitude of the adaptation in the averaged data. This could also be due to the unequal size of the groups (14 NH vs 9 HI-CI). Discussion. This study assessed whether HI participants using hearing devices show speech sensorimotor adaptation and whether this is dependent on factors affecting their hearing. We confirmed that our experimental setup with altered auditory feedback induces an adaption in NH participants as shown in previous studies (Trudeau-Fisette et al., 2017). Using this setup, we found that HI participants showed an adaptation only in the HI-CI group but not in the HI-HA group. The nature of auditory input from these two devices can be different because hearing-aids simply provide amplification to the sounds entering the ear in comparison to cochlear implants which bypass the damaged ear regions and directly stimulate the auditory nerve. This difference could also be seen in the result of hearing threshold in noise and vowel identification performance. In addition, while some participants in the HI-HA group have used cochlear implant for a short period, they still did not show any adaptation behavior. Altogether this suggests that HI-HA participants have a reduced ability to precisely distinguish between the minute speech sound differences compared with HI-CI ones and that a certain period of cochlear implant experience maybe required to achieve this. These findings highlight the importance of auditory feedback in controlling production mechanisms and that in HI individuals such control of speech production may be related to factors affecting their hearing.