Parkinson’s disease (PD) is widely known for its impact on movement: tremor, rigidity, and slowed gait. Less visible, but equally disabling, are the changes it imposes on the voice (Duffy, 2020). Most people with PD (PwPD) develop hypokinetic dysarthria, the first symptom of which is usually reduced vocal intensity (a hallmark of hypophonia), along with a diminished pitch range and reduced articulatory precision (Duffy, 2020). These changes compromise communication quality and, consequently, social participation and quality of life (Kavya et al., 2022).

Voice production is a complex process that is both motor and non-motor, which is key to understanding the voice deficit in PwPD, who present symptoms of both types (Poewe et al., 2017). This complexity represents both a clinical and a scientific challenge. Many PwPD do not perceive changes in their own voice, such as a reduction in loudness; they may fail to notice this change, or believe their voice is adequate, even when those close to them repeat phrases such as “I can’t understand you” or “speak louder” (Silbergleit et al., 2021; Contreras-Ruston et al., 2024). This mismatch manifests in two distinct ways, how PwPD perceive their own voice in real time while speaking, and how they describe their own voice when asked about it without having spoken, or even after speaking. Both patterns reflect a deeper alteration, a failure in the sensory feedback systems that normally allow speakers to control and adjust their voice in real time (Hammer & Barlow, 2010), as well as in how that system updates information about one’s own voice after speaking, a process related to voice awareness.

Producing voice is not a unidirectional motor activity. While we speak, sensory feedback, that is, auditory and somatosensory feedback, continuously provides information that allows us to adapt our voice, for example, by adjusting its loudness or correcting pitch when we perceive that it does not sound as intended. At the same time, feedforward control relies on predictions of the sensory consequences of speech movements, allowing errors to be anticipated and corrected even before feedback arrives. This predictive control is often described in terms of an efference copy, an internal copy of the motor command, and its associated corollary discharge, the predicted sensory consequences of that command, terms increasingly preferred across neuroscience for their specificity. Together, these processes are essential for maintaining stable and intelligible speech (Tourville and Guenther, 2011; Houde and Nagarajan, 2011).

Sensory Feedback or Voice Awareness

In PD, dopaminergic dysfunction alters the basal ganglia networks that underlie sensory–motor integration (Mollaei et al., 2022; Manes et al., 2024). The result is not only a reduction in motor drive for voice production but also altered processing of sensory signals (auditory and somatosensory, as noted above) that would normally indicate that something has gone wrong, thereby allowing speech and voice to be adjusted (Hammer & Barlow, 2010). Several studies have shown that the vocal behavior of PwPD is affected when auditory feedback is experimentally manipulated. One example involves pitch-shift paradigms, in which the frequency of one’s own voice is modified in real time; in response to these perturbations, PwPD show greater difficulty adjusting vocal pitch, producing more pronounced compensations than controls (e.g., larger opposing pitch shifts in response to the same perturbation). This pattern is linked to the voice monotony characteristic of the disease and suggests dysfunction in the sensory feedback of one’s own voice (Liu et al., 2012). These deficits in sensorimotor integration affect voice control and contribute to features characteristic of PD such as reduced loudness (hypophonia) and voice monotony (Senthinathan et al., 2021).

However, real-time feedback differs from voice awareness, defined here as the retrospective, deliberate evaluation of whether one’s own voice has changed (Contreras-Ruston et al., 2024). This distinction is relevant in PD, where many PwPD do not report voice difficulties even though their voice is objectively altered (Ho et al., 2000; Liu et al., 2012). Self-report measures of voice, such as the Voice Symptom Scale (VoiSS), the Voice Handicap Index-10 (VHI-10), and the Voice-Related Quality of Life scale (V-RQOL; Deary et al., 2003; Hogikyan & Sethuraman, 1999; Rosen et al., 2004), assess general voice perception across its physical, emotional, and functional dimensions, but do not require real-time assessment. Across studies, these self-report measures show that PwPD underestimate their voice problems compared with other groups, such as people with voice disorders (e.g., behavioral or organic dysphonias) and healthy controls (Senthinathan et al., 2021; Contreras-Ruston et al., 2025).

This raises a question, given that PD mainly affects older people (Ou et al., 2021; Poewe et al., 2017; Tysnes & Storstein, 2017), is this an age-related problem? The evidence suggests otherwise; although aging alone already alters the voice (Contreras-Ruston et al., 2025; Pringsheim et al., 2014; Etter et al., 2013), the pattern observed in PD points to a mismatch specific to its underlying mechanisms. A particularly revealing finding was that the dysphonia group clearly recognized their own voice difficulties, unlike PwPD (Contreras-Ruston et al., 2024). This confirms that the lack of awareness of one’s own voice deterioration is not an effect of aging or of having an altered voice in general, but rather a feature specific to Parkinson’s disease (Contreras-Ruston et al., 2025).

Even so, self-report data fail to clarify the relationship between this lack of self-awareness and the sensory deficit underlying voice control (Hammer & Barlow, 2010); nor do they capture the day-to-day variability of voice symptoms (Janssen Daalen et al., 2025) or clarify whether the problem depends more on internal bodily signals or on external signals, such as the sound of one’s own voice (Ding et al., 2018; Waldmann et al., 2020). Therefore, these self-report data still need to be triangulated with clinical observation and experimental research.

Implications for Assessment and Treatment

These findings carry practical implications: standard self-report measures, validated for general voice disorders, fail to adequately capture the self-perception deficit specific to PD (Contreras-Ruston et al., 2024). Because PwPD systematically underreport their difficulties, relying solely on self-report may underestimate the severity of the problem, delay referral to speech-language pathology, and consequently compromise an adequate voice for communication.

Therefore, PD-specific self-report measures that do not rely on individuals’ own perceptions but also incorporate input from caregivers or clinicians are needed. Complementary indicators are also needed, such as objective acoustic measures of voice quality (e.g., cepstral peak prominence) (Delgado Hernández & Moya-Galé, 2025) and paradigms that test auditory–motor integration through real-time feedback (Contreras-Ruston et al., 2025).

This alteration of the sensory circuit could open an interesting therapeutic avenue. If PwPD do not perceive their own voice accurately, reinforcing that feedback from outside sources could help. Approaches under exploration include auditory biofeedback, real-time intensity monitoring, and intensive therapies designed for this purpose, including LSVT LOUD® (Fox & Ramig, 1997) and SPEAK OUT!® (Boutsen et al., 2018), which incorporate conscious-monitoring strategies, such as “thinking loud” or “speaking with intent,” designed to help PwPD move progressively toward more adequate voice intensity. Even so, more evidence is needed on how these therapies recalibrate feedback about one’s own voice in PD.

Looking Ahead

In PD, voice worsens more than the person manages to notice, especially in its loudness. Both self-report measures, which capture subjective awareness, and neuroimaging recordings, which capture real-time processing, point in the same direction, the difficulty in perceiving changes distorts the person’s internal sense of their own voice. In other words, if the change is not perceived, it is not adjusted; and if it is not adjusted, it never comes to be recognized as a problem.

Take-Home Messages

• Voice symptoms that go unnoticed are unlikely to be treated. In PD, awareness of one’s own voice is often missing.
• The voice deteriorates more than the person perceives, and this gap is part of the disorder. Hypophonia is not purely motor, it also involves disrupted sensory processing of one’s own voice.
• The lack of self-awareness is specific to PD, not a consequence of aging or of having an altered voice in general.
• Low self-report scores are ambiguous: they cannot distinguish a lack of awareness from compensatory strategies. Assessment should be triangulated with caregiver input, objective acoustic measures, and auditory-motor paradigms.
• Voice is also movement: its dysfunction can be as disabling as any motor failure.

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