Notes on Inner Speech

Inner Speech

Previously

  • Language is transmitted outward via speech, text, etc.
  • It is also used internally across cognitive tasks – “inner speech”

Overview of Inner Speech

  • Broad Definition: "silent" speech experience in the mind (vs. out loud); phenomenological definition.
  • Shared by many (not all); occupies ~25% waking life based on self-reported survey.
  • Interacts with cognition (memory, reading, problem-solving) and consciousness (thinking about the self). Functional role confirmed but mechanisms are not understood.
  • Dysfunction in mental disorders (rumination, auditory verbal hallucinations) remains theoretical; exact mechanisms (e.g., misattribution of inner speech) not understood.

Theories of Inner Speech

  • Speech with attenuated articulation (Watson, 1913)
    • Does not explain the self-regulatory functions of inner speech.
  • Internalised Speech by complex transformation (Vygotsky, 1934/87)
    • Emphasises roles of private/self-talk and language development.
    • Child-directed speech with caregiver creates a dialogue:
      • Example: "Look, let's cut this nail carefully,"
      • Example: "Balance, balance – look to where you are going,"
      • Example: "Yes, a nice tasty bit of yoghurt."
    • Children can use this to start self-regulating, initially saying it out loud and then internalizing.
      • Example: "Balance, balance. Well done, Joe!"
    • Evidence:
      • We tend to talk to ourselves as a dialogue rather than a monologue.
      • Explains role of speech in self-regulation.
    • Limitation:
      • Developmental theory is hard to track children from birth to their 20s to prove it!
  • Part of the phonological loop and phonological store in working memory (Baddeley and Hitch, 1974)
    • Not a theory of inner speech itself but the way in which inner speech is used the auditory (phonological) working memory system.

Methodological Considerations

  • Intrinsically difficult to study – it’s inside your head!
  • Questionnaires
    • Lack of validity and reliability
  • Experience Sampling
    • Prompted throughout day to report inner speech
    • Offline measure
  • Cognitive task
    • Phonological judgements – rhyming where you need to generate sounds
    • Not naturalistic
  • Instructed imagery
    • Give a cue and get them to imagine saying this in “your voice.”
    • Different from spontaneous inner speech.

Inner Speech ~ Speech Production: Corollary Discharge Model

  • Corollary discharge is the “prediction of the sound of one’s voice generated by the motor system.”
  • Sending a “copy” of the speech signal to other parts of the brain.
  • Normally used to filter self-caused sounds from perception.
  • Mechanism: The motor system sends out a signal to the rest of the brain (especially to the somatosensory and auditory cortex), signaling that you are about to speak, so the stimulus is probably being generated by you.
  • Articulatory planning (IFG, PMC, SMA) -> Somatosensory estimation (PO, SMG) -> Auditory representation (PO, SMG).
  • Motor – Somatosensory (converting action to perceptual signal) – Auditory cortex.
  • Since inner speech is an internal copy of your external voice, it makes sense that it may be using a similar mechanism
  • Activation of speech production regions in tasks thought to elicit inner speech:
    • Phonological Judgements
    • Rhyme judgements
    • Metrical stress judgements
    • Imagined speaking
    • Imagining saying a sentence
    • Imagining speaking in the mind
Speech Production Areas Are Engaged by Rhyme Judgements
  • Rhyme Judgements Requires phonological activation à “inner speech”
    • Example: jeans greens
  • String Matching
    • zxstkl zxstki match?
  • Rhyme Judgements > String Matching
    • Left Inferior Frontal Gyrus (L-IFG; “Broca’s”)
    • Left Premotor Cortex
Speech Production Areas Are Engaged by Imagining Talking to Oneself
  • See written word (e.g., ball) and a picture
  • Silently explain the definition of the presented word, beginning with: “This is something ….”
  • Left Inferior Frontal Gyrus (L-IFG; “Broca’s”)
  • Left Premotor Cortex
  • Supplementary Motor Area (SMA)
How to Observe/Capture Corollary Discharge?
  • Your own voice sounds different from a recording.
  • The sound you produce is attenuated by your own inner speech when you hear it back (cf. you cannot tickle yourself).
  • You notice when you make a speech error.
  • The sound you produce is checked against an internal prediction to check it is produced correctly.
  • Corollary Discharge Attenuates Auditory N100 Response
    • Auditory N1 response
    • Auditory Stimulus /BA/
    • Inner Speech /BA/
    • N1 amplitude to the spoken syllable is reduced by synchronous inner speech but not asynchronous ones à Corollary discharge cancels out the matching sound when they both take place at the same time à Corollary discharge is time-sensitive.
    • Jack et al. (2019)
Summary of Corollary Discharge Model
  • Inner speech is a pervasive mental experience implicated in a range of cognitive tasks.
  • Some inner speech is a form of ‘inner speaking’, supported by a corollary discharge mechanism.
Limitations to the Corollary Discharge Model of Inner Speech
  • Can explain inner speech in one’s own voice but not in other people’ voices.
  • Incompatible with the observation that inner speech is faster than overt speech.
  • Can explain deliberate inner speech (i.e., you intend to say something) but not spontaneous inner speech (hearing voices without explicit intention).
  • Restricts investigations to internal monologue, which is incompatible with the dialogic variety of inner speech reported.

A Perceptual Mechanism Is Needed to Support Spontaneous Inner Speech

  • Task-Elicited Inner Speech

    1. Visual prompt (to say ‘elephant’)
    2. Imagine saying the word

  • Spontaneous Inner Speech

    1. Instructed to just relax, wear a random beeper
    2. When it beeps, write down mental activity immediately on a clipboard on the lap
    3. 36 beeps in total

  • This is called Descriptive Experience Sampling

  • Spontaneous inner speech activates Heschl’s Gyrus

  • Task-elicited inner speech activates L -IFG à Not all types of inner speech rely on corollary discharge à Spontaneous inner speech is driven by activity in the auditory perceptual system

The Activation of Auditory Cortex in Silent Reading of Speech Quotes
  • Temporal Voice Areas (TVAs) à More vivid auditory representations (i.e., “inner speech”). Green areas = TVAs
  • Voice Perception Silent Reading
  • Voice Non-Voice (story scenario) followed by..
  • Eye tracking Direct Quote Indirect Quote
  • Higher activations of the right TVA when reading direct quotes
  • Yao et al. (2011)
Differential Activations Associated with Deliberate vs. Spontaneous Inner Speech
  • Deliberate:
    • Supplementary Motor Area (BA6)
    • Precentral Gyrus (BA6)
  • Spontaneous:
    • Middle Temporal Gyrus (BA22)
  • Pratts et al. (2023)

Inner Speech as Perceptual Simulation

  • ‘auditory’ representation
  • The auditory system can re-enact past auditory / speech experiences by itself.
  • What mechanisms?
Neural Oscillations – Neurons’ Firing Rhythms Capture Speech Rhythms

  • Rhythmic cycles of neuronal excitability

  • Groups of neurons in the auditory cortex firing rhythmically at different frequencies

  • Collectively generate ‘brain waves’

  • Speech Amplitude Envelope

    • Energy bursts profile in speech

  • Phase-locked

  • Overt Speech Segmentation

    • 4-7 Hz

    • 1-3 Hz

    • <1 Hz

    • 8 Hz

    • Sampled

  • Giraud & Poeppel (2012)

Spontaneous Inner Speech Driven by Oscillatory Sampling?

  • Implicit speech ‘envelope’

  • Overt Speech Segmentation

    • 4-7 Hz
    • 1-3 Hz
    • <1 Hz
    • >8 Hz

  • Neural oscillations track overt speech envelopes to segment speech signals into discrete linguistic units.

  • Synchronise Inner Speech amplitude envelope

  • “Inner speech may have an implicit envelope”

  • Neural oscillations sample linguistic thoughts in speech-like rhythms, rendering ‘thoughts’ to be experienced like ‘speech’

  • Giraud & Poeppel (2012)

  • Yao et al. (2021)

Direct Quote Reading Phase Reset
  • Brain’s rhythms are more synchronised between different direct quotes due to a more consistent reset at the beginning of a quotation
  • Higher Inter-trial Phase Synchrony
  • Aggregated across trials
  • Spontaneous Inner Speech Driven by Oscillatory Sampling?
    • Similar amount of activity in each frequency band.
    • The oscillations are aligning better in direct speech
    • This would explain why their perception is clearer.
  • Yao et al. (2021)
  • Different implicit speech rhythms The brain resets its neuronal rhythm to track the implicit speech rhythm EEG signal is transformed into energy or phase over time and frequencies.
Varieties of inner speech generation and organisation
  • If sampled in a ‘speech-like’ rhythm in the auditory system
  • Motor Command à Corollary Discharge
  • Visual Letters à Phonological Lexicon
  • Other means of verbal activation… e.g., thinking (mind-wandering)?
  • It sounds like internal speech.
  • The raw ingredients of inner speech may be generated differently.
A Dual-Mechanistic Framework to Explain Phenomenological Variety
  • Phenomenology:
    • Egocentricity
    • Spontaneity
  • Neural Mechanisms:
    • Corollary Discharge
    • Perceptual Simulation
  • Pratts et al. (2023)
Summary of Perceptual Simulation Model
  • Spontaneous inner speech in silent reading is not driven by corollary discharge.
  • Spontaneous inner speech is a form of ‘inner hearing’, arising from theta (4 -7Hz) neural oscillations that synchronise or resonate with verbal thoughts to make them sound ‘speech-like’.

How to Read Papers

  • Before you start write your self down a series of questions to try and answer them in a couple of bullet point. E.g.
    • What is the main thing they are testing?
    • How did they test it?
    • What were their main findings
    • Can I write three bullet point on the motivation/literature for their study
    • Can I find 2-3 caveats in the discussion.
  • Abstract
  • Conclusion of the introduction (and if I can’t get the key idea from hear work backwards through the intro)
  • Look at the figures to work out the key methods (depends on how good these are!) and use the methods section to aid my understanding
  • I go to the start of the discussion to understand their main findings. When I understand the main premise of the paper, if necessary I then go back to understand parts in more detail. I typically find that having a good understanding of the main premise of the study, helps me when I try to find the details or more critically assess the work.

References

  • Aparicio, M., Gounot, D., Demont, E., & Metz-Lutz, M.-N. (2007). Phonological processing in relation to reading: An fMRI study in deaf readers. NeuroImage, 35(3), 1303–1316. https://doi.org/10.1016/j.neuroimage.2006.12.046
  • Giraud, A.-L., & Poeppel, D. (2012). Cortical oscillations and speech processing: Emerging computational principles and operations. Nature Neuroscience, 15(4), 511–518. https://doi.org/10.1038/nn.3063
  • Grandchamp, R., Rapin, L., Perrone-Bertolotti, M., Pichat, C., Haldin, C., Cousin, E., Lachaux, J.-P., Dohen, M., Perrier, P., Garnier, M., Baciu, M., & Lœvenbruck, H. (2019). The ConDialInt Model: Condensation, Dialogality, and Intentionality Dimensions of Inner Speech Within a Hierarchical Predictive Control Framework. Frontiers in Psychology, 10. https://doi.org/10.3389/fpsyg.2019.02019
  • Hurlburt, R. T., Alderson-Day, B., Kühn, S., & Fernyhough, C. (2016). Exploring the ccological validity of thinking on demand: Neural correlates of elicited vs. Spontaneously occurring inner speech. PLOS ONE, 11(2), e0147932. https://doi.org/10.1371/journal.pone.0147932
  • Jack, B. N., Le Pelley, M. E., Han, N., Harris, A. W. F., Spencer, K. M., & Whitford, T. J. (2019). Inner speech is accompanied by a temporally-precise and content-specific corollary discharge. NeuroImage, 198, 170–180. https://doi.org/10.1016/j.neuroimage.2019.04.038
  • Shergill, S. S., Bullmore, E. T., Brammer, M. J., Williams, S. C. R., Murray, R. M., & McGUIRE, P. K. (2001). A functional study of auditory verbal imagery. Psychological Medicine, 31(2), 241–253. https://doi.org/10.1017/S003329170100335X
  • Yao, B., Belin, P., & Scheepers, C. (2011). Silent reading of direct versus indirect speech activates voice-selective areas in the auditory cortex. Journal of Cognitive Neuroscience, 23(10), 3146–3152. https://doi.org/10.1162/jocna00022
  • Yao, B., Taylor, J. R., Banks, B., & Kotz, S. A. (2021). Reading direct speech quotes increases theta phase-locking: Evidence for cortical tracking of inner speech? NeuroImage, 239, 118313. https://doi.org/10.1016/j.neuroimage.2021.118313
  • Pratts, J., Pobric, G., & Yao, B. (2023). Bridging phenomenology and neural mechanisms of inner speech: ALE meta-analysis on egocentricity and spontaneity in a dual-mechanistic framework. NeuroImage, 282, 120399. https://doi.org/10.1016/j.neuroimage.2023.120399