What is that little voice inside my head? Inner speech phenomenology, its role in cognitive performance, and its relation to self-monitoring

doi:10.1016/j.bbr.2013.12.034

Behavioural Brain Research

Volume 261, 15 March 2014, Pages 220-239

https://doi.org/10.1016/j.bbr.2013.12.034 Get rights and content

Highlights

•
Behavioural, physiological and cerebral correlates of covert and overt speech.
•
Inner speech during reading and writing.
•
Inner signing and voice-hallucinations in deaf people.
•
Inner speech, mind wandering and cognitive performance.
•
Agency during inner speech.

Abstract

The little voice inside our head, or inner speech, is a common everyday experience. It plays a central role in human consciousness at the interplay of language and thought. An impressive host of research works has been carried out on inner speech these last fifty years. Here we first describe the phenomenology of inner speech by examining five issues: common behavioural and cerebral correlates with overt speech, different types of inner speech (wilful verbal thought generation and verbal mind wandering), presence of inner speech in reading and in writing, inner signing and voice-hallucinations in deaf people. Secondly, we review the role of inner speech in cognitive performance (i.e. enhancement vs. perturbation). Finally, we consider agency in inner speech and how our inner voice is known to be self-generated and not produced by someone else.

Introduction

We all hear a voice inside our brain, commonly called “inner voice”, “inner speech” or referred to as “verbal thoughts”. Inner speech is directed by oneself to oneself, and is produced in one's mind. Inner (silent) rehearsal plays a central role in the temporary storage of information in short-term memory (phonological loop). Silently verbalizing is also crucial in thinking and self-awareness. It helps in planning, problem-solving, self-motivating, reading, writing, calculating and autobiographical memory. Inner speech can thus have a positive influence on many cognitive tasks. But it can be disrupted and have a negative role. Excessive negative self-reflecting or mental rumination can interfere with cognitive performance and has been shown to be a risk factor for depression and anxiety disorders. It is also suggested that inner speech monitoring deficit may result in auditory verbal hallucinations (AVH), where one's own verbal thoughts come to be perceived as external voices. Before we examine several questions related to the phenomenology of inner speech, its role in cognitive performance and its relation to self-monitoring, we will first define inner speech, based on several descriptions from the literature.

Section snippets

Definition of inner speech

Inner speech, silent-, imagined-, covert-speech, verbal thought, are some of the terms used to refer to the silent production of words in one's mind, or the activity of talking to oneself in silence [1]. It has also been defined as the silent expression of conscious thought to oneself in a coherent linguistic form [2]. Inner speech plays a central role in human consciousness at the interplay of language and thought [3], [4]. It is a pervasive and significant human mental activity. It is

Phenomenology of inner speech

The nature of inner speech, its characteristics and manifestations have been the focus on many research studies. First, the relationship between inner and overt speech is still debated. Are the behavioural, physiological and cerebral correlates of inner speech similar to those of overt speech? Precisely, does inner speech involve articulatory representations and are the cerebral networks involved in overt speech also recruited in inner speech? Can inner speech be conceived of as an action or is

The influence of inner speech on cognitive performance

The role of inner speech in parallel attentional tasks raises substantial questions. Why do we engage in inner speech? What is the advantage of inner speech in our everyday life? Can we better explain why deliberate inner speech helps us in task-switching or problem-solving? And does excessive self-reflecting prevent us from doing some cognitive tasks?

Agency during inner speech

Another crucial question deals with agency in inner speech. How do we know that the inner voice that we hear is self-generated and not produced by another person? We process our inner speech auditorily, our inner voice has a timbre and a pitch (we can hear whether it is a question or a statement) and we can even detect errors in our own inner speech. We can imagine someone else speaking and we then hear his/her voice. So how do we not confuse these inner voices with external voices? What makes

Conclusion

An impressive host of findings on inner speech has emerged these last fifty years. Table 2 summarizes main findings and questions still to be solved. The current state of the art suggests that although many behavioural similarities exist between inner and overt speech many differences are also manifest. Neurally, overt speech is not just inner speech with added motor processes. Greater auditory cortex activation is associated with the perception of one's own overt speech, whereas inner speech

Acknowledgements

This work was supported by MLA ANR and by the LABEX CORTEX (ANR-11-LABX-0042) of Université de Lyon, within the programme “Investissements d’Avenir” (ANR-11-IDEX-0007).

References (190)

A. Morin
C.L. Heavey et al.
The phenomena of inner experience
Consciousness and Cognition
(2008)
C.L. Marvel et al.
From storage to manipulation: how the neural correlates of verbal working memory reflect varying demands on inner speech
Brain and Language
(2012)
A. Morin et al.
Self-awareness and the left inferior frontal gyrus: inner speech use during self-related processing
Brain Research Bulletin
(2007)
A. Morin
Self-awareness deficits following loss of inner speech: Dr Jill Bolte Taylor's case study
Consciousness and Cognition
(2009)
C.I. Petkov et al.
Does the brain ‘hear’ both speech and voices?
Current Biology
(2013)
D.N. Levine et al.
Language in the absence of inner speech
Neuropsychologia
(1982)
P.E. Jones
From ‘external speech’ to ‘inner speech’ in Vygotsky: a critical appraisal and fresh perspectives
Language & Communication
(2009)
L.F. Agnati et al.
Possible genetic and epigenetic links between human inner speech, schizophrenia and altruism
Brain Research Bulletin
(2012)
G.M. Oppenheim et al.
Inner speech slips exhibit lexical bias, but not the phonemic similarity effect
Cognition
(2008)

C. Fernyhough

Alien voices and inner dialogue: towards a developmental account of auditory verbal hallucinations

New Ideas in Psychology

(2004)

P. Indefrey et al.

The spatial and temporal signatures of word production components

Cognition

(2004)

C.J. Price

A review and synthesis of the first 20 years of PET and fMRI studies of heard speech, spoken language and reading

Neuroimage

(2012)

S. Basho et al.

Effects of generation mode in fMRI adaptations of semantic fluency: paced production and overt speech

Neuropsychologia

(2007)

E.D. Palmer et al.

An event-related fMRI study of overt and covert word stem completion

Neuroimage

(2001)

S. Partovi et al.

Effects of covert and overt paradigms in clinical language fMRI

Academic Radiology

(2012)

L.I. Shuster et al.

An fMRI investigation of covertly and overtly produced mono- and multisyllabic words

Brain and Language

(2005)

M. Frings et al.

Cerebellar involvement in verb generation: an fMRI study

Neuroscience Letters

(2006)

W.J. Owen et al.

FMRI of two measures of phonological processing in visual word recognition: ecological validity matters

Brain and Language

(2004)

H.J. Rosen et al.

Comparison of brain activation during word retrieval done silently and aloud using fMRI

Brain and Cognition

(2000)

A. Kielar et al.

Neural correlates of covert and overt production of tense and agreement morphology: evidence from fMRI

Journal of Neurolinguistics

(2011)

A. Moriai-Izawa et al.

Multichannel fNIRS assessment of overt and covert confrontation naming

Brain and Language

(2012)

M. Sato et al.

Multistable representation of speech forms: a functional MRI study of verbal transformations

Neuroimage

(2004)

R.C. Marshall et al.

Self-monitoring behavior in a case of severe auditory agnosia with aphasia

Brain and Language

(1985)

L. Vercueil et al.

Ictal inner speech jargon

Epilepsy & Behavior

(2013)

L. Rapin et al.

Hyperintensity of functional networks involving voice-selective cortical regions during silent thought in schizophrenia

Psychiatry Research: Neuroimaging

(2012)

J. Duncan et al.

Common regions of the human frontal lobe recruited by diverse cognitive demands

Trends in Neurosciences

(2000)

M.E. Raichle

Two views of brain function

Trends in Cognitive Sciences

(2010)

W. Hasenkamp et al.

Mind wandering and attention during focused meditation: a fine-grained temporal analysis of fluctuating cognitive states

Neuroimage

(2012)

J.W. Schooler et al.

Meta-awareness, perceptual decoupling and the wandering mind

Trends in Cognitive Sciences

(2011)

C.A. Kurby et al.

Those voices in your head: activation of auditory images during reading

Cognition

(2009)

B. Yao et al.

Brain ‘talks over’ boring quotes: top-down activation of voice-selective areas while listening to monotonous direct speech quotations

Neuroimage

(2012)

H. Lœvenbruck et al.

The left inferior frontal gyrus under focus: an fMRI study of the production of deixis via syntactic extraction and prosodic focus

Journal of Neurolinguistics

(2005)

R.A. Zwaan

The immersed experiencer: toward an embodied theory of language comprehension

Psychology of Learning and Motivation

(2003)

J.-P. Lachaux et al.

High-frequency neural activity and human cognition: past, present and possible future of intracranial EEG research

Progress in Neurobiology

(2012)

U. Bellugi et al.

Remembering in signs

Cognition

(1975)

G. Zivin

The development of self-regulation through private speech

(1979)

L.S. Vygotsky

Thought and language

(1962)

A. Morin

Possible links between self-awareness and inner speech theoretical background, underlying mechanisms, and empirical evidence

Journal of Consciousness Studies

(2005)

B. Uttl et al.

Sampling inner speech using text messaging

A.D. Baddeley et al.

Working memory

(1974)

A.N. Sokolov et al.

Inner speech and thought

(1972)

M. Perrone-Bertolotti et al.

How silent is silent reading? Intracerebral evidence for top-down activation of temporal voice areas during reading

Journal of Neuroscience

(2012)

R. Conrad

The chronology of the development of covert speech in children

Developmental Psychology

(1971)

L. Kohlberg et al.

Private speech: four studies and a review of theories

Child Development

(1968)

N. Mani et al.

In the infant's mind's ear evidence for implicit naming in 18-month-olds

Psychological Science

(2010)

C. Ngon et al.

A deep look into the developing lexicon: revelations from covert picture-naming

S.J. Gould et al.

Exaptation – a missing term in the science of form

Paleobiology

(1982)

J.B. Watson

Psychology as the behaviorist views it

Psychological Review

(1913)

J.B. Watson

Psychology from the standpoint of a behaviorist

(1919)

Cited by (196)

Distinct neural mechanisms support inner speaking and inner hearing
2023, Cortex
Humans have the ability to mentally examine speech. This covert form of speech production is often accompanied by sensory (e.g., auditory) percepts. However, the cognitive and neural mechanisms that generate these percepts are still debated. According to a prominent proposal, inner speech has at least two distinct phenomenological components: inner speaking and inner hearing. We used transcranial magnetic stimulation to test whether these two phenomenologically distinct processes are supported by distinct neural mechanisms. We hypothesised that inner speaking relies more strongly on an online motor-to-sensory simulation that constructs a multisensory experience, whereas inner hearing relies more strongly on a memory-retrieval process, where the multisensory experience is reconstructed from stored motor-to-sensory associations. Accordingly, we predicted that the speech motor system will be involved more strongly during inner speaking than inner hearing. This would be revealed by modulations of TMS evoked responses at muscle level following stimulation of the lip primary motor cortex. Overall, data collected from 31 participants corroborated this prediction, showing that inner speaking increases the excitability of the primary motor cortex more than inner hearing. Moreover, this effect was more pronounced during the inner production of a syllable that strongly recruits the lips (vs. a syllable that recruits the lips to a lesser extent). These results are compatible with models assuming that the primary motor cortex is involved during inner speech and contribute to clarify the neural implementation of the fundamental ability of silently speaking in one's mind.
Bridging phenomenology and neural mechanisms of inner speech: ALE meta-analysis on egocentricity and spontaneity in a dual-mechanistic framework
2023, NeuroImage
The neural mechanisms of inner speech remain unclear despite its importance in a variety of cognitive processes and its implication in aberrant perceptions such as auditory verbal hallucinations. Previous research has proposed a corollary discharge model in which inner speech is a truncated form of overt speech, relying on speech production-related regions (e.g. left inferior frontal gyrus). This model does not fully capture the diverse phenomenology of inner speech and recent research suggesting alternative perception-related mechanisms of generation. Therefore, we present and test a framework in which inner speech can be generated by two separate mechanisms, depending on its phenomenological qualities: a corollary discharge mechanism relying on speech production regions and a perceptual simulation mechanism within speech perceptual regions. The results of the activation likelihood estimation meta-analysis examining inner speech studies support the idea that varieties of inner speech recruit different neural mechanisms.
The domain-separation language network dynamics in resting state support its flexible functional segregation and integration during language and speech processing
2023, NeuroImage
Modern linguistic theories and network science propose that language and speech processing are organized into hierarchical, segregated large-scale subnetworks, with a core of dorsal (phonological) stream and ventral (semantic) stream. The two streams are asymmetrically recruited in receptive and expressive language or speech tasks, which showed flexible functional segregation and integration. We hypothesized that the functional segregation of the two streams was supported by the underlying network segregation. A dynamic conditional correlation approach was employed to construct framewise time-varying language networks and k-means clustering was employed to investigate the temporal-reoccurring patterns. We found that the framewise language network dynamics in resting state were robustly clustered into four states, which dynamically reconfigured following a domain-separation manner. Spatially, the hub distributions of the first three states highly resembled the neurobiology of speech perception and lexical-phonological processing, speech production, and semantic processing, respectively. The fourth state was characterized by the weakest functional connectivity and was regarded as a baseline state. Temporally, the first three states appeared exclusively in limited time bins (∼15%), and most of the time (> 55%), state 4 was dominant. Machine learning-based dFC-linguistics prediction analyses showed that dFCs of the four states significantly predicted individual linguistic performance. These findings suggest a domain-separation manner of language network dynamics in resting state, which forms a dynamic “meta-network” framework to support flexible functional segregation and integration during language and speech processing.
The nested hierarchy of overt, mouthed, and imagined speech activity evident in intracranial recordings
2023, NeuroImage
Recent studies have demonstrated that it is possible to decode and synthesize various aspects of acoustic speech directly from intracranial measurements of electrophysiological brain activity. In order to continue progressing toward the development of a practical speech neuroprosthesis for the individuals with speech impairments, better understanding and modeling of imagined speech processes are required. The present study uses intracranial brain recordings from participants that performed a speaking task with trials consisting of overt, mouthed, and imagined speech modes, representing various degrees of decreasing behavioral output. Speech activity detection models are constructed using spatial, spectral, and temporal brain activity features, and the features and model performances are characterized and compared across the three degrees of behavioral output. The results indicate the existence of a hierarchy in which the relevant channels for the lower behavioral output modes form nested subsets of the relevant channels from the higher behavioral output modes. This provides important insights for the elusive goal of developing more effective imagined speech decoding models with respect to the better-established overt speech decoding counterparts.
Shared and task-specific phase coding characteristics of gamma- and theta-bands in speech perception and covert speech
2023, Speech Communication
Covert speech is the mental imagery of speaking. This task has gained increasing attention to understand the nature of thought and produce decoding methods for brain–computer interfaces. Building on previous work, we sought to delineate and compare further the potential roles of $θ$ and $γ$ oscillations in covert speech and speech perception. Using 64-channel EEG recordings of two words and rest and employing measures of phase alignment, we found significant differential engagement of $θ$ oscillations and shared phase alignment profiles for the $γ$ -band across tasks. Our findings appear to suggest that the $θ$ and $γ$ oscillations subserve, respectively, distinct and shared encoding processes between the two tasks. Our findings can contribute to the evolving discussion regarding the similarities between output and input-based speech representations and suggests that a transferable model between the two tasks may be feasible which can lead to the development of more user-friendly covert speech brain–computer interfaces.
The emotional component of inner speech: A pilot exploratory fMRI study
2023, Brain and Cognition
Inner speech is one of the most important human cognitive processes. Nevertheless, until now, many aspects of inner speech, particularly the emotional characteristics of inner speech, remain poorly understood. The main objectives of our study are to identify the neural substrate for the emotional (prosodic) dimension of inner speech and brain structures that control the suppression of expression in inner speech. To achieve these goals, a pilot exploratory fMRI study was carried out on 33 people. The subjects listened to pre-recorded phrases or individual words pronounced with different emotional connotations, after which they were internally spoken with the same emotion or with suppression of expression (neutral). The results show that there is an emotional component in inner speech, which is encoded by similar structures as in spoken speech. The unique role of the caudate nuclei in the suppression of expression in the inner speech was also shown.

View all citing articles on Scopus

View full text

ReviewWhat is that little voice inside my head? Inner speech phenomenology, its role in cognitive performance, and its relation to self-monitoring

Highlights

Abstract

Introduction

Section snippets

Definition of inner speech

Phenomenology of inner speech

The influence of inner speech on cognitive performance

Agency during inner speech

Conclusion

Acknowledgements

Consciousness and Cognition

Brain and Language

Brain Research Bulletin

Consciousness and Cognition

Current Biology

Neuropsychologia

Language & Communication

Brain Research Bulletin

Cognition

New Ideas in Psychology

Cognition

Neuroimage

Neuropsychologia

Neuroimage

Academic Radiology

Brain and Language

Neuroscience Letters

Brain and Language

Brain and Cognition

Journal of Neurolinguistics

Brain and Language

Neuroimage

Brain and Language

Epilepsy & Behavior

Psychiatry Research: Neuroimaging

Trends in Neurosciences

Trends in Cognitive Sciences

Neuroimage

Trends in Cognitive Sciences

Cognition

Neuroimage

Journal of Neurolinguistics

Psychology of Learning and Motivation

Progress in Neurobiology

Cognition

The development of self-regulation through private speech

Thought and language

Possible links between self-awareness and inner speech theoretical background, underlying mechanisms, and empirical evidence

Journal of Consciousness Studies

Sampling inner speech using text messaging

Working memory

Inner speech and thought

How silent is silent reading? Intracerebral evidence for top-down activation of temporal voice areas during reading

Journal of Neuroscience

The chronology of the development of covert speech in children

Developmental Psychology

Private speech: four studies and a review of theories

Child Development

In the infant's mind's ear evidence for implicit naming in 18-month-olds

Psychological Science

A deep look into the developing lexicon: revelations from covert picture-naming

Exaptation – a missing term in the science of form

Paleobiology

Psychology as the behaviorist views it

Psychological Review

Psychology from the standpoint of a behaviorist

Review
What is that little voice inside my head? Inner speech phenomenology, its role in cognitive performance, and its relation to self-monitoring