Draft:Atypical STS Function in Autism

Atypical Superior Temporal Sulcus Function in Autism refers to structural and functional differences in the superior temporal sulcus (STS) observed in individuals with autism spectrum disorder (ASD). The STS plays a central role in speech perception, prosody, audiovisual integration, biological motion, and gaze processing. Since the early 2000s, a number of neuroimaging studies have suggested that the STS responds differently in autistic individuals during language-related and social tasks.

Overview

Findings on STS function in autism are not uniform. Some studies show reduced posterior STS activation during social perception tasks, while others show preserved or atypically timed activity during speech and prosody tasks. Because the STS sits between sensory analysis and higher-level linguistic interpretation, differences here may affect how speech and speaker intent are processed.

Attention and gaze strongly influence STS responses. For example, Pelphrey (2005) reported that autistic participants who looked less at a speaker’s face showed weaker STS activation during live-interaction speech.

Anatomy

Although anatomically a single sulcus, the STS includes several subdivisions:

• Posterior STS (pSTS) – sensitive to biological motion, gaze shifts, and audiovisual speech.
• Middle STS – involved in phonological structure, prosody, and rhythmic cues.
• Anterior STS – selective for voices and paralinguistic information.

The STS has reciprocal connections with the superior temporal gyrus (STG), the inferior frontal gyrus (IFG), and the temporoparietal junction (TPJ). In neurolinguistic models such as Hickok & Poeppel’s ventral stream, middle–posterior STS contributes to mapping speech sounds onto meaning.

Typical function

In non-autistic listeners, the STS contributes to:

• distinguishing phonological contrasts such as /ba/ vs. /da/
• tracking pitch, rhythm, and emotional prosody
• audiovisual speech integration, especially in noisy conditions
• recognizing biological motion and point-light walkers
• aspects of Theory of mind, particularly in pSTS

Studies using naturalistic spoken narratives (e.g., Lerner et al. 2011) show that superior temporal regions, including the STS, track the unfolding of connected speech over time and are sensitive to sentence- and paragraph-level structure.

Atypical function in autism

Social perception

Pelphrey et al. (2005) found that in autistic adults, posterior STS activity failed to differentiate between congruent and incongruent gaze shifts, unlike in non-autistic controls. Kaiser et al. (2010) reported weaker or more diffuse pSTS responses during point-light walker viewing. However, Hadjikhani et al. (2006) showed that when attention is tightly controlled, pSTS responses may appear closer to typical patterns.

Speech and prosody

Several neurolinguistic studies report differences in prosody and phonology processing:

• Paul et al. (2005) showed reduced middle STS activation for emotional prosody contrasts.
• Studies of syllable-rate entrainment (e.g., Giraud & Poeppel, 2012) report weaker STS synchronization to rapid speech rhythms.

Audiovisual speech

Autistic individuals often show reduced audiovisual integration in speech:

• In typical development, audiovisual emotion and speech perception benefit from combining facial and vocal cues, as shown in work by de Gelder & Vroomen (2000).
• In autistic individuals, several studies report reduced audiovisual speech integration (for example, weaker gains from seeing the talker’s face or reduced susceptibility to the McGurk effect)

This may make speech-in-noise more difficult despite normal hearing thresholds.

Connectivity

Several studies report atypical connections involving the STS:

• reduced arcuate fasciculus coherence between middle STS and IFG (Keller et al. 2007)
• weaker structural connectivity between pSTS and TPJ in children with autism (Carmody et al. 2010)

• reduced functional connectivity between anterior STS and affective voice-processing regions (Kaiser et al. 2016)

Development

Jones and Klin (2013) found reduced preference for biological motion in infants who later developed autism. Seery et al. (2013) reported atypical lateralization of ERP responses to native and non-native speech in infants at high familial risk for autism spectrum disorder over the first year of life.

Associated language features

Because STS supports phonology, prosody, and audiovisual integration, atypical responses may relate to:

• reduced sensitivity to emotional prosody
• differences in turn-taking and timing
• atypical gesture–speech integration
• difficulty interpreting sarcasm or indirect speech
• less reliable inference of speaker intention

Not all autistic individuals show these features, but several studies report correlations with STS activity.

Research methods

fMRI

Common paradigms include:

• listening to sentences with contrasting intonation
• silent videos of mouths forming syllables
• biological motion stimuli (point-light walkers)
• naturalistic movies or storytelling

Naturalistic tasks often produce larger group differences.

EEG/MEG

Used to measure:

• mismatch negativity to pitch changes
• audiovisual mismatch responses
• entrainment to speech envelope and syllable-rate oscillations

DTI & resting state

Used to evaluate white-matter tracts and long-range connectivity between STS and IFG, TPJ, or auditory cortex.

Eye-tracking is frequently combined with fMRI because gaze strongly influences STS activation.

Controversies

Interpretation remains debated. Some researchers argue that reduced STS responses reflect less attention to social cues, while others note differences even in non-social tasks such as pure prosody perception. Autism is also heterogeneous, and some individuals show typical or even heightened activation depending on the task.

Summary of STS findings in autism

STS subregion	Typical function	Atypical finding in autism	Notes
Posterior STS	Biological motion, audiovisual cues	Reduced or inconsistent activation	Strong gaze effects
Middle STS	Prosody, phonology	Delayed pitch tracking; weaker prosodic contrasts	EEG evidence strong
Anterior STS	Voice identity	Reduced voice selectivity	Seen in infants
Connectivity	Links with IFG, TPJ, fusiform gyrus	Altered structural & resting-state links	Heterogeneous findings

See also

• Superior temporal sulcus
• Autism spectrum disorder
• Biological motion
• Prosody
• Theory of mind
• Inferior frontal gyrus