How Subtle Pitch Changes Affect Speech Understanding

A groundbreaking study by Northwestern University, in collaboration with the University of Pittsburgh and University of Wisconsin-Madison, has uncovered a new role for a key brain region in processing speech prosody—the subtle changes in pitch that convey meaning, emphasis, and intent in conversation. The findings, published in Nature Communications, challenge long-held assumptions about how and where the brain interprets the melody of speech.

How the Brain Interprets Speech Beyond Words?

For decades, scientists believed that prosody—the rise and fall of pitch in speech—was processed primarily in the superior temporal gyrus, a brain region associated with speech perception. However, this new study redefines speech processing, revealing that Heschl’s gyrus, previously thought to be involved in only early auditory processing, also encodes pitch accents as meaningful linguistic units.

According to Dr. Bharath Chandrasekaran, co-principal investigator of the study,

“This discovery reshapes our understanding of how speech is processed in the brain, revealing an earlier and more complex role for Heschl’s gyrus in decoding meaning from subtle pitch variations.”

Unique Study with Real-Time Brain Recordings

To examine how the brain deciphers pitch variations in speech, the research team studied 11 adolescent epilepsy patients undergoing neurosurgery. These individuals had electrodes implanted deep in their brains, allowing precise intracerebral recordings—a rare opportunity in human communication research.

Participants listened to an audiobook recording of “Alice in Wonderland” while scientists tracked real-time brain activity. The results showed that Heschl’s gyrus processed pitch changes independently from word recognition, meaning it plays a direct role in assigning linguistic meaning to shifts in tone and emphasis.

Implications for AI, Speech Therapy, and Neurological Disorders

This breakthrough has far-reaching applications, including:

• Speech and language therapy: Could lead to better treatments for autism, stroke-related dysprosody, and language-based learning disorders.
• Artificial intelligence (AI): Enhancing voice recognition systems to better interpret tone, improving human-computer interactions.
• Neuroscience: Helps explain what makes human communication unique, as non-human primates do not abstract pitch in the same way.

Dr. G. Nike Gnanateja, co-author of the study, emphasized,

“Our brains create stable representations of pitch, even though they vary with every spoken sentence. Understanding this process could revolutionize speech technology and communication therapies.”

With this discovery, scientists now have a deeper understanding of the hidden layers of human speech perception, paving the way for next-generation AI and medical interventions for speech and language disorders.

More Information: Cortical processing of discrete prosodic patterns in continuous speech, Nature Communications (2025). DOI: 10.1038/s41467-025-56779-w