Ch. 5 From Perception to Pleasure

Chapter 5: Hemispheric Specialization: Two Brains Are Better Than One

Introduction to Hemispheric Specialization

• Nobel Prize in 1981: Roger Sperry awarded for discoveries of functional specialization in the cerebral hemispheres.

• Significant recognition of how brain halves differ in functions, particularly in music processing.

• Historical context of hemispheric function: Paul Broca's 1860s work on language disorders related to left hemisphere damage.

• Marc Dax (1836) and language asymmetries discovered in aphasic patients and historical observations linking musical functions to language.

Historical Cases

• Vissarion Shebalin:

  • Soviet composer with profound aphasia from a left-hemisphere stroke, continued to compose music.

  • Represents the idea that advanced musical function can exist independently of language.

• Jean Langlais:

  • French organist who maintained abilities to perform and compose post left-hemisphere damage.

  • Indicates the complex relationship between music and language processing.

Limitations of Case Studies

• The anecdotal nature of individual cases prevents the formulation of a strong theoretical framework with predictive validity.

• Variability of aphasia cases complicates understanding of the interaction between music and language.

Theoretical Models

• Models struggled to define clear lateralization links; some suggested:

  • Language = Left Hemisphere

  • Music = Right Hemisphere

• Dominant Hemisphere Concept: Implies cognition tied mainly to language processes in the left hemisphere.

• Emphasis on unique contributions of each hemisphere makes previous models inadequate.

Research Method Changes

• Brenda Milner’s 1962 study: Shift from descriptive case studies to experimental design testing separate musical abilities like pitch, timbre, etc.

• Identified that right temporal excisions disrupted melody and timbre perception, suggesting left hemispheric functions are not primarily responsible for musical tasks.

Subsequent Findings

• Studies show:

  • Right hemisphere critical for tonal patterns and music analysis but left hemisphere more involved in language.

  • Asymmetries in auditory cortex function reflect differential processing of music versus language functions.

Differences in Processing: Music vs. Speech

Spectral Information Utilization

• Music: Discrete pitch steps and hierarchical structures facilitate predictive processes (e.g., tonality).

  • Predictable relations between pitches contribute to emotion and pleasure in music.

• Speech: Continuous pitch variation for prosodic and grammatical functions does not depend on specific pitch targets.

Speech to music Allusion

• anatomical associations: broca’s area, premotor cortex

Temporal Information Utilization

• Music: Highly structured rhythm and periodic beat are crucial; temporal cues for precise rhythm delineation.

• Speech: Temporal modulation rates are typically higher; integral for phonemes and syllables.

Neuroimaging Results

• Functional neuroimaging shows:

  • Right auditory cortex responds more to spectral changes (fine-tuned spectral features necessary for music).

  • Left auditory cortex more engaged with temporal changes reflecting speech processing.

• Tradeoff hypothesis: Specialization of one auditory dimension (temporal or spectral) trades off with the other’s processing ability.

Genetic and Evolutionary Context

• Human auditory systems optimized for different communicative intents—music and speech reflect functional use of acoustical cues in context.

• Helps explain why individuals engage different hemispheres based on task requirements, training, and familiarity.

Conclusion

• Hemispheric optimization: Evidence strongly supports differentiated spectral (right hemisphere) and temporal (left hemisphere) processing.

• Lateralization reflects how music and speech exploit sound features distinctly, enhanced by both genetics (evolution) and environment (cultural communication).

Future Directions

• Need for more detailed understanding of how top-down cognitive factors can influence these specialized processes dynamically through task demands.