Petitto’s research and discoveries span several scientific disciplines. Her early work with Nim Chimpsky and her later work with humans encompasses Anthropology, Comparative Ethology, Evolutionary Biology, Cognitive Neuroscience, Cognitive Science, Theoretical Linguistics, Philosophy, Psychology, Psycholinguistics, American Sign Language, Language Acquisition, Child Development, Evolutionary Psychology, Deaf Studies, Bilingualism, and Reading.
Her overall discoveries can be summarized:
- Cross-species (apes and humans) language and cognitive capacities
- The nature of early human language acquisition, structure, and representation in the human brain, and, crucially, the brain tissue that supports it
- The structure, grammar, and representation of natural signed languages of Deaf people, especially American Sign Language
- The nature of bilingual infants, children, and adults’ bilingual language and reading development, processing, and brain organization, with key comparisons to monolinguals
Petitto had a leading international role in the creation of a new scientific discipline that she and her colleagues have termed Educational Neuroscience (aka Mind, Brain and Education), involving the marriage of basic scientific discoveries about the developing brain/child with its principled application to solving core problems in the education of young children.
Taken together, the major contribution of her scientific writings have been to offer both testable hypotheses and theory regarding the neural basis for the brain’s specialization for human language, and how it is possible for very young babies to acquire language.
Using signed languages as a new “microscope” to discover the central/universal properties of human language in the brain (those that are distinct from the modality of language transmission and reception), Petitto advanced 5 branches of research.
Universal Linguistic Structures (cross-linguistic studies of signed and spoken languages and cross-linguistic studies of different signed languages, especially ASL and Langue des Signes Québécoise, LSQ
Linguistic Timing Milestones in Development (the highly similar maturational timing in the achievement of language milestones across young children acquiring spoken and signed languages)
Universal Linguistic Structures in Development (the highly similar acquisition of specific parts of natural language structure, with similar timing and use, across signed and spoken languages). For example, similar Pronouns, Pronominal Reference, and Pronoun-Reversals, across young children acquiring spoken and signed languages, despite the radically different linguistic form of pronouns in signed languages. The discovery of rhythmically-alternating, phonetic-syllabic “manual Babbling” on the hands in babies acquiring signed languages (be they Deaf or hearing), identical in linguistic structure, timing, and use to vocal Babbling in hearing babies acquiring spoken languages. For decades, Babbling was viewed as inextricably tied to sound and speech. However, the discovery of hand Babbling demonstrated that rather than sound being key, Babbling reflects the infant’s biologically-given sensitivity to highly specific patterns that are part of language structure. The discovery forced a reconceptualization of the nature of human Language by decoupling Speech and Language. Featured on both the cover of Science and the front page of the New York Times on the same day.
Distinct Knowledge Representation in Development (domain-specific versus domain-general knowledge in child development; the difference between language versus communicative gesture in all children’s development; the acquisition of pronominal reference, and pronoun reversals, versus gestures in young Deaf children acquiring ASL and young hearing children acquiring spoken language)
Brain Tissue Dedication for Aspects of Human Language Structure and Processing (convergences of specific linguistic functions on specific brain tissue across signed and spoken languages). For example, previously regarding spoken language, phonological processing was found to occur in the left hemisphere’s (LH) Superior Temporal Gyrus (brain tissue regarded as unimodal sound processing tissue for 125 years), and the Left Inferior Frontal Cortex was regarded as the brain’s site for the search and retrieval of information about word meanings (due to its proximity to LH speech production mechanisms). However, Petitto and her team found that the same brain tissue recruitment is used when processing the same parts of language regardless of whether the language was on the hands in signed language or the tongue in spoken language. Petitto is associated with advancing the new hypothesis (a new understanding) that this brain tissue is not neurally set to sound but instead to specific rhythmic-temporal patterns in maximal contrast –crucially, in ~1.5 Hertz temporal bursts – which are uniquely part of language phonetic-syllabic structure, which corroborated her earlier infant manual babbling discoveries and moved beyond “where” language processing occurs in the human brain to explain the nature of its underlying neural basis.
Sign Language As Real Languages
Petitto’s research has contributed to the body of knowledge establishing that the signed languages of Deaf people around the world are real languages with the full expressive capacity as spoken languages.
Petitto and colleagues were also the first to study experimentally the validity of a widely used educational practice with Deaf children in the 1970s, whereupon teachers (typically hearing) used parts of ASL signs and linguistic structure simultaneously while speaking English in the classroom, called “Total” or “Simultaneous Communication” (or “SimCom”). The Petitto team’s experimental study of SimCom with Deaf children demonstrated empirically that it was highly impoverished at representing either ASL or English (and, in turn, was a non-optimal teaching method), and instead supported the use of a natural language with Deaf children from early life (such as ASL), which would best provide a solid linguistic foundation upon which to learn other languages (such as English) and advanced the idea that Deaf Education would be best to move closer to a full bilingual/bicultural educational model. This research had lasting implications for subsequent Deaf Education policy and practice.