Rhythm in human languages is often expressed as repeated pairings of syllables with different emphasis (stress), as in the place name Apalachicola, (A-pa)(LA-chi)(CO-la). Because such binary groupings (feet) recur widely across languages, linguists view them as important building blocks of language prosody. One very common foot type (a trochee) combines two short syllables with initial emphasis (BA ba), and another common type (an iamb) pairs a short with a following long syllable, (ba baa). Linguists have hypothesized that the evolution of these foot types in language may have been shaped by two principles of auditory perception according to which (i) sound sequences that contrast volume tend to be perceived as loud-initial groupings (trochees), and (ii) sound sequences contrasting duration tend toward long-last groupings (iambs). These principles have been validated in studies that have tested the influence of volume and duration separately, using primarily non-speech sounds (for example, tones).
However, human language is more complex in that intensity (volume) and duration cues generally vary together, not separately. Moreover, other sound features, for example glottalization (laryngeal creakiness), are known to interact with stress groupings in language, although the influence of these cues on subjective grouping has not been tested with human subjects in speech perception studies. This project takes the next step with a series of speech perception experiments designed to study these issues. First, the influence on subjective grouping of jointly varying intensity and duration will be studied. Parallel experiments will study the influence of varying glottalization both in isolation, and in combination with duration. To study the issue of whether subjective grouping preferences based on the specific features studied are language specific or general, planned experiments will be conducted with native speakers of (Mexican) Spanish and Zapotec in addition to English. This work is expected to advance our understanding of how perceptual features that influence the cognitive activity of grouping may have helped to shape aspects of human language.
