5.2 Auditory (Ga), speech,and language prominence in temporal processing
Temporal information in the range of tens to hundreds of ms is fundamental to many forms of sensory processing. Motion processing is a ubiquitous example in the auditory, somatosensory, and visual domains of a task that requires temporal information. However, it is arguably in the auditory domain that timing is most prominent, owing to its importance in vocalization and speech recognition.
The temporal structure within each syllable and phoneme also contributes to speech recognition. Specifically, temporal features are fundamental for phoneme discrimination. These features include voice- onset time (the time between air release and vocal cord vibration), which contributes to the “ba” × “pa” discrimination (Lisker & Abramson 1964), the duration of frequency transitions (e.g., “ba” × “wa”; Liberman et al. 1956), and the silent time between consonants and vowels (e.g., “sa” × “sta”; Dorman et al. 1979). Additionally, prosodic cues such as pauses and duration of speech segments are used to determine semantic content (Lehiste et al. 1976).
Owing to the multiple levels and scales of temporal information in addition to spatial information, speech is one of the most complex forms of pattern recognition and requires both spatial and temporal processing (Shannon et al. 1995,Tallal 1994, Doupe & Kuhl 1999). Various lines of evidence have revealed the degree to which speech recognition relies on temporal information. Indeed, in some cases it canrely primarily on the temporal structure.
Given the importance of temporal information in speech and language it would be expected that deficits in temporal processing would produce language deficits. Indeed, it has been suggested that certain forms of language-based learning disabilities may be caused by generalized sensory deficits in temporal processing (Livingstone et al. 1991, Eden et al. 1996, Tallal & Piercy 1973; for a review seeFarmer & Klein 1995).