Bilateral component in speech perception?

Abstract

The selective adaptation method was used to investigate the location of speech-related property detectors in the brain. A series of synthetic consonant-vowel syllables, ranging from [b æ] to [d æ], was used for testing the position of the phoneme boundary before and after adaptation. There were three main findings: (1) It was possible to simultaneously fatigue the “B-detectors” in one ear and the “D-detectors” in the other. (2) There was about 55% interaural transfer of adaptation. (3) When components of the adapting stimuli were presented in either binaurally fused or unfused conditions, the adapting effect was greater in the former case. These results are interpreted as showing that some component of speech processing may be performed on both sides of the brain, and that some component is performed after the point of binaural fusion. These two components are not necessarily based on different neural structures. The types of models considered were a two-tiered model postulating relatively peripheral mechanisms driven entirely monaurally, and a one-tiered model assuming that all adaptation takes place beyond the point of binaural fusion in structures which receive input from both ears, but more from one ear than from the other.