Temporal properties of perceptual calibration to local and broad spectral characteristics of a listening context.

The auditory system calibrates to reliable properties of a listening environment in ways that enhance sensitivity to less predictable (more informative) aspects of sounds. These reliable properties may be spectrally local (e.g., peaks) or global (e.g., gross tilt), but the time course over which the auditory system registers and calibrates to these properties is unknown. Understanding temporal properties of this perceptual calibration is essential for revealing underlying mechanisms that serve to increase sensitivity to changing and informative properties of sounds. Relative influence of the second formant (F(2)) and spectral tilt was measured for identification of /u/ and /i/ following precursor contexts that were harmonic complexes with frequency-modulated resonances. Precursors filtered to match F(2) or tilt of following vowels induced perceptual calibration (diminished influence) to F(2) and tilt, respectively. Calibration to F(2) was greatest for shorter duration precursors (250 ms), which implicates physiologic and/or perceptual mechanisms that are sensitive to onsets. In contrast, calibration to tilt was greatest for precursors with longer durations and higher repetition rates because greater opportunities to sample the spectrum result in more stable estimates of long-term global spectral properties. Possible mechanisms that promote sensitivity to change are discussed.