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

Abstract

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.

Modest, reliable spectral peaks in preceding sounds influence vowel perception

“…Reliable spectral peaks consistently produced significant increases in tilt weights in Alexander and Kluender (2010), but the same was not observed here despite using the same target vowels. Two differences in experimental design might explain this discrepancy.…”

“…Wilcox's (2005) Minimum Generalized Variance method was used to remove all data for listeners whose weights for vowels presented in isolation were outliers, which complicates interpreting measures of perceptual calibration (n ¼ 2 in experiment 1; no outliers in experiment 2; n ¼ 3 in experiment 3). On the basis of previous experiments (Kiefte and Kluender, 2008;Alexander and Kluender, 2010), and if perceptual calibration effects extend to more modest amplitude manipulations, F 2 weights were predicted to decrease while tilt weights were predicted to increase for all conditions. Significant weight changes from baseline (i.e., weights for vowels presented in isolation) were of primary interest.…”

“…Target vowels were the same stimuli from Alexander and Kluender (2010), perceptually varying from [i] (as in "beet") to [u] (as in "boot"). Vowels were synthesized using the parallel branch of the Klatt and Klatt (1990) synthesizer at a sampling rate of 22 500 Hz.…”

“…In audition, when a spectral property is reliable (i.e., relatively stable or recurring in the acoustic spectrum, such as a particular spectral shape or local frequency peak) across a preceding acoustic context and subsequent vowel target, perception deemphasizes this cue and shifts toward other changing (thus more informative) cues for speech recognition. This process, known as auditory perceptual calibration, has been demonstrated for both spectrally local (second formant frequency, F 2 ) and global (overall spectral tilt) cues to vowel identity (Kiefte and Kluender, 2008;Alexander and Kluender, 2010). When acoustic energy in the vowel's F 2 region is made reliable throughout the preceding acoustic context, listeners attribute less weight to F 2 and more weight to spectral tilt in vowel identification, and vice versa.…”

“…In Kiefte and Kluender (2008) and Alexander and Kluender (2010), acoustic energy at the vowel's F 2 was made reliable in the precursor sound by amplifying this frequency region by 20 dB or more. Assmann and Summerfield (2004) suggested that perceptual compensation reported by Darwin et al (1989) may occur only under extreme conditions, since it was only present for 30-dB changes in spectral slope.…”