Volume 113, Issue 3, March 2003
Index of content:
- SPEECH PERCEPTION 
113(2003); http://dx.doi.org/10.1121/1.1553464View Description Hide Description
Despite a lack of traditional speech features, novel sentences restricted to a narrow spectral slit can retain nearly perfect intelligibility [R. M. Warren et al., Percept. Psychophys. 57, 175–182 (1995)]. The current study employed 514 listeners to elucidate the cues allowing this high intelligibility, and to examine generally the use of narrow-band temporal speechpatterns. When -octave sentences were processed to preserve the overall temporal pattern of amplitude fluctuation, but eliminate contrasting amplitude patterns within the band, sentence intelligibility dropped from values near 100% to values near zero (experiment 1). However, when a -octave speech band was partitioned to create a contrasting pair of independently amplitude-modulated -octave patterns, some intelligibility was restored (experiment 2). An additional experiment (3) showed that temporal patterns can also be integrated across wide frequency separations, or across the two ears. Despite the linguistic content of single temporal patterns, open-set intelligibility does not occur. Instead, a contrast between at least two temporal patterns is required for the comprehension of novel sentences and their component words. These contrasting patterns can reside together within a narrow range of frequencies, or they can be integrated across frequencies or ears. This view of speech perception, in which across-frequency changes in energy are seen as systematic changes in the temporal fluctuation patterns at two or more fixed loci, is more in line with the physiological encoding of complex signals.
Quantitative evaluation of lexical status, word frequency, and neighborhood density as context effects in spoken word recognition113(2003); http://dx.doi.org/10.1121/1.1534102View Description Hide Description
Listeners identified a phonetically balanced set of consonant–vowel–consonant (CVC) words and nonsense syllables in noise at four signal-to-noise ratios. The identification scores for phonemes and syllables were analyzed using the j-factor model [Boothroyd and Nittrouer, J. Acoust. Soc. Am. 84, 101–114 (1988)], which measures the perceptual independence of the parts of a whole. Results indicate that nonsense CVC syllables are perceived as having three independent phonemes, while words show independent units. Among the words, high-frequency words are perceived as having significantly fewer independent units than low-frequency words. Words with dense phonetic neighborhoods are perceived as having 0.5 more independent units than words with sparse neighborhoods. The neighborhood effect in these data is due almost entirely to density as determined by the initial consonant and vowel, demonstrated in analyses by subjects and items, and correlation analyses of syllable recognition with the neighborhood activation model [Luce and Pisoni, Ear Hear. 19, 1–36 (1998)]. The j factors are interpreted as measuring increased efficiency of the perception of word-final consonants of words in sparse neighborhoods during spoken word recognition.
The effects of hearing loss on the contribution of high- and low-frequency speech information to speech understanding113(2003); http://dx.doi.org/10.1121/1.1553458View Description Hide Description
The speech understanding of persons with “flat” hearing loss (HI) was compared to a normal-hearing (NH) control group to examine how hearing loss affects the contribution of speech information in various frequency regions. Speech understanding in noise was assessed at multiple low- and high-pass filter cutoff frequencies. Noise levels were chosen to ensure that the noise, rather than quiet thresholds, determined audibility. The performance of HI subjects was compared to a NH group listening at the same signal-to-noise ratio and a comparable presentation level. Although absolute speech scores for the HI group were reduced, performance improvements as the speech and noise bandwidth increased were comparable between groups. These data suggest that the presence of hearing loss results in a uniform, rather than frequency-specific, deficit in the contribution of speech information. Measures of auditory thresholds in noise and speech intelligibility index (SII) calculations were also performed. These data suggest that differences in performance between the HI and NH groups are due primarily to audibility differences between groups. Measures of auditory thresholds in noise showed the “effective masking spectrum” of the noise was greater for the HI than the NH subjects.