ISCA Workshop on Plasticity in Speech Perception (PSP2005)

Senate House, London, UK
June 15-17, 2005

Identification Functions of /ba-pa/ Continua in Noise and their Relation to Open-Set Word Recognition in Noise

Liat Kishon-Rabin, Liat Noy, Noa Gubi

University of Tel-Aviv, Israel

Minka Hildesheimer University of Tel-Aviv Daphne Ari-Even Roth University of Tel-Aviv Difficulty of understanding speech in noise characterizes different populations, such as, children, hearing impaired, learning disabled and the elderly. In order to gain better insight to this problem, we investigated the effect of noise on what is considered the first stage of linguistic processing, that is, the stage at which the hearing system extracts the acoustic information from the physical signal and transforms it to mental representations of phonetic units. These units, also known as speech contrasts, are thought to be the basic building blocks of speech and are assumed to be minimally constrained by linguistic redundancy. The goals of the present study were, therefore: (1) to investigate the effect of background noise on the identification functions of Hebrew voicing in initial position along a continuum of voice-onset-time (VOT), and to compare these functions to those obtained in quiet, and (2) to examine the relationship between identification functions of voicing and word identification in noise. Fourteen normal-hearing, Hebrew-speaking, young adults participated in the study. Naturally produced stimuli consisted of: (1) a /ba-pa/ continuum which varied in VOT values from a lead of -100 ms to a lag of +50 ms in 10 ms steps, and were presented in quiet and in white noise at signal-to-noise ratios (SNR) of 0 and -3; and (2) one-syllable Hebrew AB word lists presented in SNR of 0 and +3. Subjects were asked to label the syllables as /ba/ or /pa/ and repeat the words they heard, respectively. Depended variables included category boundary (CB) at the 50% correct crossover point, the integral (areas) of the functions, and % word correct. Results show that with increasing level of background noise: (1) CB became more negative, i.e., syllables sounded more voiceless than voiced; (2) variability in performance increased among the subjects; (3) the areas under the identification functions decreased, more so for the voiced /ba/; and (4) 43% of the variance in open-set word performance in noise can be explained by the integral of the functions. These results suggest that the degrading effect of background noise is already evident at the very basic level of speech perception processing. It may contribute to our understanding of the difficulties that young children may encounter while forming mental representations of phonetic categories via a "noisy" system (internal noise produced by their impaired hearing system and/or external noise from hearing assistive devices and/or the environment).

Bibliographic reference.  Kishon-Rabin, Liat / Noy, Liat / Gubi, Noa (2005): "Identification functions of /ba-pa/ continua in noise and their relation to open-set word recognition in noise", In PSP2005, 231 (abstract).