By corollary, sounds with the same RT are interpreted to be equally loud. A broad assumption of these paradigms is that louder sounds generate shorter response latencies. Consequently, psychophysicists have sought tractable measures of loudness in the form of reaction time (RT) matching procedures (Miller et al. Neither approach translates well to common animal behavioral methodologies. Subjects can be asked to rank a stimulus on a perceptual scale (Stevens and Guirao 1963), or to match it to a reference sound (Fletcher and Munson 1933). In studies of human perception, methods for the quantification of subjective loudness are straightforward. These findings support the adequacy of the domestic cat as a model system for future investigations of the auditory processes that underlie loudness perception, recruitment, and hearing aid design.Īlthough loudness is related to the physical characteristics of sounds, especially their energy, it is a psychological attribute that is strongly shaped by how the energy is transduced, filtered, and integrated over time (Plack and Carlyon 1995). Vowels produced more recruitment than tones, and the effect was exacerbated by the selective amplification of formant structure. The effects of speech spectra and amplification on recruitment were explored by measuring the growth of loudness for natural and amplified vowels before and after sound exposure. Linear hearing aid amplification is known to improve speech intelligibility but also exacerbate recruitment in impaired listeners. Observed recruitment effects were similar in magnitude to those that have been reported in hearing-impaired humans. At the completion of normal baseline measures, the cats were exposed to intense sound to investigate the behavioral correlates of loudness recruitment, the abnormally rapid growth of loudness that is commonly associated with hearing loss. The resulting equal latency contours reproduced well-known features of human equal loudness contours. The psychophysical approach was based on the assumption that sounds of equal loudness elicit responses of equal latency. This study used a reaction time task to characterize loudness perception in six behaviorally trained cats. At present, there are no published descriptions of loudness perception in this species. The domestic cat is the primary physiological model of loudness coding and recruitment.
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