Academic journal article Perception and Psychophysics

Auditory Frequency Discrimination Learning Is Affected by Stimulus Variability

Academic journal article Perception and Psychophysics

Auditory Frequency Discrimination Learning Is Affected by Stimulus Variability

Article excerpt

We explored the effects of training set variability on learning and generalization of pure-tone frequency discrimination (FD) in three groups of untrained, normally hearing adult listeners. Group 1 trained using a fixed standard tone at 1 kHz (fixed), Group 2 on slightly varying (roving) tones around 1 kHz, and Group 3 on widely varying standard frequencies (wide-roving). Initially, two thirds of all listeners had low FD thresholds (good listeners) and one third had intermediate to high thresholds (poor listeners). For good listeners, slight variations in the training set slowed learning but wide variations did not. Transfer to untrained frequencies (up to 4 kHz) and to the fixed condition was equivalent regardless of training condition, but Group 1 listeners did not fully transfer learning to the roving condition. For poor listeners, any variation in the training condition slowed learning and impaired transfer to other frequencies but did not affect transfer to untrained conditions. Thus, the effects of training set on progress and outcome depend on set variability and individual FD ability.

The study of perceptual learning (see Gibson, 1953, 1963, and Goldstone, 1998, for definitions and reviews) may have great applicability; various forms of auditory discrimination training contribute to improving children's language abilities (Merzenich et al., 1996; Tallal et al., 1996) and reading skills (Kujala et al., 2001) and to reducing the severity of tinnitus (Flor, Hoffmann, Struve, & Diesch, 2004). However, although the list of training benefits is rapidly expanding, the variables and mechanisms affecting auditory learning are still poorly understood.

Discrimination of a frequency difference between two sequentially presented pure tones has been the most extensively used task in laboratory studies of auditory perceptual learning, perhaps because consistent and robust improvement has been seen in every study (Delhommeau, Micheyl, Jouvent, & Collet, 2002; Demany, 1985; Demany & Semal, 2002; Grimault, Micheyl, Carlyon, Bacon, & Collet, 2003; Grimault, Micheyl, Carlyon, & Collet, 2002; Irvine, Martin, Klimkeit, & Smith, 2000). Other tasks, such as sound lateralization (Wright & Fitzgerald, 2001) and temporal-interval discrimination (Karmarkar & Buonomano, 2003; Wright, Buonomano, Mahncke, & Merzenich, 1997), have also been used. The common approach has been to pretest listeners on several conditions of interest, provide training on a single condition, and then retest on the original set of conditions to check for improvement. Improvement on untrained conditions is considered evidence for generalization, or transfer, of learning. Conclusions regarding the type and underlying mechanisms of learning are then drawn from the pattern of transfer. Thus, Demany (1985) showed that frequency discrimination (FD) learning transfers to untrained frequencies within the range mediated by the same mechanism (temporal coding at low frequencies, place coding at high frequencies) but that it does not transfer across frequency ranges, whereas Irvine et al. (2000) showed that a small component of learning is specific to the trained frequency, even within the same frequency range. Delhommeau et al. (2002) showed that a large part of FD learning transfers to the untrained ear and across tone durations but that a smaller component is duration- and ear-specific. These studies suggest that tone discrimination learning has separable components, each providing evidence for a locus of operation.

A second approach acknowledges that the acoustic environment is constantly changing and that tones are rarely heard in isolation. Watson, Kelly, and Wroton (1976) reviewed a number of studies of the discrimination of two sequences often tones in which the frequency of a single target tone varied within the sequence. After extensive training, the FD of the target tone was only slightly worse than that for the same tone presented in isolation (as in the studies above), but only when the training sequence was fixed and the target tone had the same temporal position in the sequence. …

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