Abstract
BackgroundTime-compressed speech, a form of rapidly presented speech, is harder to comprehend than natural speech, especially for non-native speakers. Although it is possible to adapt to time-compressed speech after a brief exposure, it is not known whether additional perceptual learning occurs with further practice. Here, we ask whether multiday training on time-compressed speech yields more learning than that observed during the initial adaptation phase and whether the pattern of generalization following successful learning is different than that observed with initial adaptation only.Methodology/Principal FindingsTwo groups of non-native Hebrew speakers were tested on five different conditions of time-compressed speech identification in two assessments conducted 10–14 days apart. Between those assessments, one group of listeners received five practice sessions on one of the time-compressed conditions. Between the two assessments, trained listeners improved significantly more than untrained listeners on the trained condition. Furthermore, the trained group generalized its learning to two untrained conditions in which different talkers presented the trained speech materials. In addition, when the performance of the non-native speakers was compared to that of a group of naïve native Hebrew speakers, performance of the trained group was equivalent to that of the native speakers on all conditions on which learning occurred, whereas performance of the untrained non-native listeners was substantially poorer.Conclusions/SignificanceMultiday training on time-compressed speech results in significantly more perceptual learning than brief adaptation. Compared to previous studies of adaptation, the training induced learning is more stimulus specific. Taken together, the perceptual learning of time-compressed speech appears to progress from an initial, rapid adaptation phase to a subsequent prolonged and more stimulus specific phase. These findings are consistent with the predictions of the Reverse Hierarchy Theory of perceptual learning and suggest constraints on the use of perceptual-learning regimens during second language acquisition.
Highlights
Delivered speech is harder to comprehend than slower rate speech, and even more so for non-native speakers [1,2], older adults and individuals with hearing impairment [3]
The ability to identify time-compressed speech, an artificial form of fast speech, improves rapidly over the course of listening to as few as 10–20 sentences [4,5,6,7,8,9], the characteristics of learning and generalization beyond this initial adaptation phase have not been fully described. It is not even clear if practice beyond the adaptation phase yields additional learning because most studies on the perceptual learning of rapid speech focused on the adaptation period
Even experienced non-native listeners benefit from slower than normal speech rates [2,10]. These findings suggest that under ecological conditions, even prolonged and intensive experience does not result in native-like performance and can be taken to indicate that long-term perceptual learning of rapid speech is limited
Summary
Delivered speech is harder to comprehend than slower rate speech, and even more so for non-native speakers [1,2], older adults and individuals with hearing impairment [3]. The ability to identify time-compressed speech, an artificial form of fast speech, improves rapidly over the course of listening to as few as 10–20 sentences [4,5,6,7,8,9], the characteristics of learning and generalization beyond this initial adaptation phase have not been fully described. Naıve performance on timecompressed speech tasks is not poor due to inherent difficulties in encoding rapid speech, but rather because initial performance relies on high-level abstract acoustic representations and not on detailed low-level spectro-temporal representations of speech In this theoretical framework, perceptual learning, like perception, is a top-down driven process intended to locate the most relevant sensory representations. We hypothesize that multiday practice on a time-compressed speech task will result in additional perceptual learning to that reported after a brief adaptation phase, but this learning will be more stimulus specific and not generalize as broadly
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