Presented at the 20^th Annual Meeting of the Hellenic Society for Neuroscience, Heraklion, Crete, Greece, 28 September–1 October 2006

Recent studies demonstrate perceptual learning of unattended stimuli that precede or predict the explicit task target. Implicit learning has improved visual coherent motion detection thresholds [1–3] and auditory categorization of artificial structured sound groups [4]. Based on these findings, we attempted to train Greek listeners to distinguish a Hindi dental-retroflex stop consonant contrast without task awareness or feedback, extending previous findings [5] challenging the standard assumption that non-native speech categories are learned by adults only when trained in focused attention with explicit feedback. Perceptual pre-tests indicated that Greeks are initially unable to differentiate the two Hindi categories but can learn the contrast with standard training. Subjects engaged in a demanding voice identification task in ten daily sessions. They heard rapid Greek syllable sequences in a variety of voices and had to repeat the syllable pronounced by one of two target voices. Hindi syllables with retroflex sounds, spoken by a single native speaker, always preceded the target voices, while Hindi dentals appeared in non-predictive positions. After training, subjects were tested in dental-retroflex discrimination and identification, and were compared to untrained Greek listeners. To test whether learning is a result of mere exposure to the Hindi sounds, control groups are tested with the same materials except for the co-occurrence of Hindi retroflex with the task target.

References
[1] Watanabe T et al., Nature, 413: 844–848. 2001.
[2] Watanabe T et al, Nature Neurosci, 5, 1003–1009, 2002.
[3] Seitz AR & Watanabe T, Nature, 422, 36, 2003.
[4] Wade T & Holt LL, J Acoust Soc Am, 118, 2618–2633, 2005.
[5] McCandliss BD et al., Cogn Affect Behav Neurosci, 2, 89–108, 2002.