Cortical responses of 7-10-year-old children to easy and difficult contrasts in discrimination of pseudowords

Abstract

Brain responses of 7-10-year-old Finnish children to two speech contrasts incorporated in pseudowords (PWs) and varying in perceptual difficulty were studied. An oddball paradigm was used to record event-related potentials (ERPs) to a standard PW /baka/ and two deviant PWs: the easier = /baga/ and the more difficult /bag*a/ that sounded as intermediate between /baka/ and /baga/. An ability of children to actively discriminate the more difficult contrast was investigated in two separate behavioral sessions that alternated with the ERP recording blocks. The enhanced amplitude of the most negative response to the standard, not to the deviants, suggested formation of an acoustic template for the frequent PW during the experiment. There was no reliable block effect on the amplitude of the mismatch negativity (MMN), an automatic index of an experience-dependent auditory memory trace. This suggests consolidation of the short-term representation of the repetitively presented PW that took place during passive exposure to stimuli, rather than changes in the preattentive discrimination process. This was also supported by the evidence from a behavioral discrimination test. No perceptual learning to discriminate the difficult speech contrast could be seen in the children in the absence of the active behavioral discrimination.