Frequency discrimination training: is there ear symmetry?

While it is well documented that significant improvements in a frequency discrimination task occur following training of normal-hearing adult subjects, less is known about the symmetry between the ears. The objectives of the present study were (1) to compare the first obtained DLF thresholds between left and right ears, (2) to determine whether single-session training would result in similar improvements in those subjects trained in the right ear versus those trained in the left ear, and (3) to evaluate the generalization of learning to the untrained ear and compare its extent between the left and right ears. Two groups of 10 normal-hearing subjects participated in a single-session training. One group of 10 subjects was trained in the left ear and the second group of 10 additional subjects was trained in the right ear. Single-session training consisted of 10 difference limen frequency (DLF) thresholds for 1 kHz using a two-interval, two-alternative forced choice paradigm. Generalization to the untrained ear was tested 24 hours post-training. Our results show that: (1) No significant differences were found in the first obtained DLF thresholds between left and right ears; (2) Similar improvement in DLF thresholds occurred in both ears for single-session training; and (3) Twenty-four hours post-training, learning generalized to the untrained ear with similar generalization to both ears. Future studies are required in order to establish whether this symmetry is maintained with verbal stimuli and/or after multi-session training.