UCSF

Discrimination between spoken words composed of overlapping elements, such as "captain" and "captive," relies on sensitivity to unique combinations of prefix and suffix elements that span a "uniqueness point" where the word candidates diverge. To model such combinatorial processing, adult female zebra finches were trained to discriminate between target and distractor syllable sequences that shared overlapping "contextual" prefixes and differed only in their "informative" suffixes. The transition from contextual to informative syllables thus created a uniqueness point analogous to that present between overlapping word candidates, where targets and distractors diverged. It was found that target recognition depended not only on informative syllables, but also on contextual syllables that were shared with distractors. Moreover, the influence of each syllable depended on proximity to the uniqueness point. Birds were then trained birds with targets and distractors that shared both prefix and suffix sequences and could only be discriminated by recognizing unique combinations of those sequences. Birds learned to robustly discriminate target and distractor combinations and maintained significant discrimination when the local transitions from prefix to suffix were disrupted. These findings indicate that birds, like humans, combine information across temporally distributed features, spanning contextual and informative elements, in recognizing and discriminating word-like stimuli.