A colleague of ours, whom with we shared the data from the published manuscript, identified an issue in our stimulus presentation during the phonetic categorization phase. While we believed that there were 8 repetitions of each of the 7 stimulus steps, a programming error lead to uneven distributions of each continuum step. Therefore, it is possible the effects we saw were due to selective adaptation and not lexically-guided perceptual learning.
The published data and analysis code are availalble in this repository under "Published Data".
We performed a corrected replication (with the intended stimulus distributions in the phonetic categorization phase) of the original experiment using the online platform Prolific. Experimental presentation was handled through Gorilla, which included two headphone checks to ensure that participants used roughly similar equipment to that which was used in the lab. 120 participants were recruited.
We allowed participants to begin session 2 at a minimum of 7 days (the average time between session 1 and 2 in SM2018) after their first session completed. As in SM2018, we only included participants who completed both sessions, and used the same accuracy criteria (minimum 80% accuracy at each endpoint during the phonetic categorization tasks) to exclude participants. In addition, we excluded any participant who failed both headphone checks. The resulting sample includes 63 participants.
In the published study, there were three main conclusions:
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A main effect of Bias - listeners show maximal flexibility when adapting to novel speech information, that is they will shift and reshift category boundaries as incoming phonetic information changes
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No Bias x Session interaction - listeners appear to use local statistics and do not aggregate talker-specific information over time, as there was no change in the bias effect from one session to another
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No Bias x Order interaction - the order of biasing blocks did not have an effect
In the replication, each of these conclusions changed in the following way:
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A main effect of Bias was found. We again found evidence of the main conclusion, which is that listeners will shift and reshift category boundaries as incoming phonetic information changes
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A Bias x Order interaction was found. That is, only participants who received the SH-S order showed evidence of shifting and reshifting their category boundaries, which is largely attributable to acoustic imbalances inherent in the fricatives produced in the original stimuli (see Drouin, Theodore, & Myers, 2015 for an explanation).
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A Bias x Order x Session interaction was found. This interaction was motivated by a decrease in the magnitude of the biasing effect for the SH-S order from session 1 to session 2. Therefore, it seems more likely that listeners are slowly aggregating statistics about the talker over time.
