The relation between stimulus function and equivalence class formation.
Stimuli that already share a job slow equivalence class formation, so pick items with unique roles.
01Research in Context
What this study did
Researchers gave adults simple discrimination training. Then they tested if the items would form equivalence classes.
Some items already did the same job in the lab. Others did different jobs. Some were brand new.
What they found
Items that shared a job took many extra trials to join a class. Items with different jobs or new items formed classes quickly.
Overlap in what the stimuli 'do' slows the linking process.
How this fits with other research
Davison et al. (1984) got clean, fast equivalence with kids using neutral pictures. Their positive result looks opposite to the 2004 slow-down, but both used matching-to-sample. The difference is the 1984 team picked items with no shared function.
Sigurðardóttir et al. (2012) also saw quick, error-free classes with Icelandic words. Again, the words had no prior use in the lab, so no function overlap got in the way.
Jennings et al. (2017) formed classes with just tact and intraverbal drills. They did not even run matching-to-sample first. Their success shows that when you remove shared stimulus functions, equivalence can emerge through talk alone.
Why it matters
Before you start equivalence lessons, audit your stimuli. If two pictures both signal 'break' or 'help', split them into different classes or swap one out. Pick items that only serve the new role you are teaching. You will save trials and cut learner frustration.
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02At a glance
03Original abstract
Fifty participants were exposed to a simple discrimination-training procedure during which six S+ functions were established for six arbitrary stimuli, and S- functions were established for a further six stimuli. Following this training, each participant was exposed to one of five conditions. In the S+ condition, participants were exposed to a stimulus equivalence training and testing procedure using only the six S+ stimuli as samples and comparisons. In the S+/S- condition, participants were exposed to the same training and testing sequence as in the S+ condition, the difference being that three S+ and three S- stimuli were used as sample and comparison stimuli, with each set of three corresponding to the trained equivalence relations. In the S+/S- mixed condition, the S+ and S- stimuli were assigned to their roles as samples and comparisons in a quasi-random order. In the S- condition, all six S- stimuli were used. The no-function condition served as a control condition and employed stimuli for which no stimulus-control functions had been established. The results showed that, on average, participants required more testing trials to form equivalence relations when the stimuli involved were functionally similar rather than functionally different. Moreover, participants required more test trials to form equivalence relations when novel arbitrary stimuli, rather than functionally distinct stimuli, were used as samples and comparisons. The speed of acquisition of stimulus equivalence was also related to the number of functionally similar stimuli established before training. These findings indicate a variety of ways in which the emergence of equivalence relations is affected by the functional classes in which the relevant stimuli participate.
Journal of the experimental analysis of behavior, 2004 · doi:10.1901/jeab.2004.81-257