Measuring differential nodal distance using the function acquisition speed test

Increasing evidence suggests that the relatedness of stimuli within the Function Acquisition Speed Test (FAST) methodology is sensitive to the learning histories of participants. For example, this method is sensitive to differences in the amount of baseline training provided to establish stimulus equivalence relations using arbitrary stimuli (Cummins et al., 2018a). However, it has not yet been investigated whether the relatedness of stimuli within the FAST varies based on differential nodal distances between stimuli within stimulus classes. If so, the FAST could serve an important adjunct assessment procedure for researchers who wish not only to assess the formation of stimulus classes using traditional methods, such as matching-to-sample, but also the relative relatedness of stimuli within complex stimulus classes (i.e., nodal distance). The current study sought to investigate this possibility. Participants (n = 16) were trained in the formation of two 4-member equivalence classes consisting of arbitrary nonsense syllables. Following this, participants completed three FAST assessments, each of which probed for the relatedness of stimulus pairs of differing nodal distance. Group- and individual-level analyses broadly demonstrated that relatedness varied as a function of nodal distances in pre-trained stimulus classes. However, results also highlighted some limitations of the FAST at the individual level.