Haimson, B., Wilkinson, K.M., Rosenquist, C., Ouimet, C. & McIlvane, W.J. (2009).
Electrophysiological correlates of stimulus equivalence processes.
Journal of the Experimental Analysis of Behavior, 92, 245-256.
Research reported here concerns neural processes relating to stimulus equivalence class formation. In Experiment 1, two types of word pairs were
presented successively to normally capable adults. In one type, the words had related usage in English (e.g., uncle, aunt). In the other, the two words
were not typically related in their usage (e.g., wrist, corn). For pairs of both types, event-related cortical potentials were recorded during and
immediately after the presentation of the second word. The obtained waveforms differentiated these two types of pairs. For the unrelated pairs, the
waveforms were significantly more negative about 400 ms after the second word was presented, thus replicating the "N400" phenomenon of the cognitive
neuroscience literature. In addition, there was a strong positive-tending wave form difference post-stimulus presentation
(peaked at about 500 ms) that also differentiated the unrelated from related stimulus pairs. In Experiment 2, the procedures were extended to study
arbitrary stimulus–stimulus relations established via matching-to-sample training. Participants were experimentally naive adults. Sample stimuli
(Set A) were trigrams, and comparison stimuli (Sets B, C, D, E, and F) were nonrepresentative forms. Behavioral tests evaluated potentially emergent
equivalence relations (i.e., BD, DF, CE, etc.). All participants exhibited classes consistent with the arbitrary matching training. They were also
exposed also to an event-related potential procedure like that used in Experiment 1. Some received the ERP procedure before equivalence tests and some
after. Only those participants who received ERP procedures after equivalence tests exhibited robust N400 differentiation initially. The positivity
observed in Experiment 1 was absent for all participants. These results support speculations that equivalence tests may provide contextual support for
the formation of equivalence classes including those that emerge gradually during testing.
Key words:equivalence, arbitrary matching, N400, mouse click, normally capable adult