Expansion of arbitrary stimulus classes and function-transfer measured by sorting performances.

Area of Science:

• Behavioral Psychology
• Learning and Cognition
• Stimulus Control

Background:

• Arbitrary stimulus classes are fundamental to complex cognition.
• Sorting (SRT) and matching-to-sample (MTS) tests are established methods for assessing stimulus class formation.
• Understanding the limits and expansion of these classes is crucial for cognitive research.

Purpose of the Study:

• To document the expansion of arbitrary stimulus class size using SRT and MTS tests.
• To investigate whether the sequence of SRT and MTS tests influences class expansion.
• To assess class expansion in participants who initially formed smaller classes.

Main Methods:

• Thirty-two participants learned conditional discriminations in a linear series (A➔B➔C➔D➔E).
• Sorting tests (SRT) and matching-to-sample (MTS) tests were employed to assess stimulus class formation and expansion.
• Training structures included forward chaining (FC) for 6-member classes and backward chaining (BC) for 4-member classes.

Main Results:

• SRT tests confirmed the formation of 5-member stimulus classes in 17 participants.
• Class expansion to 6 members was documented in 9 of these participants using sequential SRT and MTS tests.
• All 15 participants who did not form 5-member classes successfully expanded to 4-member classes, with high correspondence between SRT and MTS performance.

Conclusions:

• Sorting tests are effective in documenting the expansion of arbitrary stimulus classes.
• The sequence of SRT and MTS testing did not impact the observed class expansion.
• MTS tests confirmed that expanded stimuli function as members of equivalence classes.