Niklaus Wirth designed Pascal (1970) with explicit pedagogical and human factors goals documented in his seminal paper "On the Design of Programming Languages". Wirth explicitly stated his belief that "insights gained from educational considerations could benefit programming language design in general, and that the simplicity and clarity he was striving for should be a guiding principle for all language design, serving equally pedagogical and development purposes". But - as with Ada - I'm not aware of any notable human factors engineering studies to validate design decisions.
Also Alan Kay and the Xerox PARC team designed Smalltalk (as Papert did before with Logo) with profound human-centered considerations, and they even "tested" their early concepts with children.
Also some other languages explicitly state human-centered design goals (e.g. Python, Eiffel), but as with Pascal or Ada the approach was more based on expert judgment, formal analysis, and established principles, not practical studies.
