Campbell, J. D. & Clark, J. M. (1988). An encoding-complex view of congintive number processing: comment on McClosky, Sokol, and Goodman (1986). Journal of Experimental Psychology: General, 117, 204-214.
Dehaene, S., Bossini, S., & Giraux, P. (1993). The mental representation of parity and number magnitude. Journal of Experimental Psychology: General, 122, 371-396.
Gonzalez, E. G. & Kolers, P. A. (1982). Mental manipulation of arithmetic symbols. Journal of Experimental Psychology: Learning, Memory, and Cognition, 8 (4), 308-319.
Knoblich, G. & Haider, H. (1996). Empirical evidence for constraint relaxation in insight problem solving. Proceedings of the Eighteenth Annual Conference of Cognitive Science Society, 580-585. Hillsdale, NJ:, Lawrence Erlbaum Asspciates.