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Signal detection theory separates sensitivity from bias. Sensitivity d prime is the difference between the z-transformed hit rate and false alarm rate: 84% hits against 12% false alarms gives d prime 2.17. Raw accuracy of 86% would conflate the two, hiding whether the participant is genuinely discriminating or simply cautious.
Sensitivity
d' = z(hit rate) - z(false alarm rate)
Response bias
c = -0.5 x (z(hit rate) + z(false alarm rate))
Because accuracy mixes discrimination with willingness to respond. Someone who says yes to everything scores well on hits and terribly on false alarms.
Negative values indicate a liberal bias towards responding yes, positive values a conservative bias. Zero is unbiased.