Frequency Discrimination as Measured by AB and ABX Procedures

Rosenblith and Stevens reported in 1953 that difference thresholds for frequency measured by an ABX procedure were at least twice as great as those measured by an AX procedure. Their report is consistent with the great bulk of the literature. The relationship has always been rationalized in terms of the greater physical and judgmental complexity of the ABX procedure. The present experiment was performed at 120 cps, 70 dB SPL, with two practiced subjects. For frequency differences of plus or minus 0.3 cps, or one-fourth of 1%, responses were 95% correct for ABX and 82% correct for AB. This result contradicts the usual finding, and suggests a need for an experimental analysis of frequency-judgment mechanisms. The experimental data were collected at the Massachusetts Institute of Technology Research Laboratory of Electronics.