Individual differences in spectral temporal order judgment are associated with temporal fine structure processing

Temporal order judgment (TOJ) for two brief tones with different frequencies is commonly used to assess auditory temporal resolution. Participants can be classified as high-, mid-, and low-level performers (HLP, MLP, LLP) based on the pattern of the results. The present study examined whether variability in the use of temporal fine structure (TFS) cues at the output of auditory filters centered between the frequencies of the two tones contributes to the individual differences. HLPs show high accuracy even when the inter-stimulus interval (ISI) is very small, MLPs show accuracy that increases with increasing ISI, and LLP show poor performance for all ISIs. Experiment 1 used a lower-frequency tone at 1 kHz with a variable upper-frequency tone. The prevalence of HLP decreased with increasing upper frequency, consistent with the reduction of neural phase locking at higher frequencies and the reduced salience of TFS cues with increasing frequency separation of the two tones. Experiment 2 used octave-spaced tones with a wide range of center frequencies. There was a progressive shift from HLP to MLP and LLP as the mean frequency increased. Experiment 3 directly manipulated TFS cue availability using narrowband noise centered between the frequencies of the two tones. This reduced the proportion of HLP and increased the proportion of MLP. These findings support the idea that differences between HLP and MLP for short ISIs reflect differences in the extent to which participants make use of TFS cues. LLP make poor use of both TFS cues and temporal sequence for this task.