Pair Threshold Research Articles

Temporal processing of paired clicks: monaural and binaural summation at threshold

The threshold reduction that results from presenting the second of two equally intense clicks to either the same or the other ear after a brief interval (Δt) was measured using a three-interval forced-choice technique. The difference between thresholds for single clicks and click pairs randomized in the same session were measured monaurally for nine listeners and binaurally for 15 listeners. Summation of either monaural or binaural clicks was consistently less than would be predicted by a model of perfect energy summation, which concours with other studies using noise bursts of variable duration. The threshold reduction for a pair of monaural clicks was 2 dB at a Δt of 2 msec and even smaller reductions were obtained at longer Δt's. The threshold reduction for a pair of binaural clicks was 1.5 dB at interaural Δt's ranging from 0.01 to 15 msec. At Δt's ranging from 30 to 200 msec the threshold reductions for both binaural and monaural click pairs agreed with the level predicted by Green and Swets's “integration model” for the case of two independent observations.

Dynamic properties of vision—IV: Thresholds of decremental flashes, incremental flashes and doublets in relation to flicker fusion

The following were measured: the thresholds of pairs of incremental and decremental flashes as a function of their duration, those of doublets as a function of the flash interval and those of incremental flashes over a very large range of durations. The measurements constitute a coherent test of a model based on general system properties. The incremental and decremental threshold characteristics do not differ significantly, from which it is concluded that the excursion of the system responses to the flashes in the positive and negative direction must be approximately equally large if the flashes are to be detected. The doublet characteristics confirm that the response to short flashes contains a definite second phase. At low and high levels, however, they are practically isomorphous, which represents a deviation from the characteristics calculated from the De Lange flicker fusion curves. Measurements over a large range of durations show that under certain conditions the threshold characteristics of rectangular increments display a minimum and that they are remarkably isomorphous at low and high levels. This minimum was also not predicted from the De Lange characteristic. A refinement of the model introduced in order to explain these results yields a transmission curve which differs from the De Lange characteristics in the direction of greater attenuation at the very low frequencies and which, on the basis of the results referred to above, is also isomorphous for the various background levels.

Thresholds for click pairs masked by band-stop noise.

The auditory threshold was measured for a pair of clicks in the presence of band-rejected masking noise. This threshold depends on the interval between the two clicks. As the interval is changed, the threshold intensity alternately increases and decreases. For homopolar clicks and masking noise with a spectral gap centered at f Hz, maxima are at (2n +1)/(2f) sec (n = 0,1,2,…). Experimental determinations of this fluctuation, for equal-intensity clicks, are in quantitative agreement with predictions of a simple model. In the model, band-stop noise produces a band pass filtering of the click stimulus, and the stimulus is detected if the long-time average energy at the filter output exceeds some threshold value. However, if the clicks are of unequal intensity, the threshold is influenced by the click order. This order effect is inconsistent with the energy-detection model.