Grouping and adaptation in modulation detection interference

Abstract

Modulation detection interference (MDI) can be reduced by gating the masker and signal carriers asynchronously, possibly due to grouping effects. However, as both carriers are generally modulated throughout their presentation, two other factors may also play a role: First, the response to modulation may adapt, thereby reducing the effective masker modulation depth prior to signal presentation. Second, analogous to intensity perception, a dynamic change in modulation depth (increment detection) may be easier to detect than an overall difference across two presentations (level discrimination). A MDI paradigm with 1- and 4.3-kHz carriers was used. The 16-Hz sinusoidal signal modulation was masked by noise modulation with a passband from 8 to 24 Hz. In one experiment, the gating synchrony of carrier and modulator were independently varied. In another experiment, both masker and signal modulated a single 4.3-kHz carrier, with gating synchrony between masker and signal varied. Results suggest that the asynchronous gating of either the carriers or modulators alone is not sufficient to produce a release from MDI. Thresholds were higher for the single carrier than for the two carriers, and gating the masker modulation on prior to the signal did not improve performance. [Supported by NIDCD and Max Kade Foundation.]