Abstract:

It is clear that the ability to detect amplitude modulation (AM) is related to intensity resolution but the nature of this relationship is unclear. To address this issue, increment thresholds and modulation detection thresholds were measured under comparable conditions using the same subjects. The pedestal/carrier was a 1-kHz tone presented continuously throughout each block of trials. To ensure a substantial range of thresholds, the level of the pedestal/carrier was varied over a wide range (6--85 dB SPL). The duration of the increment and of the AM was 500 ms. Sinusoidal AM at a modulation frequency of 4 Hz was used. At this low frequency, modulation detection presumably was not affected by temporal resolution. As expected, the observed thresholds decreased with increased pedestal/carrier level. Over the range of measured modulation thresholds (about -33 to -5 dB, in 20 log m), the following well-describes the data: 10 log((Delta)I/I)=0.5(20 log m)+3, where (Delta)I/I is the Weber fraction for increment detection and m is the modulation index at modulation threshold. The generality of this relationship and its theoretical interpretation will be discussed. [Work supported by Grant No. DC00683 from NIDCD, NIH.]