Amplitude modulation depth discrimination of a sinusoidal carrier: Effect of stimulus duration

Abstract

Discrimination of the change in depth of sinusoidal amplitude modulation (AM) was investigated as a function of stimulus duration. The carrier frequency was 4000 Hz, the standard modulation depth (m) was either 0.1, 0.18, or 0.3, and the modulation rate was either 10, 20, 40, or 80 Hz. For all standard depths and modulation rates, threshold (delta m) decreased by more than a factor o two as stimulus duration doubled from the shortest duration used up to a certain duration (critical duration), beyond which the threshold decreased only slightly or remained constant. The critical duration corresponded to about four cycles of modulation. Psychometric functions were measured for different stimulus durations to examine the extent to which a multiple-looks model could explain the present data. This model provided a reasonable prediction of the change in AM depth discrimination threshold as a function of stimulus duration.

Notched-noise precursors improve detection of low-frequency amplitude modulation

“…When averaged across carrier levels and subjects, the improvement in AM detection thresholds for long carriers compared to short carriers with a precursor was 2.1 dB for the current experiment, which is appreciably smaller than the 5 dB improvement predicted by multiple looks. Lee and Bacon (1997) reported a critical duration of $4 cycles for AM detection using sinusoidal carriers modulated at 20 Hz. This suggests that although ten cycles of the long carrier were available to listeners, only four of these cycles contributed to improvements in thresholds compared to thresholds for short carriers with a precursor.…”

A computational model of human auditory signal processing and perception

“…Several studies of modulation depth discrimination ͑e.g., Wakefield and Viemeister, 1990;Lee and Bacon, 1997;Ewert and Dau, 2004͒ showed that Weber's law holds for most modulation depths, i.e., the JND of AM depth is proportional to the reference modulation depth. A modified internal-noise source would be required in the model to account for these data ͑Ewert and Dau, 2004͒.…”

Contribution of onset/offset information of modulation to amplitude modulation depth discrimination

“…Thresholds were similar for both gated and continuous carrier conditions for modulation cycles greater than four. These results suggest that a difference in stimulus gating may have caused the absence of a critical duration effect in AM detection observed from the comparison of data from Sheft and Yost (1990) and Lee and Bacon (1997). For the gated carrier condition, shaping the onset/offset of stimuli with rise/fall times might reduce modulation information at the onset/offset, which might result in a dramatic change in threshold for a smaller number of modulation cycles.…”

“…In contrast, AM detection thresholds were found to decrease gradually with increasing duration from 25 to 400 ms. It should be noted, however, that Sheft and Yost (1990) used the noise carrier whose total duration was 51.2 ms longer (due to 25.6 ms rise/fall time) than modulation duration, while Lee and Bacon (1997) used a gated sinusoidal carrier. This difference between stimuli led to the study of Lee et al (2006) in which both AM detection and AM depth discrimination were measured with the same stimulus conditions.…”

“…There was a critical duration of four cycles of modulation in which a dramatic threshold improvement (more than factor of 2) was observed when the stimulus duration increased from a shorter duration to this critical duration; only a slight or no improvement of threshold was observed when the stimulus duration exceeded this critical duration for modulation rates of 10, 20, 40, and 80 Hz. Lee and Bacon (1997) compared AM detection data (Sheft and Yost, 1990) with their AM depth discrimination data and found that AM detection lacks the critical duration effect observed in AM depth discrimination. In contrast, AM detection thresholds were found to decrease gradually with increasing duration from 25 to 400 ms.…”