Temporal integration in amplitude modulation detection

Abstract

Thresholds for detecting sinusoidal amplitude modulation (AM) of a wideband noise carrier were measured as a function of the duration of the modulating signal. The carrier was either; (a) gated with a duration that exceeded the duration of modulation by the combined stimulus rise and fall times; (b) presented with a fixed duration that included a 500-ms carrier fringe preceding the onset of modulation; or (c) on continuously. In condition (a), the gated-carrier temporal modulation transfer functions (TMTFs) exhibited a bandpass characteristic. For AM frequencies above the individual subject's TMTF high-pass segment, the mean slope of the integration functions was - 7.46 dB per log unit duration. For the fringe and continuous-carrier conditions [(b) and (c)], the mean slopes of the integration functions were, respectively, - 9.30 and - 9.36 dB per log unit duration. Simulations based on integration of the output of an envelope detector approximate the results from the gated-carrier conditions. The more rapid rates of integration obtained in the fringe and continuous-carrier conditions may be due to "overintegration" where, at brief modulation durations, portions of the unmodulated carrier envelope are included in the integration of modulating signal energy.

Summary statistics in auditory perception

“…In most cases, however, performance on psychophysical tasks improves with stimulus duration, be it absolute detection 17 , frequency discrimination 18 , modulation detection 19,20 or localization 21,22 . Discrimination of textures with distinct statistical properties also improved with duration (experiment 1), as did discrimination of the temporal detail of single sources (experiments 4 and 5).…”

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.…”

“…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.…”

“…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.…”

“…Four carrier conditions were compared: Gated (carrier gated on and off with the modulator), Onset/offset-fringe (carrier gated on 250 ms before modulator onset and gated off 250 ms after modulator offset), Offset-fringe (carrier gated on with the modulator and gated off 250 ms after modulator offset), and Onset-fringe (carrier gated on 250 ms before modulator onset and gated off with the modulator). For the purposes of this study, the continuous carrier condition of Lee et al (2006) will be referred to as the onset/offset-fringe condition to make a clear distinction from the continuous carrier condition of Sheft and Yost (1990), where the wideband noise carrier was continuously on.…”