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

Temporal integration for amplitude modulation in childhood: Interaction between internal noise and memory

It is still unclear whether the gradual improvement in amplitude-modulation (AM) sensitivity typically found in children up to 10 years of age reflects an improvement in "processing efficiency" (the central ability to use information extracted by sensory mechanisms). This hypothesis was tested by evaluating temporal integration for AM, a capacity relying on memory and decision factors. This was achieved by measuring the effect of increasing the number of AM cycles (2 vs 8) on AM-detection thresholds for three groups of children aged from 5 to 11 years and a group of young adults. AM-detection thresholds were measured using a forced-choice procedure and sinusoidal AM (4 or 32 Hz rate) applied to a 1024-Hz pure-tone carrier. All age groups demonstrated temporal integration for AM at both rates; that is, significant improvements in AM sensitivity with a higher number of AM cycles. However, an effect of age is observed as both 5-6 year olds and adults exhibited more temporal integration compared to 7-8 and 10-11 year olds at both rates. This difference is due to: (i) the 5-6 year olds displaying the worst thresholds with 2 AM cycles, but similar thresholds with 8 cycles compared to the 7-8 and 10-11 year olds, and, (ii) adults showing the best thresholds with 8 AM cycles but similar thresholds with 2 cycles compared to the 7-8 and 10-11 year olds. Computational modelling indicated that higher levels of internal noise combined with poorer short-term memory capacities in children accounted for the developmental trends. Improvement in processing efficiency may therefore account for the development of AM detection in childhood. This article is part of the Special Issue Outer hair cell Edited by Joseph Santos-Sacchi and Kumar Navaratnam.

The effect of frequency cueing on the perceptual segregation of simultaneous tones: Bottom-up and top-down contributions

Listeners were presented with two simultaneous tones of different frequencies (more than one octave apart) and asked to identify the tone that was amplitude-modulated while a tonal precursor was presented to cue the frequency of the lower frequency tone. Performance thresholds were estimated based on the duration of the tone-pair. In Exp. I the duration of the precursor varied from 100 to 400 ms and the inter-stimulus interval (ISI) between the precursor and the tone-pair varied from 0 to 1 s. The presence of the precursor facilitated segregation. As the ISI increased, the facilitation effect of the precursor increased for the precursor durations of 100 and 200 ms, but not for the 400-ms precursor duration. When the precursor was presented to the contralateral ear relative to the tone-pair in Exp. II, no significant change to the precursor effect was observed. These observations contradict the predictions of the model based solely on bottom-up processing, suggesting the likely involvement of top-down processes.