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

Abstract

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, both 5- 6 years and adults exhibited similar levels of temporal integration, while 7-8 and 10- 11 years showed less integration. This is because at both rates: (i) the youngest group (5-6 years) displayed the worst thresholds with 2 AM cycles but similar thresholds with 8 cycles compared to older children groups, and (ii) adults showed the best thresholds with 8 AM cycles but similar thresholds with 2 cycles compared to older children groups. 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.