Use of an auditory looming task to test infants' sensitivity to sound pressure level as an auditory distance cue

Abstract

This study describes how an auditory looming technique was used to investigate 4-to 6-month-old infants’ sensitivity to sound pressure level (SPL) as an auditory distance cue. Thirty-two infants were tested in complete darkness and presented with auditory stimuli that underwent unidirectional variations in SPL (40–70dB). The rate at which SPL was varied during the course of trials (past vs. slow) was manipulated by varying trial length (5s vs. 10s). During stimulus presentation, measures were taken of the amount of backward body pressure infants exerted in response to increasing SPL trials (i.e. illusory approach) compared to decreasing SPL trials (i.e. illusory recede). Analysis of the pattern of backward body movements made during the course of experimental trials support the argument that infants responded to the directionally specific spatial information afforded by changing SPL. Avoidance behaviour was associated with SPL increase but not SPL decrease conditions. However, within the SPL increase condition infants engaged in more defensive leaning back in fast change trials compared to slow change trials. The overall pattern of results indicates that under certain conditions infants detect information for changing object distance primarily on the basis of SPL variation.