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

This study describes how an auditory looming technique was used to investig ate 4-to 6-month-old infants' sensitivity to sound pressure level (SPL) as an auditory distance cue. Thirty-two infants were tested in complete darkne ss and presented with auditory stimuli that underwent unidirectional variat ions in SPL (40-70dB). The rate at which SPL was varied during the course o f trials (past vs. slow) was manipulated by varying trial length (5s vs. 10 s). During stimulus presentation, measures were taken of the amount of back ward body pressure infants exerted in response to increasing SPL trials (i. e. illusory approach) compared to decreasing SPL trials (i.e. illusory rece de). Analysis of the pattern of backward body movements made during the cou rse of experimental trials support the argument that infants responded to t he directionally specific spatial information afforded by changing SPL. Avo idance behaviour was associated with SPL increase but not SPL decrease cond itions. 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 in fants detect information for changing object distance primarily on the basi s of SPL variation.