Studies in infant behavioural audiometry. I. Neonates.

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The behaviour of 93 clinically normal neonates was video-recorded while they were presented with sequences of sound stimuli which varied in sound pressure level, bandwidth and rise time and which included two voice signals and a no-sound (control) trial. Video records were made both for the whole body aspect and for a 3 1/2 X "close-up" of the head. Later, the video records were shown to 6 observers who were allowed to see the babies for 10 sec at each trial. The first 5 sec was a pre-stimulus observation period, and the second 5 sec usually contained a sound stimulus. Between the trials, the observers were given 20 sec in which to record (1) pre-stimulus activity, (2) confidence in response, and (3) movement details (data for (3) not reported here). For the whole-body aspect, observers were allowed to see (1) the whole body, (2) the head, arms and trunk, (3) the arms, trunk and legs, (4) the head only, (5) the arms and trunk only, or (6) the legs only, during different viewing sessions. For the head aspect, they could see (7) the whole head, (8) the head above the upper lip, or (9) the head below the upper lip. This segmentation was achieved by masking parts of the television screen with shutters. The response confidence ratings were analysed using aspects of signal detection theory to show differences amongst various body segments (p less than 0.001), sound pressure levels (p less than 0.001), bandwidths (p less than 0.001), and rise times (p less than 0.01). There were significant interactions between sound pressure level X bandwidth (p less than 0.001), sound pressure level X rise time (p less than 0.01), and bandwidth X rise time (p less than 0.001). A 90-dB broad-spectrum noiseband was by far the most effective stimulus. The response to different sound stimuli was differentially affected by pre-stimulus activity state. The results are discussed in relation to recent work on clinical screening techniques.