Effects of temporal uncertainty and temporal expectancy on infants' auditory sensitivity.

Adults are more sensitive to a sound if they know when the sound will occur. In the present experiment, the effects of temporal uncertainty and temporal expectancy on infants' and adults' detection of a 1 kHz tone in a broadband noise were examined. In one experiment, masked sensitivity was measured with an acoustic cue and without an acoustic cue to possible tone presentation times. Adults' sensitivity was greater for the cue than for the no-cue condition, while infants' sensitivity did not differ significantly between the cue and no-cue conditions. In a second experiment, the effect of temporal expectancy was investigated. The detection advantage for sounds occurring at an expected (most frequent) time, over sounds occurring at unexpected (less frequent) times, was examined. Both infants and adults detected a tone better when it occurred before or at an expected time following a cue than when it occurred at a later time. Thus, despite the fact that the auditory cue did not improve infants' sensitivity, it nonetheless provided the basis for temporal expectancies. Infants, like adults, are more sensitive to sounds that are consistent with temporal expectancy.