Listening to infant distress vocalizations enhances effortful motor performance.

There are few sounds that carry as much biological clout as the cries of a distressed infant. Consider a crying infant on a plane: the sound is as unpleasant as it is difficult to ignore, even amongst a host of other environmental noises. A distressed infant’s cry, characterized by high and variable pitch, elicits autonomic arousal in the listener as measured by heart rate, blood pressure, skin conductance [for review, see (1,2)] or hand grip force (3). The physiological arousal seen in response to infant cries may reflect a ‘high-alert’ state which prepares an adult to react rapidly to the infant’s distress (4). We examined whether the reported physiological change in response to infant cries translates into measurable differences in adults’ ability to move in a concerted and accurate manner. To this end, we played a series of infant cries and other sounds to a group of adults and measured subsequent performance on an effortful motor speed and dexterity task, in the form of a miniature version of the classic arcade game, ‘Whack-a-mole’. This game is brief but engaging and requires participants to press down on a target button (indicated by a light), with a predetermined amount of force, in order to score points. Within the same individuals, we compared performance on this task after listening to infant distress vocalizations, adult distress vocalizations and nondistressed, but high-pitched bird vocalizations. An individual’s overall score on the task reflected their success in pressing target buttons quickly enough and with sufficient force. An additional, subtle measure of change in performance was obtained in the form of effort exerted by participants, by measuring the pressure applied to target buttons during the game. Similar measures such as hand-grip force in humans (5) or lever pressing in animal models have been taken as an index of behavioural activation or motivation to act (6). Forty adults (20 men), ranging in age from 19 to 59 years took part (M = 26.5, SD = 8.2). Three participants were parents, but none had young children. All participants had normal hearing and normal vision or vision corrected to normal. The task, a small-scale version of ‘Whack-a-mole’ (Fig. 1A, ‘Whack it’, USB version), requires participants to press one of nine buttons, whose location varies randomly across the game. As the game progresses, the speed of change in location of the target button increases. The game was mounted on top of electronic scales (Salter 1036 BKDR), which were used to gauge the amount of effort participants exerted to push the buttons by measuring peak weight (in grams; minimum, maximum and average weights were recorded by videotaping the scales for the duration of the experiment). The amount of effort participants needed to apply to a target button in order to score was measured on the scales as approximately 350 g. After playing three 30 sec practice rounds, each participant listened to 4.5 min of one of the sound categories and then immediately replayed the game for 60 sec. This was repeated for each of the sound categories, with the order in which participants heard each sound category counterbalanced across participants. Each sound category consisted of 15 sounds, clipped to 1500 msec, free from background noise and matched to have linear rise and fall times of 150 msec and comparable average root mean square intensity. The sounds were presented at 70 dBFS above each participant’s absolute hearing threshold using Sony In-Ear earphones (MDR-EX77LP). The three categories of sound Acta Pædiatrica ISSN 0803–5253