Laterality of auditory startle responses in humans

Is startle a lateralised response in early infancy?

The aim of the study was to explore whether the acoustic startle response shows signs of early lateralisation. Using non-invasive startle measurements (Automated Infant Motor Movement Startle Seat and Facial Action Coding System), an analysis of response latencies and intensities on the right and left body sides was performed, investigating the presence of asymmetries on the whole-body startle and on the facial component of the startle motor pattern in a group of 5-month-old infants. The findings suggest that the infant whole-body startle is a lateralised response, characterised by a right bias latency. This lateralisation could reflect an underlying lateralised organisation of the infant startle neural circuitry. On the other hand, the analysis of the facial component of the startle motor pattern did not reveal any significant asymmetry. The discrepancy found in the whole-body response and in the startle facial component will be discussed, reflecting on the limits of the adopted methodologies. The use of a high-speed camcorder might allow future research to analyse more in depth the startle fast face responses.

Considerations for the use of a startling acoustic stimulus in studies of motor preparation in humans

Recent studies have used a loud (> 120 dB) startle-eliciting acoustic stimulus as a probe to investigate early motor response preparation in humans. The use of a startle in these studies has provided insight into not only the neurophysiological substrates underlying motor preparation, but also into the behavioural response strategies associated with particular stimulus-response sets. However, as the use of startle as a probe for preparation is a relatively new technique, a standard protocol within the context of movement paradigms does not yet exist. Here we review the recent literature using startle as a probe during the preparation phase of movement tasks, with an emphasis on how the experimental parameters affect the results obtained. Additionally, an overview of the literature surrounding the startle stimulus parameters is provided, and factors affecting the startle response are considered. In particular, we provide a review of the factors that should be taken into consideration when using a startling stimulus in human research.