Uni-, bi- and tri-modal warning signals: Effects of temporal parameters and sensory modality on perceived urgency Jan B.F. van Erp ⇑ , Alexander Toet, Joris B. Janssen TNO, Soesterberg, The Netherlands article info Article history: Received 9 October 2013 Received in revised form 23 June 2014 Accepted 30 July 2014 Keywords: Alerts Warning signals Multi-sensory Urgency Tactile Visual Auditory abstract Multi-sensory warnings can potentially enhance risk communication. Hereto we investigated how tem- poral signal parameters affect perceived urgency within and across modalities. In an experiment, 78 observers rated the perceived urgency of uni-, bi-, and/or tri-modal stimuli as function of 25 combina- tions of pulse duration (range 100–1600 ms) and inter pulse interval length (100–1600 ms). The results showed that perceived urgency increases with signal rate. Inter pulse interval showed a larger effect than pulse duration and the largest differences in perceived urgency as function of inter pulse interval occurred at the smallest pulse duration (100 ms). The effects of pulse duration and inter pulse interval were universal across modalities. Bi- and tri-modal signals were perceived as more urgent than each of their uni-modal constituents. We conclude that temporal parameters can be deployed to construct integrated, multi-sensory warning signals with a pre-specified degree of perceived urgency. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction In modern operating environments people are frequently con- fronted with warning signals presented in different sensory modal- ities. Warning signal optimisation requires a match between warning criticality and perceived warning urgency (operationally defined as the impression of urgency that a signal evokes in an observer). Although it is known that perceived signal urgency depends on effective multi-sensory integration, it is currently not known how the spatio-temporal characteristics of the individual signal channels contribute to the overall perceived signal urgency. Here we investigated the effects of pulse duration and inter pulse interval on the perceived urgency of uni-, bi- and tri-modal (audi- tory, visual and tactile) signals. 1.1. Toward multi-modal warning signals Operators working in information rich environments such as in medicine, aviation and road transport may suffer from an over- abundance of warning signals presented in different sensory modalities. For instance, a midsize car may already have several flashes, beeps and even buzzes in the driver’s seat linked to cruise control, collision avoidance, parking assistance, communication, and entertainment systems. Lack of integration of these signals may result in increased workload, distraction, and ultimately com- promise safety (Carsten and Nilsson, 2001; ECMT, 1995; Rumar, 1990). New display technologies in amongst others cars and aircraft provide excellent opportunities to integrate auditory, visual and more recently also tactile warning signals (e.g. vibrations pre- sented through a car seat, De Vries et al., 2009; Hogema et al., 2009). Potential advantages of multi-sensory warning signals are faster reactions (Bernstein et al., 1969; Diederich and Colonius, 2004; Hershenson, 1962) and reduced risk of sensory overload (Hancock et al., 2013; Lu et al., 2013; Ngo et al., 2012; Prewett et al., 2012; Spence, 2011). However, effective multi-sensory inte- gration requires spatio-temporal and semantic congruency across sensory modalities (Kolers and Brewster, 1985). At a perceptual level, multi-sensory integration is optimal when stimulation in dif- ferent sensory modalities occurs approximately at the same time and originates from the same location. In addition to perceptual congruency, signals should also be congruent semantically, includ- ing perceived urgency of warning signals. Currently, multi-sensory warning signals are being applied at an increasing scale, and improved knowledge on optimal integration is indispensable to make full use of their potential advantages. http://dx.doi.org/10.1016/j.ssci.2014.07.022 0925-7535/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Address: TNO Perceptual and Cognitive Systems, Kampweg 5, PO Box 23, 3769 ZG, The Netherlands. Tel.: +31 (0) 88 8665982; fax: +31 (0) 346353977. E-mail addresses: jan.vanerp@tno.nl (J.B.F. van Erp), lex.toet@tno.nl (A. Toet), joris.janssen@tno.nl (J.B. Janssen). Safety Science 72 (2015) 1–8 Contents lists available at ScienceDirect Safety Science journal homepage: www.elsevier.com/locate/ssci