The effect of a cross-trial shift of auditory warning signals on the sequential foreperiod effect Michael B. Steinborn * , Bettina Rolke, Daniel Bratzke, Rolf Ulrich Cognitive and Biological Psychology, Psychologisches Institut, Universität Tübingen, Friedrichstrasse 21, 72072 Tübingen, Germany article info Article history: Received 8 October 2009 Received in revised form 28 December 2009 Accepted 31 December 2009 Available online 21 January 2010 PsycINFO classifications: 2330 2221 2340 2343 2346 Keywords: Sustained attention Variable foreperiod effect Classical conditioning Stimulus discrimination Alerting signal Ready signal abstract When a warning signal (WS) precedes an imperative signal (IS) by a certain amount of time (the forepe- riod, FP), responses are speeded. Moreover, this effect is modulated by the FP length in the previous trial. This sequential FP effect has lately been attributed to a trace-conditioning mechanism according to which individuals learn (and re-learn) temporal relationships between the WS and the IS. Recent evidence sug- gests that sensory WS attributes are critical to trigger time-related response activation. Specifically, when WS modality is shifted in subsequent trials (e.g., from auditory to visual modality), the sequential FP effect becomes attenuated. This study examined whether the sequential FP effect is reduced only by between-modality shifts or whether this attenuation generalizes to cross-trial shifts of WS attributes within modalities. We compared dimensional (low vs. high tone frequency) and qualitative shifts (pure tone vs. noise) of equal-intense auditory WS events. The results of four experiments revealed that shifts of tone frequency did not, whereas shifts of qualitative tone characteristics did attenuate the sequential FP effect. These results support the view that the WS acts as a trigger cue that unintentionally activates responses at previously reinforced critical moments. Ó 2010 Published by Elsevier B.V. 1. Introduction Warning signals (WS) preceding an imperative response signal (IS) are known to speed-up responses via both top-down guided (i.e., intentional) and bottom-up triggered (i.e., unintentional) pro- cesses (Hackley, 2009; Los & Schut, 2008). In a typical experiment, the IS follows the WS by a certain duration (referred to as forepe- riod, FP), enabling individuals to establish a state of nonspecific preparation at the moment of IS occurrence (referred to as the imperative moment). In a constant FP paradigm, the IS occurs reg- ularly on time after the WS and so individuals are enabled to syn- chronize peak readiness with the imperative moment. In a variable FP paradigm, the IS occurs irregularly after the WS and thus indi- viduals have little reliable information to time their preparation. Consequently, reaction times (RTs) to the IS are longer in the var- iable FP condition than in the constant FP condition. Moreover, in the variable FP condition, responses are usually slow in short FP trials but fast in long FP trials, yielding a downward-sloping FP- RT function (Niemi & Näätänen, 1981, pp. 137–141). This variable FP effect is usually interpreted such that the elapsing time after the WS contains information about IS occurrence, since the probability of IS occurrence increases as the FP interval becomes longer (Baumeister & Joubert, 1969; Karlin, 1959; Klemmer, 1957). From a strategic point-of-view, the WS event is considered a meaningful signal that reminds individuals to intentionally start preparation according to task rules and instructions (Gottsdanker, 1980; Näätänen & Merisalo, 1977). Notably, even when no explicit WS is given (as is the case in serial choice reaction time tasks), individuals may strategically use kinaesthetic feedback of their previous response as a warning to start preparation for the next IS (Rabbitt & Vyas, 1980). This strategic view implies that the indi- viduals engage in a rather abstract cognitive process of attaining preparation, using the WS event symbolically by means of rule-uti- lization (Bourne, 1966, pp. 19–21), that is without referencing to a particular WS exemplar or to specific sensory attributes of partic- ular exemplars. A further important assumption of this view is that individuals actively track the time flow after the WS and enhance preparation accordingly (Näätänen, 1971; Rabbitt & Vyas, 1980; Requin & Granjon, 1969). This process of monitoring the conditional probability of IS occurrence during the FP interval is considered an intentional process that requires the controlled 0001-6918/$ - see front matter Ó 2010 Published by Elsevier B.V. doi:10.1016/j.actpsy.2009.12.011 * Corresponding author. Tel.: +49 7071 29 74512; fax: +49 7071 29 2410. E-mail address: michael.steinborn@uni-tuebingen.de (M.B. Steinborn). Acta Psychologica 134 (2010) 94–104 Contents lists available at ScienceDirect Acta Psychologica journal homepage: www.elsevier.com/locate/actpsy