Lateralized readiness potentials (LRPs) were used to determine the stage(s) of reaction time (RT) responsible for speed-accuracy trade-offs (SATs). Speeded decisions based on several types of information were examined in 3 experiments, involving, respectively, a line discrimination task, lexical decisions, and an Erikson flanker task. Three levels of SAT were obtained in each experiment by adjusting response deadlines with an adaptive tracking algorithm. Speed stress affected the duration of RT stages both before and after the start of the LRP in all experiments. The latter effect cannot be explained by guessing strategies, by variations in response force, or as an indirect consequence of the pre-LRP effect. Contrary to most models, it suggests that SAT can occur at a late postdecisional stage.

Stelmach, Herdman, and McNeil (1994) suggested recently that the perceived duration for attended stimuli is shorter than that for unattended ones. In contrast, the attenuation hypothesis (Thomas & Weaver, 1975) suggests the reverse relation between directed attention and perceived duration. We conducted six experiments to test the validity of the two contradictory hypotheses. In all the experiments, attention was directed to one oftwo possible stimulus sources. Experiments 1 and 2 employed stimulus durations from 70to 270msec. Astimulus appeared in either the visual or the auditory modality. Stimuli in the attended modality were rated as Ionger than stimuli in the unattended modality. Experiment 3 replicated this flnding using a different psychophysical procedure. Experiments 4-6 showed that the finding applies not only to stimuli from different sensory modalities but also to stimuli appearing at different locations within the visual field. The results of all six experiments support the assumption that directed attention prolongs the perceived duration of a stimulus.Since the influential monograph by James (1890), there has been agreement that attention plays an important role in the perception oftime (Brown & West, 1990). Specifically, subjects estimate an interval to be shorter when an additional task requires the processing of nontemporal information. For example, in the classical studies ofKatz (1906), intervals ofabout 1.2 sec werejudged shorterwhen attention was distracted by an accompanying task (e.g., reading ofsyllables). Meanwhile, numerous studies have replicated and extended this basic finding with various dual-task paradigms (Grondin & Macar, 1992;Hülser, 1924; Macar, Grondin, & Casini, 1994;Predebon, 1996;Quasebarth, 1924;Thomas & Cantor, 1978;Underwood & Swain, 1973;Zakay, 1993;Zakay & Tsal, 1989).For example, Macar et al. (1994) employedan attentionalsharing method. In each trial, several words appeared within an interval of 12 or 18 sec. The words came from different semantic categories and the subjects' task was to count animal names and to reproduce the duration of the word series at the end of the trial. Subjects were asked to divide their attention between the two tasks in prespecified proportions. When more attention was devoted to the counting task, subjects underestimated the duration of the word series. In a further experiment, the authors employed a discrimination task in which subjects were presented with stimuli of varying duration and intensity and judged both stimulus dimensions. As in the Parts of this paper were presented at the annual meetings of the International Society for Psychophysics, 1994 (Vancouver, Canada) and 1996 (Padua, Italy). We thank Hiltraut Müller-Gethmann for her comments on an earlier version ofthis article and Lloyd L. Avant, Jim Enns, and Ray Klein for their insightful reviews. Correspondence should be addressed to S. Mattes, General Psychology I, Fachbereich 3, University of'Wuppertal, Gauss-Strasse 20, D-42097 Wuppertal, Germany (email: mattes@uni-wupperta...

No abstract

Three experiments examined whether temporal uncertainty about the delivery of a response stimulus affects response force in a simple reaction time CRT) situation. All experiments manipulated the foreperiod; that is, the interval between a warning signal and the response stimulus. In the constant condition, foreperiod length was kept constant over a block of trials but changed from block to block In the variable condition, foreperiod length varied randomly from trial to trial. A visual warning and response stimulus were used in Experiment 1; response force decreased with foreperiod length in the variable condition, but increased in the constant condition. This result is consistent with the hypothesis that responses are less forceful when the temporal occurrence of the response stimulus is predictable. In a second experiment with an auditory warning signal and a response stimulus, response force was less sensitive to foreperiod manipulations. The third experiment manipulated both the modality and the intensity of the response signal and employed a tactile warning signal. This experiment indicated that neither the modality nor the intensity of the response signal affects the relation between response force and foreperiod length. An extension of Naatanen's (1971)motor-readiness model accounts for the main results.In a typical reaction time (RT) experiment, a warning signal precedes the imperative response stimulus.' Since the pioneering study of Woodrow (1914), it has been repeatedly documented that RT is strongly affected by the interval between the warning signal and the stimulus, that is, the foreperiod. According to Niemi and Naatanen (1981 ), the warning signal is used as a temporal reference for response preparation. Subjects estimate the point in time when the stimulus is delivered and try to synchronize response preparation with stimulus occurrence. Predictability ofthe stimulus and, hence, optimal response preparation depend on several foreperiod factors (for a review, see Niemi & Naatanen, 1981). A consistent finding is that factors favoring the exact prediction of the stimulus yield especially short RTs (e.g., constant foreperiods compared with variable ones). Some RT theorists (e.g., Sanders, 1990) assume that foreperiod manipulations affect the duration of motor processing, that is, the motoric portion ofRT.Given that foreperiod factors operate at a motoric level, one may ask whether these factors influence not only RT but also the exerted force in making the response. Recent studies (Giray, 1990;Jaskowski & Verleger, 1993) have tackled this question. Giray employed variable foreperiods in a simple RT task. Ineach trial, a foreperiod length was This work was supported by the Deutsche Forschungsgemeinschaft (UL 88/103). We appreciate the helpful comments of Hartmut Leuthold, Jeff Miller, and two anonymous reviewers. We are also indebted to Hiltraut Miiller-Gethmann for assistance in data collection and helpful comments on an earlier draft of this manuscript. Correspondence should be addressed to R. Ulric...

No abstract

T h ree exp erim en ts assessed th e h ypo th esis that im m ediate arou sal en h an ces resp on se force in speed ed reaction -tim e tasks. Im m e diate arou sal w as m an ipu lated via th e p h ysical ch ar acteristics of a w ar n ing signal th at closely p reced ed th e im p erative resp on se sign al. T he ® rst exp erim en t revealed th at re sp o nses were m ore forcefu l an d faste r for a lou d than for a so ft w ar n ing sign al. T h e seco nd exp erim en t m an ipulated th e d u ration of an au d itory w ar nin g sign al; m ore forcefu l bu t s low er resp on ses w ere obtained for lo n ger d u ration s of th e w ar nin g sign al. T he third exp erim ent em p loyed a visu al w ar n ing sign al, an d its inten sity w as eith er rath er w eak or m od er ate ly brigh t; m ore forcefu l resp on ses an d sligh tly faster resp on ses w ere obser ved for th e brigh te r w ar n ing signa l. A lthou gh th e resu lts of E xperim en t 1 an d 2 m ay ag ree w ith an arou sal acc ou n t, th e ® n d ings of E xp erim en t 3 argu e ag ainst su ch an accou nt. A stim ulu s± resp on se com p atibility hy p oth esis is su ggested as on e p ossible alter n ative accou nt.L ittle is know n about the effects of factors w ell-studied in reactio n tim e (RT ) research o n the dynam ics of the response itself, although response force (R F) is consid ered a``ubiquitous dep end ent variable' ' (L uce, 1986, p. 51). Som e recent chro nom etric studies have used RF as a variable supplem entary to RT (A bram s & Balota, 1991; A ngel, 1973; G iray, 1990 ). T hese au thors reported th at R F is in¯uenced by experimental factors that had been trad itionally assum ed to affect o nly early non-m o toric stages in the stim ulus± response processing chain . Fo r exam ple, A ngel (1973) reported that stim ulus in tensity in¯uences RF, although several au thors h ave attributed inten sity effects entirely to sensory processing or at least to no n-m otoric factors (cf. U lrich & Stapf, 1984). E ncou raged by the above studies, G iray an d U lrich (1 993) em ployed RF to assess the possibility of m otor coactivatio n (M iller, 1982) in a redundan t-signals task. O n u nim odal signal trials, either an au ditory or a visual signal w as presented alo ne; on redundan tsignals trials, b oth sign als w ere presented together. S ubjects w ere asked for a speeded response as soo n as they detected a visual or an au ditory signal. G iray an d U lrich observed not only faster but also m ore forceful respo nses on redundan t-signals trials, Requests for reprints should be sent to R olf U lric h, G ene ral Psyc holog y I, FB 3, U nive rsit y of Wuppertal, G auss-Strass e 20, D ± 420 97 Wuppertal, G er m any. Em ail: ulric h@ w rcs1.ur z.uni-w uppertal.de This work w as supported by the Deutsche Forschungsgemeinsch a ft (U L 88/103). We thank Rita L eydel for ru nning the e xp erim ents an d ap preciat e the helpful com me nts of H artmu t Le uthold, Je ff M iller, and tw o an onymo us reviewe rs. q 199 6 The E xp erim ental Psyc holo g y S ociety

Three experiments assessed the hypothesis that immediate arousal enhances response force in speeded reaction-time tasks. Immediate arousal was manipulated via the physical characteristics of a warning signal that closely preceded the imperative response signal. The first experiment revealed that responses were more forceful and faster for a loud than for a soft warning signal. The second experiment manipulated the duration of an auditory warning signal; more forceful but slower responses were obtained for longer durations of the warning signal. The third experiment employed a visual warning signal, and its intensity was either rather weak or moderately bright; more forceful responses and slightly faster responses were observed for the brighter warning signal. Although the results of Experiment 1 and 2 may agree with an arousal account, the findings of Experiment 3 argue against such an account. A stimulus-response compatibility hypothesis is suggested as one possible alternative account.

No abstract