Localization of Temporal Preparation Effects Via Trisected Reaction Time

Psychophysiology, 44 (2007), 334–338. Blackwell Publishing Inc. Printed in the USA. Copyright r 2007 Society for Psychophysiological Research DOI: 10.1111/j.1469-8986.2007.00500.x

BRIEF REPORT Localization of temporal preparation effects via trisected reaction time

STEVEN A. HACKLEY,a ANDREA SCHANKIN,b ANDREAS WOHLSCHLAEGER,b and EDMUND WASCHERc aDepartment of Psychological Sciences, University of Missouri, Columbia, Columbia, Missouri, USA bMax Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany cLeibniz Institute for Working Environment and Human Factors, Dortmund, Germany

Abstract Previous research using nonchronometric measures in humans and animals has shown that warning signals can influence stages of processing throughout the reaction time (RT) interval. However, latency measures indicate that warning effects on RT are not due to the speeding of motor processes, at least not late ones. To better isolate the chronometric effects of temporal preparation, we used lateralized event-related potentials to divide mean RT into three time segments. Foreperiod duration had only a small, nonsignificant influence on the first and last segments (early visual and late motor processes, respectively). The chronometric effect was mainly restricted to the middle interval, which extended from onset of the N2pc component to onset of the lateralized readiness potential. The results imply that temporal preparation primarily speeds late perception, response selection or early motor processes. Descriptors: Mental chronometry, Reaction time, Event-related potential, Attention, Vision

Efforts to determine the first point in time at which overlayed dramatically across conditions (for review, see Correa, Lupiań˜ez, waveforms for potentials evoked by attended and unattended Madrid & Tudela, 2006). stimuli differ has played an important role in our understanding Considering the difficulty of comparing evoked potentials of selection based on stimulus attributes such as location, pitch, that ride upon a rapidly shifting baseline, it is not surprising that and color (Hillyard, Hink, Schwent & Picton, 1973; Mangun, the results from previous studies of temporal attention have 1995). For example, the fact that effects of spatial attention on been inconsistent (Correa et al., 2006). Subtraction components event-related potentials (ERPs) can occur as early as about 15 ms should be relatively immune to shifting baselines and to con- for audition and 90 ms for vision argues against the late selection tamination by extraneous sources. The only study of temporal view that perceptual analysis is fully automatic (for review, see attention effects to date that examined a subtraction component Hackley, 1993). failed to observe any effects (Rudell & Hu, 2001, studying the Unfortunately, this approach is unlikely to work in the case of lexical ‘‘Recognition Potential’’). temporal attention. For one thing, the effects of selectively at- Here we take a different approach toward chronometrically tending to a particular point in time appear to lie mainly within localizing the effects of temporal attention. We measured the decision and motor processes (Coull & Nobre, 1998; Hackley & onset of two subtraction components, one perceptual and one Valle-Inclań, 2003), processes that are not assessed by modality- motor, that were extracted from the ERP. Specifically, we re- specific evoked potentials. Another problem is that it is difficult corded the N2pc (pc 5 posterior, contralateral relative to a visual to precisely identify the onset of warning effects for potentials target) and the lateralized readiness potential (LRP). The onsets evoked by the imperative stimulus in a warned reaction time of these components were then used as landmarks to partition (RT) task because these components are superimposed on the mean RT into three time segments. Our goal was to determine offset of the contingent negative variation (CNV), which varies which of these three segments is shortened by temporal preparation. This methodology was independently developed by Ruge, Stoet, and Naumann (2006), who used it to chronometrically localize the effects of a task switching set. This research was supported by sabbatical grants to the first author Unlike some ERP components, the N2pc and LRP have well- from the Max Planck Institute for Human Cognitive and Brain Sciences defined cognitive and neuroanatomical correlates. The N2pc and Tuebingen University. occurs at around the time of the second major negative deflection Address reprint requests to: Steven A. Hackley, Department of Psy- chological Sciences, 210 McAlester Hall, University of Missouri, Col- in the visual evoked potential, with maximum amplitude at a umbia, Columbia, MO 65211, USA. E-mail: [email protected]. posterior site (PO7/8) contralateral to the hemifield containing 334 Localization of temporal preparation effects 335 the target in a visual search task (Luck & Hillyard, 1994; Procedure Wascher, 2005). Hence, occurrence of the N2pc indicates that the Recent work on temporal attention has been dominated by a participant has perceptually analyzed the display sufficiently to methodology in which a precue on each trial either validly or determine the side of the display in which the target lies. Dipole invalidly predicts the imperative’s time of arrival (e.g., Coull & modeling studies suggest a single generator for the N2pc, one Nobre, 1998). Although precue manipulation studies have led to that lies within lateral extrastriate cortex (Hopf, Boelmans, Sch- many valuable insights, we chose instead a traditional fore- oenfeld, Luck, & Heinze, 2004). The time interval extending period-duration manipulation. This allows continuity with the from stimulus onset until N2pc onsetFa dependent measure in 125-year-old literature on warning effects (which began with the present studyFis known to be sensitive to target salience or Wundt, 1880, described in James, 1890) and permits comparison discriminability and number of distractors (Wascher & Wausch- with similar conditioning, CNV, and reflex modulation studies kuhn, 1996; Wolber & Wascher, 2005). (Hackley & Valle-Inclań, 2003). The LRP is a surface-negative waveform with maximum am- In the present study, there were two blocks of 260 trials in plitude over motor cortex. It is extracted from the ERP by sub- which a short, easy-to-estimate interval of 600 ms separated the tracting potentials recorded at the electrode ipsilateral to the onset of the warning and imperative stimuli. During the other planned response from those recorded at the corresponding two balanced blocks of trials, a longer and hence more difficult- contraleral electrode. Occurrence of the LRP indicates that the to-estimate interval was used, 3000 ms. The imperative for the participant has chosen which hand to respond with. Dipole choice RT task was the Roman letter ‘‘A’’ or ‘‘B’’ (0.5 0.61 in modeling studies indicate that the primary generator lies within size), randomly presented 1.11 to the left or right of fixation. As the hand area of M1, with additional contributions from nearby in some previous N2pc studies at this laboratory (Wascher & premotor and somatosensory cortices (Boetzl, Plendl, Paulus, & Wauschkuhn, 1996) the distractor consisted of three horizontal Scherg, 1993). The time interval extending from LRP to response lines, similar to the Greek letter X, presented at the mirror-image onset is known to be sensitive to response probability, response location of the opposite hemifield. complexity, and key press force (Masaki, Wild-Wall, Sangals, & With only a single distractor and target, this is certainly an Sommer, 2004; Mueller-Gethmann, Rinkenaur, Stahl, & Ulrich, austere search task. However, the paradigm yields N2pc com- 2000; Smulders, Kok, Kenemans, & Bashore, 1995). ponents that are similar in morphology, amplitude, latency, top- Although trisection of the RT interval has not previously been ography, and functional correlates to the N2pc waveforms employed to study temporal preparation, seven previous experi- obtained with more complex tasks (Wascher & Wauschkuhn, ments partitioned mean RT based on LRP onset (Hackley & 1996). Valle-Inclań, 1998, 1999; Mueller-Gethmann, Ulrich, & Rin- The warning signal in our study was a 400-ms vibration de- kenaur, 2003, Experiments 1 and 2; Smulders et al., 1995; Tan- livered simultaneously to the left and right ankles. The task was donnet, Burle, Vidal, & Hasbroucq, 2003, 2006; for review, see to press the upper key with the thumb of the right hand when they Hackley & Valle-Inclań, 2003). Using a variety of methods to saw an ‘‘A’’ or the lower key with the left thumb when they saw a manipulate temporal preparation, six of these studies yielded ‘‘B.’’ As expected, RTs were slower in the 3000- than in the 600- consistent evidence that this form of attention has no effect on the ms condition (M difference 5 83 ms, SD 5 43, z[31] 5 56.5, duration of the LRP-to-response (LRP-R) interval. The seventh po.001; RT for the 600-ms condition averaged 475 ms, SD 5 89 study did obtain a foreperiod effect on the LRP-R interval, but ms). This difference was not due to a speed–accuracy trade-off the effect was small and its variation as a function of foreperiod because errors were more common in the long- than in the short- duration differed from that of RT (Mueller-Gethmann et al., foreperiod condition (M 5 0.030 and 0.023, respectively, 2003, Experiment 1). Converging evidence for the absence of z[31] 5 14.49, po.001. temporal preparation effects on the duration of late motor pro- As described in the introduction, the goal of our psycho- cesses has recently been obtained using a wholly unrelated meth- physiological analysis was to partition this serviceably large be- od, the psychological refractory period paradigm (Bausenhart, havioral effectF83 msFinto three time segments that roughly Rolke, Hackley, & Ulrich, 2006). correspond to early perception, decision, and late motor stages. Based on these findings, we predict that the LRP-R interval The sizable behavioral effect (83 ms), sample size (31 partici- will not be modulated by foreperiod duration. The best existing pants), and number of trials per condition (520) would be ex- data regarding early visual processing, that of Rudell and pected to yield stable parameter estimates and a considerable Hu (2001), suggest that null effects are also likely for the first of power to reject the null hypothesis. In addition, a follow-up study the three time segments. The main chronometric effect of forer- (N 5 12) was conducted to confirm all visual ERP results. The period duration, therefore, is predicted to lie within the middle methods were identical except that subjects responded using two interval. fingers of the same hand, which precluded chronometric LRP analyses. Behavioral results were similar, with a 71-ms difference in RTs across conditions, F(1,12) 5 52.75, po.001, and a higher error rate for the long-foreperiod condition (M 5 0.037 Methods and 0.021 for the 3000- and 600-ms foreperiods, respectively; Wilcoxon’s T 5 6.0, po.005). Participants Thirty-one paid volunteers (6 men, 25 women; all right-handed; Recordings and Analyses age 20–31, M 5 25.5 years) constituted the final sample. The Surface electroencephalograms (EEG) and electrooculograms data from an additional participant (male) were rejected from the (EOG) were recorded using 64 Ag-AgCl electrodes embedded in psychophysiological analyses because he did not exhibit a meas- an elastic cap. The recording bandpass was DC to 200 Hz, with a urable LRP. Nearly all subjects had participated in previous vis- 50-Hz notch filter, a digitization rate of 500 Hz, and off-line low- uomotor experiments at this laboratory. pass filtration at 8 Hz. The 8-Hz cutoff was designed to yield a 336 S.A. Hackley et al. smooth leading edge, thereby enhancing the measurement of onset latency. Ocular artifacts were corrected via a standard subtraction procedure (Gratton, Coles, & Donchin, 1983). Trials with other artifacts (e.g., motion artifacts, amplifier saturation) were removed prior to signal averaging. The N2pc was largest at the PO7/8 electrode sites and the LRP at FC3/4. Only data from these electrode pairs are reported, but findings were similar at nearby sites, and the scalp topographies were comparable to those of previous N2pc and LRP studies. Lateralization components were extracted for each participant using the standard, double-subtraction method that gives these measures their well-known invulnerability to volume-conducted contamination from extraneous sources. Specifically, the N2pc was calculated by first subtracting the signal-averaged waveform at PO7 from that at PO8, and then subtracting the resulting average for trials with right-hemifield targets from those with left-hemifield targets. Similarly, LRP was computed by Figure 1. Grand average difference waves portraying N2pc (second subtracting FC3 from FC4, and then left-hand response trials negative peak; posterior, contralateral) at parieto-occipital electrode sites (PO7/8) as a function of short (600 ms) and long (3000 ms) foreperiods. from right-hand trials. Note that the N2pc and LRP were computed across orthogonal sets of trials, in that the hand responding and 1.1 mV, t[11] 5 2.6 and 2.7, pso.05; P3 amplitude difference at to the letter was independent of target hemifield. Consequently, the P3 electrode, M 5 2.3, t[11] 5 3.0, po.02). As noted earlier, the N2pc and LRP should be minimally vulnerable to contam- presubtraction evoked potentials are not as trustworthy as later- ination from one another. alization components because they are superimposed on the offset The effects of foreperiod on onset latencies measured at 50% of the CNV and, in the case of P3, sensorimotor cortex potentials of peak amplitude were assessed using jackknife t tests on the associated with the key-press response. grand average waveforms (Ulrich & Miller, 2001). Similar results Consistent with extensive prior research cited in the intro- were obtained with other methods, including regression-based duction, the LRP-R interval was not affected reliably by tem- estimates of absolute onsets for individual subjects and condi- poral attention, Fc(1,30) 5 1.252, p 5 .272; M 5 111 ms, tions. Supplementary evidence regarding the locus of foreperiod 600 M3000 5 122 ms, SD 5 38.5. Figure 3B shows the response- effects was obtained by measuring the peak latencies of N1 and locked averages for LRP, in which zero on the X axis indicates P3 from the presubtraction ERP waveforms. key-press onset. In contrast, the time from letter onset until stimulus-locked LRP onset was significantly reduced in the short foreperiod condition, Fc(1,30) 5 77.021, po.001 (Figure 3A, in Results which the origin of the X axis indicates stimulus onset). Based on N2pc and stimulus-locked LRP measurements, the middle time The three time intervals were estimated by (1) the onset latency of interval is estimated at 104 and 160 ms (SD 5 49), respectively, the N2pc, (2) the onset latency of the stimulus-locked LRP minus for the short- and long-foreperiod conditions. that of the N2pc, and (3) the response-locked LRP-to-key-press interval. As shown in Figure 1, the interval from stimulus onset until N2pc onset was not affected by foreperiod duration, Discussion Fc(1,30) 5 0.077, p 5 .783; M600 5 205 ms, M3000 5 209 ms, SD 5 24.5, (these time measurements are based on individual The principal contribution of the present study was to show that subject’s waveforms rather than the grand average). A small ef- the effect of temporal attention on RT lies mainly within an fect can be seen for the peak latency, but this difference did not approach significance. The larger amplitude in the short-foreperiod condition was statistically significant, t(30) 5 2.494, po.02. Null effects for latency were replicated in the follow-up study. The N2pc waveforms in that study (not shown) over- lapped perfectly until 180 ms, or 53% of peak amplitude (mean difference at 50% of peak 5 1.6 ms, SEM 5 9.8). There was no difference in N2pc amplitudes across conditions. Measurements of the N1 visual evoked potential were suggest- ive of an effect of foreperiod duration on perceptual analyses. N1 latency appeared to be shorter in the 600-ms condition by about 8 ms, t(30) 5 3.925 and 3.234 at O1 and O2, respectively, pso.005; seeFigure2.Base-to-peakamplitudesalsoappearedtobelargerin that condition, t(30) 5 1.977 and 2.098 at O1 and O2, pso.06 and .05. The P3 was larger following long foreperiods but faster following short foreperiods, t(30) 5 6.262 and 4.354, respectively, pso.001. Each of these effects was replicated in the follow-up study Figure 2. Grand average, presubtraction event-related potentials at the (N1 latency difference at O1 and O2, respectively, M 5 9and6ms, O2 electrode showing the effect of foreperiod duration on the N1 and P3 t[11] 5 3.0 and 2.4, pso.05; N1 amplitude differences, M 5 0.9 deflections. Localization of temporal preparation effects 337

exert some sort of influence on early perceptual and late motor processes. Visual psychophysics research has shown that temporal attention enhances d0, a relatively pure measure of perceptual sensitivity (e.g., Rolke & Hoffman, in press). Electrophysiological and neuroimaging data are congruent. An amplitude effect on at least one modality-specific ERP was obtained in five of the seven studies reviewed by Correa, Lupiań˜ez, and Tudela (2005). Both positron emission tomography and functional magnetic resonance imaging have documented temporal attention effects within visual cortical areas (e.g., Coull & Nobre, 1998). Effects of temporal attention on nonchronometric measures of late motor processes are also well established. Measures have included regional hemodynamic activity (e.g., Coull & Nobre, 1998), spinal reflexes (e.g., Scheirs & Brunia, 1985), trans- cranial magnetic pulse stimulation (Hasbroucq et al., 1999), response force (Ulrich & Mattes, 1996), and Laplacian amplitudes of unilateral motor cortex potentials (Tandonnet et al., 2003, 2006). In contrast to amplitude measures, findings for latency measures of visual and late motor processes have been inconsistent and of small magnitude. Only one of the seven studies reviewed by Correa and colleagues (2006) obtained a latency effect for an early, modality-specific evoked potential (P1 in this case). Simi- larly, only one of the seven LRP experiments concerning warning effects found an effect on the LRP-R interval (Mueller-Geth- mann et al., 2000, Experiment 1) and, as noted earlier, this modulation was not systematically related to the foreperiod-duration effect on RT. Tandonnet and colleagues (2003, 2006) have reported that foreperiod duration influences the response-locked onset of unilateral motor cortex potentials. However, the effect Figure 3. A: Stimulus-locked lateralized readiness potentials (sLRP) at size was small in both studies (13 and 4 ms, as noted above) and, fronto-central electrode sites (FC3/4) averaged across 31 participants, as judging from the published waveforms, might be specific to the a function of short and long foreperiods (600 and 3000 ms, respectively). particular measurement algorithm they employed. In stimulus-locked averaging, the EEG is segmented with respect to Because the visual system is highly parallel, a potential criti- stimulus onset; hence, the origin of the abscissa indicates stimulus onset. cism of our study is that the N2pc might reflect activity within a B: Grand average, response-locked, lateralized readiness potentials pathway that does not determine RT. For example, the N2pc (LRPr) overlying frontocentral cortex (FC3/4) as a function of short might solely index a process within the dorsal, action-based vis- and long foreperiod (600 and 3000 ms, respectively). In response-locked waveforms, zero on the X axis indicates response onset. ual stream, whereas temporal preparation might influence the speed of processing within the ventral, object-recognition visual stream. However, N2pc latency has been found to correlate intermediate time segment. To be precise, 67% of the 83-ms RT highly with RT in a number of studies (e.g., Wolber & Wascher, effect (i.e., 56 ms; 95% confidence interval 5 45–79 ms) could be 2005). Furthermore, the subtraction component studied by accounted for by modulation of the narrow time window ex- Rudell and Hu (2001), the lexical recognition potential, almost tending from the onset of N2pc at about 200 ms until onset of the certainly originates in the ventral stream. The presence versus LRP at about 350 ms. Numerically, the first and third segments absence of a warning signal exerted no effect whatsoever on the accounted for only 4 and 11 ms of the RT effect, respectively amplitude, latency, or morphology of that component. (95% confidence intervals: 16–7 ms for the first segment and Given that the locus of chronometric effects lies mainly within 1–21 ms for the second). the middle time segment (about 200–350 ms after stimulus on- Note that these estimates are not expected to exactly sum to set), what are the likely cognitive correlates? We know that this the RT effect (4156111 5 71, not 83 ms) due to differences in time interval extends from the point at which subjects have de- component morphology, thresholding between stages, and termined which side the target is on (N2pc) until the point at choice of measurement algorithm. The small size of the N2pc which they have chosen which hand to respond with (LRP). latency effect (4 ms at 50% of peak amplitude) is consistent with Logically, this interval could include late perceptual analyses, the apparent modulation of N1 peak latency (8 ms). Similarly, response selection, and early motor processes. Neuroimaging the small, nonsignificant effect on the LRP-R interval (10 ms at studies may help to resolve this question (e.g., Hackley et al., 50% of peak amplitude) is comparable to the magnitude of the 2007). effect reported by Tandonnet and colleagues for unilateral motor The trisection approach employed in this study was inde- cortex potentials (13 ms and 4 ms in their 2003 and 2006 studies, pendently developed by Naumann’s group (Ruge et al., 2006) respectively). and is an extension of the bisection method of Osman and Moore Although the trisection analysis generated null effects for the (1993). This new approach to mental chronometry has much to first and third segments, it is indisputable that warning signals recommend it. In comparison to the methods of Donders (1868/ 338 S.A. Hackley et al.

1969) and Sternberg (1969), the trisection method has fewer and McCarthy and Donchin’s (1981) method. We believe that the more plausible assumptions. The cognitive and neurophysiolog- trisection method merits consideration for application to a broad ical correlates of its measures are better deﬁned than are those of array of problems in cognitive science.

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