Temporal regularity effects on pre-attentive and attentive processing of deviance.

Abstract

Temporal regularity allows predicting the temporal locus of future information thereby potentially facilitating cognitive processing. We applied event-related brain potentials (ERPs) to investigate how temporal regularity impacts pre-attentive and attentive processing of deviance in the auditory modality. Participants listened to sequences of sinusoidal tones differing exclusively in pitch. The inter-stimulus interval (ISI) in these sequences was manipulated to convey either isochronous or random temporal structure. In the pre-attentive session, deviance processing was unaffected by the regularity manipulation as evidenced in three event-related-potentials (ERPs): mismatch negativity (MMN), P3a, and reorienting negativity (RON). In the attentive session, the P3b was smaller for deviant tones embedded in irregular temporal structure, while the N2b component remained unaffected. These findings confirm that temporal regularity can reinforce cognitive mechanisms associated with the attentive processing of deviance. Furthermore, they provide evidence for the dynamic allocation of attention in time and dissociable pre-attentive and attention-dependent temporal processing mechanisms.

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Biological Psychology 87 (2011) 146–151
Contents lists available at ScienceDirect
Biological Psychology
journal homepage: www.elsevier.com/locate/biopsycho
Temporal regularity effects on pre-attentive and attentive processing of deviance
Michael Schwartzea,∗, Kathrin Rothermicha, Maren Schmidt-Kassowb, Sonja A. Kotza
aMax Planck Institute for Human Cognitive and Brain Sciences, Independent Research Group “Neurocognition of Rhythm in Communication”, Stephanstrasse 1a, 04103 Leipzig,
Germany
bInstitute for Medical Psychology, Johann Wolfgang Goethe-Universität, Heinrich-Hoffmann-Strasse 10, 60528 Frankfurt am Main, Germany
a r t i c l ei n f o
Article history:
Received 4 October 2010
Accepted 27 February 2011
Available online 5 March 2011
Keywords:
ERP
Oddball
Attention
Timing
Regularity
a b s t r a c t
Temporal regularity allows predicting the temporal locus of future information thereby potentially
facilitating cognitive processing. We applied event-related brain potentials (ERPs) to investigate how
temporal regularity impacts pre-attentive and attentive processing of deviance in the auditory modality.
Participants listened to sequences of sinusoidal tones differing exclusively in pitch. The inter-stimulus
interval (ISI) in these sequences was manipulated to convey either isochronous or random temporal
structure. In the pre-attentive session, deviance processing was unaffected by the regularity manip-
ulation as evidenced in three event-related-potentials (ERPs): mismatch negativity (MMN), P3a, and
reorienting negativity (RON). In the attentive session, the P3b was smaller for deviant tones embedded
in irregular temporal structure, while the N2b component remained unaffected. These findings confirm
that temporal regularity can reinforce cognitive mechanisms associated with the attentive processing
of deviance. Furthermore, they provide evidence for the dynamic allocation of attention in time and
dissociable pre-attentive and attention-dependent temporal processing mechanisms.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
Continuous change is a fundamental characteristic of life.
Changes generate temporal structure or events in time, with effec-
tive behavior depending in part on the temporal coherence of
cognition, action, and these events. The key to temporal coherence
is adequate timing, i.e., the ability to be in the right place at the
right time. Timing and temporal organization are not only crucial
in overt behavior but also in cognitive processes and the alloca-
tion of cognitive resources (Fuster, 2001). How do neurocognitive
processes cope with the temporal structure of the environment to
achieve adequate timing in cognition and action? Adequate tim-
ing implies some internal representation of temporal structure. It
is unclear though whether temporal structure is processed implic-
itly, or whether an explicit representation of temporal structure is
generatedbydedicatedtemporalprocessingsystems(Buonomano,
2007; Ivry and Schlerf, 2008). Some neurofunctional models sug-
gest that dedicated temporal processing is a function of classical
motorsystemsofwhichthecerebellumisinvolvedinpre-attentive,
short-range,event-basedtemporalprocessing,whilethebasalgan-
glia engage in attention-dependent, longer-range, interval-based
temporal processing (Ivry, 1996; Lewis and Miall, 2003; Spencer
et al., 2003; Buhusi and Meck, 2005). A benefit that may arise from
∗Corresponding author. Tel.: +49 341 99402473; fax: +49 341 99402260.
E-mail address: schwartze@cbs.mpg.de (M. Schwartze).
the explicit processing and the evaluation of temporal structure is
to recognize and prospectively use temporal regularity. This would
allow to predict the temporal locus of future events and to allocate
attention towards important aspects of information. Expectations
and prior knowledge about upcoming information should entail
optimized timing in cognition and action even if the use of tem-
poral structure is subconscious and unintentional, i.e., if temporal
processing is exogeneous (Nobre et al., 2007; Coull and Nobre,
2008).
The proposed dissociation of pre-attentive and attention-
dependent temporal processing systems offers a starting point
to further characterize the underlying processes. In this context,
importantissuesconcern(1)themomentatwhichattentionaffects
temporal processing, (2) whether temporal structure can be pro-
cessed without adopting strategies for estimating time (Grondin,
2001), and (3) how attention is allocated and maintained in the
presence of acoustic, and hence inherently temporal, signals. Early
on, Bolton (1894) emphasized that attention appears discontinu-
ous and intermittent, and that it manifests in a wave-like form or
a series of pulses. Consequently, some form of adaptation deems
necessary to align the internal fluctuation of the attentional focus
with the temporal structure of external events. With respect to
the auditory domain, one important aspect in this interplay could
be the bias of the auditory system to search for regularities in
sensory input (Winkler et al., 2009). Although continuously chang-
ing, the temporal structure of the environment is not arbitrary.
Any perceived regularity in temporal structure can indicate a pat-
0301-0511/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.biopsycho.2011.02.021

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M. Schwartze et al. / Biological Psychology 87 (2011) 146–151
147
tern. Temporal patterns emerge in both the environment and in
the allocation of attention (Jones and Boltz, 1989). This transient
temporalstabilityincombinationwithpredictiveprocessingisfun-
damental for optimal anticipatory timing in cognition and action.
This notion is expressed in Dynamic Attending Theory (DAT; Jones
and Boltz, 1989; Large and Jones, 1999). DAT proposes that inter-
nal attending rhythms synchronize with external event structure.
This mechanism may be relevant to dissociate pre-attentive from
attention-dependent temporal processing mechanisms. Ongoing
processing of relatively stable temporal relations instantiates a
repetitive process which can be conceived as an instance of oscilla-
toryactivity.Oscillatoryactivityandinteractionsbetweendifferent
oscillations caused by appropriate external or internal stimula-
tion constitute another fundamental characteristic of life (Glass,
2001). Their interplay represents an inherent property of both, liv-
ing things and the activity of attending (Jones and Boltz, 1989).
As such, oscillatory mechanisms provide a realistic computational
basis to model the “adaptation to change by anticipation” (Fraisse,
1963, p. 18). DAT proposes that one or more attention oscillations
entrain to the rate and rhythm of external events (Large and Jones,
1999), i.e., adaptive oscillations lock into the temporal structure
of the stimulation, thereby establishing synchronized processing.
If confronted with a change in temporal structure, the oscillations
adjust their phase and period in order to maintain or to reestab-
lish synchronization. The result of this process is stimulus-driven
attending (Barnes and Jones, 2000). DAT provides a framework
capable of explaining how temporal structure guides attention on
a moment-to-moment basis and temporal dependencies within a
pattern, i.e. the possible influence of preceding temporal structure
on subsequent temporal processing, and the influence of global
temporal context (McAuley and Miller, 2007).
In the current study we used ERPs to investigate the impact of
regular and irregular temporal structure on the pre-attentive and
attentive processing of deviant events by means of auditory odd-
ball sequences. An oddball sequence consists of more (standard)
and less (deviant) frequent events, with the deviant event violating
some rule established by the standard. Pre-attentive and atten-
tive processing of this deviation is associated with distinct sets of
endogenousERPs.Withrespecttotheformerwefocusonmismatch
negativity (MMN), P3a, and reorienting negativity (RON), and with
respect to the latter on N2b and P3b.
In combination, MMN, P3a, and RON form the “distraction
potential” (Escera and Corral, 2007). The MMN has a fronto-central
scalp distribution and is elicited in response to a discriminable
change in auditory stimulation compared to a repetitive aspect
of preceding stimuli retained in short-term memory (Näätänen
et al., 1978, 2007; Garrido et al., 2009). Usually the MMN peaks
around 100–200ms after the presentation of the deviant event. It
reflects pre-attentive processing of sensory information as events
intime,includingauditorydurationdiscrimination(Näätänenetal.,
2004, 2007). The term MMN has largely replaced the classifica-
tion of this component as a subcomponent of the N2 under the
N2a label (Folstein and van Petten, 2008). The P3a is a fronto-
centrally distributed positive deflection evoked by task-irrelevant
salient events (Linden, 2005), whereas the later fronto-central RON
reflects restoration of the task-optimal selective attention set fol-
lowing distraction by task-irrelevant events (Schröger and Wolff,
1998).However,althoughthesecomponentsarerelatedtothepro-
cessing of deviant events in the environment they can be elicited
independent of each other (Horváth et al., 2008).
Withrespecttoattention-dependentprocessingweconcentrate
on another fronto-central N2 subcomponent, the N2b, associated
with the attentive detection of a deviant event, and the P3b, which
typically peaks around 300ms after the presentation of a deviant
event. Like the P3a, the more centro-parietal P3b is part of the P300
complex (Polich and Criado, 2006; Volpe et al., 2007). However,
each P3a is accompanied by a smaller P3b and vice versa (Linden,
2005). The P3b is commonly related to a task-relevant alteration
of a mental model of the environment, a stimulus-driven attention
mechanism, and memory processing (Linden, 2005; Polich, 2007).
The goal of the current study was to investigate how the con-
trast between regular, and therefore highly predictable temporal
structure, and irregular temporal structure would modulate the
aforementioned ERP components associated with various aspects
of the processing of deviance. In line with DAT, regular temporal
structure was expected to narrow the attentional focus and to pro-
mote synchronization, whereas irregular structure was expected
to widen the attentional focus and to promote reactive attending
(Jones et al., 2002). We consider the ERP modulation as an index for
thequalityofstimulus-drivensynchronization,thedynamicalloca-
tion of attention, and the quality of cognitive processes associated
with the processing of deviant events. Specifically, we hypothesize
that attention-dependent recognition of temporal regularity and
the subsequent use of this information to predict upcoming events
results in an enhanced amplitude of the N2b and P3b components
in response to deviants embedded in regular temporal structure
relative to those embedded in irregular temporal structure. This
enhancement should be similar for the pre-attentive processing
of deviance, and the distraction potential, i.e., MMN, P3a, and
RON, only if the underlying mechanism is also benefits from tem-
poral regularity. Alternatively, if attention-dependent temporal
processing is necessary to exploit regularity, pre-attentive tem-
poral processing should not benefit from temporal regularity. In
this case the distraction potential should be resistant against the
manipulation.
2. Materials and methods
2.1. Participants
Twenty-four right-handed volunteers (12 females) participated in the study.
Ages ranged from 19 to 30 years (mean: 24.4; SD: 2.8 years). All participants were
students at the University of Leipzig and were recruited via the database of the
Max-PlanckInstituteforHumanCognitiveandBrainSciencesinLeipzig.Noneofthe
participants reported any neurological dysfunction or a hearing deficit at the time
of testing. All participants gave their written informed consent and received a com-
pensatory fee. The study was approved by the Ethics Committee of the University
of Leipzig.
2.2. Stimulus presentation, EEG recording, and ERP analysis
The stimulus material consisted of two equidurational (300ms; 10ms rise and
fall) sinusoidal tones. The tones were used to generate a temporally regular, i.e.
isochronous, and a temporally irregular, i.e. random, auditory oddball sequence
(Fig.1).Thelatterwascreatedbyvaryingthedurationoftheinter-stimulus-interval
(ISI) between individual tones. Whereas the ISI was 600ms in the isochronous
sequence, it was randomly assigned from a range between 200 and 1000ms (nor-
mallydistributedaroundanaverage600ms)intherandomsequence.Thesespecific
parameters were chosen in order to take into consideration the privileged status
of simple integer ratios and intervals lasting about 600ms (Fraisse, 1982; Essens,
1986; Martin et al., 2007). An average SOA of 900ms is still within the range of
optimal tempo sensitivity (Drake and Botte, 1993), as well as the synchronization
range (Fraisse, 1982). The boundary between short-range and attention-dependent
longer-range temporal processing mechanisms is commonly associated with val-
ues close to 1000ms (Buhusi and Meck, 2005; Lewis and Miall, 2006). However, the
mechanism underlying attention-dependent temporal processing is probably sen-
sitive to intervals ranging from hundreds of milliseconds to seconds (Meck et al.,
2008).
The two tones differed in frequency (600Hz for standards and 660Hz for
deviants). Each oddball sequence comprised 512 standard and 128 deviant tones,
corresponding to a total of 640 tones and a standard-to-deviant ratio of 4:1.
Presentation 12.0 (Neurobehavioral Systems) running on a Windows PC was
used to create the pseudorandomized oddball sequences and to present the stimuli
viatwoloudspeakers.Pseudorandomizationensuredthatnomorethantwodeviant
events could appear in a row. The 600ms ISI in the isochronous sequence resulted
in a 1:2 ratio for the duration of the filled stimulus intervals and the empty ISI
intervals.Theorderofthesesequenceswaspseudo-randomizedacrossparticipants.
After the presentation of the first sequence, participants were given a 5min break.
Theexperimentwassplitintotwosessionsontwoconsecutivedays.Allparticipants
started with the pre-attentive session followed by the attentive session to preclude
familiarity effects.

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Fig.1. Stimulussequences.Exemplarysectionsofisochronousandrandomstimulus
sequencesconsistingofstandard(S)anddeviant(D)sinusoidaltones.SOA=stimulus
onset asynchrony. The figure in parentheses indicates the global average across the
random sequence.
TheEEGprocedurewasidenticalinbothsessions.DuringtheEEGrecordingpar-
ticipants sat in a sound-attenuated booth in front of a monitor. Ag/AgCl electrodes
mounted in an elastic cap according to the 10–20 International system were used to
record the EEG from 59 scalp sites with a sampling rate of 500Hz. An anti-aliasing
filter of 135Hz was applied. Online reference was placed on the left mastoid and the
sternum served as ground. Besides the EEG, horizontal and vertical electrooculogra-
phywererecorded.Electrodeimpedancewaskeptbelow5k?.EEP3.2(Max-Planck
Institute for Human Cognitive and Brain Sciences, Leipzig, Germany) was used to
process the data. All data were re-referenced offline to averaged mastoids. Prior to
subsequent analyses, EEG epochs lasting from 100ms pre-stimulus onset to 450ms
post-stimulus onset were scanned by an automatic algorithm to reject eye move-
ments, blinks, muscle artifacts, and electrode drifting. Trials exceeding 30?V (eye
channels) or 40?V (CZ) were rejected. An additional manual rejection of trials con-
taining artifacts or electrode drifting was performed after visual inspection. All
epochs of events corresponding to the presentation of a standard after a deviant
as well as a deviant following another deviant were generally rejected. Remaining
epochs were averaged for each participant and for the whole group.
Statistical analyses were performed using SAS 8.20.20 (SAS Institute Inc., Cary,
USA) for subsets of electrodes in six regions of interest. These regions included left-
anterior(AF7,AF3,F9,F7,F5,F3),left-central(T7,C5,C3,TP7,CP5,CP3),left-posterior
(P7, P5, P3, PO7, PO3, O1), right-anterior (AF8, AF4, F10, F8, F6, F4), right-central (T8,
C6, C4, TP8, CP6, CP4), and right-posterior (P8, P6, P4, PO8, PO4, O2) electrode sites.
Based on visual inspection and preparatory timeline analyses on mean amplitudes
for consecutive windows of 25ms from stimulus onset up to 450ms post-stimulus
onset, 100–200ms MMN, 225–325ms P3a, and 325–450ms RON windows were
selected for the subsequent statistical main analyses for the pre-attentive session,
while 125–225ms N2b and 250–450ms P3b windows were selected for the atten-
tive session. Timeline analyses consisted of separate 2×2×2×3 ANOVAs with
factors type (isochronous vs. random), condition (standard vs. deviant), hemisphere
(left vs. right) and region (anterior vs. central vs. parietal) for each 25ms window.
2.3. Tasks
In the pre-attentive session, participants were asked to watch a silent video clip
(Deep Blue, 2003) and to fill out a short questionnaire about the video after the
session. Prior to testing, participants were told that they should concentrate on the
video and to ignore any auditory input. In contrast, participants were asked to con-
centrateonthetonalsequencesandtosilentlycountthedeviantsembeddedineach
sequence while fixating an asterisk displayed on the monitor during the attentive
session.Participantsreportedtheresultofcountingaftereachsequence.Thus,while
thesequencesthemselveswereattendedto,explicitattentiontotemporalstructure
was not task-relevant. Rather, temporal structure served as an implicit attractor for
attention-dependent temporal processing. An additional sequence of eight tones,
including five deviants, was appended to each random sequence in order to avoid
identical numbers of deviants in each sequence. These additional tone sequences
were excluded from all ERP analyses.
3. Results
3.1. Pre-attentive session
The percentage of correct answers given in the questionnaire
after the pre-attentive session was 84.38 (SD 16.17), indicating
that participants did indeed pay attention to the content of the
videoclip.Bothisochronousandrandomoddballsequencesevoked
reliable MMN, P3a, and RON ERPs (Fig. 2A and B).
To ensure that each sequence elicited the desired compo-
nents, all ERPs of interest were analyzed in separate 2×2×3
ANOVAs with the factors condition (standard vs. deviant), hemi-
sphere (left vs. right), and region (anterior vs. central vs. posterior).
Where required, Greenhouse–Geisser correction was applied
to the results reported in the following. In the isochronous
sequences, there was a main effect of condition in the MMN
(F(1,23)=53.51, p<.01), the P3a (F(1,23)=10.20, p<.01), and the
RON (F(1,23)=6.12, p<.03) time-window. In the MMN time-
windowweobservedasignificanttwo-wayinteractionofcondition
and region (F(2,46)=14.22, p<.01), indicating that the condition
effect was strongest at anterior sites (F(1,23)=60.76, p<.01). In
the random sequences we observed a similar pattern for condi-
tion in the MMN (F(1,23)=55.52, p<.01), the P3a (F(1,23)=6.34,
p<.02), and the RON (F(1,23)=13.19, p<.01) time-window. Again,
there was a significant interaction in the MMN window of condi-
tion and region (F(2,46)=14.22, p<.01), revealing that the effect
was strongest at anterior sites (F(1,23)=49.40, p<.01).
For the direct comparison of the effects obtained with
isochronous and random temporal structure, we calculated differ-
encewavesbysubtractingstandardfromdeviantERPresponses.All
subsequent analyses were performed on these difference waves.
In contrast to random temporal structure, visual inspection sug-
gested slightly more negative and positive effects as a function
of isochronous temporal structure for the MMN and the P3a,
respectively (Fig. 2C). However, contrasting the effects by means
of 2×2×2 ANOVAs with factors type (isochronous vs. random),
hemisphere(leftvs.right),andregion(anteriorvs.centralvs.poste-
rior)onlyconformedaneffectofregion(F(2,46)=15.23,p<.01),but
not of type (F(1,23)=.31, p=.58) and no significant interaction. To
further validate this finding, we narrowed the critical time window
down to 50ms and centered it in the optimal range (125–175ms).
However, this procedure did not change the initial result, type
(F(1,23)=1.37, p=.25). The same type of ANOVA was conducted
for the P3a and the RON time-window, none of which yielded
significant results. Narrowing the critical range for the P3a time-
window to 250–300ms did not change this outcome. Thus, we did
not observe a significant influence of temporal regularity on the
cognitive mechanisms underlying the pre-attentive processing of
the deviant events.
3.2. Attentive session
One-sample t-tests yielded no significant differences between
the individual values reported by the participants in the count-
ing task and the actual number of deviants embedded in the
isochronous (actual number: 128; mean result: 128.21, SD: 4.35;
t(1,23)=.23, p=.81) and in the random (actual number: 133;
mean result: 133.25, SD: 4.48; t(1,23)=.27, p=.79) sequence. These
results confirmed that participants indeed paid attention to the
tonal sequences. The same type of 2×2×3 ANOVA as for the pre-
attentivesessionwasconductedtotestforthepresenceoftheERPs
of interest in the attentive session (Fig. 3A and B).
Both the isochronous and the random oddball sequence elicited
significant N2b and P3b components. In the N2b time-window
we obtained significant effects of condition in the isochronous
(F(1,23)=4.29, p<.05) and in the random (F(1,23)=6.32, p<.02)
sequence. In both sequence types interactions of condition and
region (F(2,46)=14.90, p<.01; F(2,46)=13.14, p<.01) indicated
that the effect was present at anterior (F(1,23)=7.17, p<.02;
F(1,23)=8.75, p<.01) and at central sites (F(1,23)=8.80, p<.01;
F(1,23)=12.26, p<.01). The effect of condition emerged also in the
P3b window in isochronous (F(1,23)=58.14, p<.01) and random
sequences (F(1,23)=42.77, p<.01). An interaction of the factors
condition and region in both sequences (F(2,46)=79.10, p<.01;
F(2,46)=63.48, p<.01) indicated that the effect of condition was
present at central sites (F(1,23)=78.77, p<.01; F(1,23)=48.35,
p<.01), but that it was stronger at posterior sites for isochronous
(F(1,23)=98.07, p<.01) and random sequences (F(1,23)=67.17,
p<.01).

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Fig. 2. Pre-attentive session. Averaged EEG responses for standards (blue) and deviants (red) at two fronto-central electrodes in the pre-attentive session complemented
by MMN, P3a, and RON scalp distributions for isochronous (A) and random (B) temporal structure. Differences waves and difference distributions contrast ERP effects for
isochronous (blue) and random (red) temporal structure (C).
Again, difference waves were calculated for the subsequent
comparison of the isochronous and the random sequence. In the
N2b time-window, direct comparison of the ERP effects obtained
with isochronous and random stimulation (Fig. 3C) yielded neither
a significant effect of type (F(1,23)=.38, p=.55) nor a significant
interaction involving this factor. Narrowing the critical window
to 175–225ms did not change this result, type (F(1,23)=.08,
p=.78.
WhilethemaineffectoftypewasnotsignificantintheP3btime-
window (F(1,23)=1.92, p=.18), there was a significant interaction
of type and region (F(2,46)=7.94, p<.01). Type approached signifi-
cance at central sites (F(1,23)=3.99, p=.058), but was significant at
Fig. 3. Attentive session. Averaged EEG responses for standards (blue) and deviants (red) at two centro-parietal electrodes in the attentive session complemented by N2b
and P3b scalp distributions for isochronous (A) and random (B) temporal structure. Differences waves and difference distributions contrast ERP effects for isochronous (blue)
and random (red) temporal structure (C).

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M. Schwartze et al. / Biological Psychology 87 (2011) 146–151
posterior sites (F(1,23)=4.76, p<04) confirming a larger P3b effect
in isochronous than in random sequences.
4. Discussion
In the current study we investigated the impact of tempo-
ral regularity on ERPs associated with pre-attentive and attentive
processing of auditory deviant events. The applied experimen-
tal paradigms reliably elicited MMN, P3a, RON, N2b, and P3b
components. Regular temporal structure resulted in a larger
attention-dependentP3beffectrelativetoirregulartemporalstruc-
ture. The results support the dissociation of pre-attentive and
attention-dependent temporal processing mechanisms. Further-
more, they confirm concepts of a dynamic allocation of attention
put forward in DAT (Large and Jones, 1999).
In the pre-attentive session, we did not observe a substantial
impact of temporal regularity on three ERP components reflect-
ing different aspects of deviant event processing. Unlike previous
studies which used a limited number of SOAs (two or three) and
report an effect of temporal regularity on MMN amplitude (Imada
et al., 1993; Takegata and Morotomi, 1999; Moberget et al., 2008),
the current study used online randomization, i.e. no predefined
set of SOAs, to generate irregular temporal structure. Takegata and
Morotomi (1999) conclude that increasing the number of SOAs in
a sequence, not irregular timing, is the reason for the observed
influence, as different SOAs may strengthen different memory
traces. This hints at a qualitative difference between previous stud-
ies and the current study. Whereas continuous presentation of
many stimulus repetitions with a limited number of predefined
and well distinguishable SOAs may evoke different, albeit weaker,
memory traces, online randomization in the current study was
only limited by temporal range, which in turn may prove tem-
poral structure unreliable and dispensable. Crucially, in this latter
case successive stimuli may still strengthen the same memory
trace. However, even the random sequence conveys some regu-
larity, as the sequential presentation of similar events in a specific
time-window constitutes a form of regularity in itself. Thus, the
question arises, how repetitive presentation of predefined tempo-
ral structure (“the SOA is either short or long”) compares to relative
temporal structure (“the SOA is 900ms on average”) in generating
a random sequence, and how this difference affects deviance pro-
cessing. With independently varied ISIs and SOAs, Takegata et al.
(2001) found a larger MMN for constant temporal structure in
comparison to either constant ISI, constant SOA, or neither con-
stant conditions, but no difference between the latter. However,
devianteventsinthisstudyweretonesbeingpresented“tooearly”,
thereby merging temporal structure and deviance levels. By using
frequency deviants we separated deviance from temporal struc-
ture. Nevertheless, for the MMN and the P3a, but not the RON,
visual inspection suggested slightly more pronounced effects for
deviantsembeddedintheisochronoussequence.However,thisdif-
ference was not statistically significant. Morphological differences
and the presence of a significant RON for regular and irregular con-
textsmayindicateshortepisodesofattention-dependenttemporal
processing in the pre-attentive session following distraction by a
task-irrelevant deviant event. Correspondingly, one cannot com-
pletely rule out episodes of divided attention between the tonal
stimuli and the silent video clip. Yet, processing of the deviant
events in the pre-attentive session was neither significantly facili-
tated nor hindered by the temporal manipulation employed in this
study.Whencontrastedwiththeresultsfromtheattentivesession,
thisindifferencebearsimplicationsfortemporalprocessingandthe
allocationofattentionalresources.Whentaskinstructionsrequired
to not attend to the auditory stimuli, an internal representation
of temporal structure may still be encoded via pre-attentive tem-
poral processing. Correspondingly, we did not find an indication
of stimulus-driven synchronization in the pre-attentive session.
Decoding of such internal representation of temporal structure
and the recognition of temporal regularity likely require addi-
tional attention-dependent temporal processing routines such as
duration discrimination of successive intervals (Meck et al., 2008).
Once a pattern has been recognized, subsequent processing should
be facilitated as it allows predicting the temporal locus of future
events, to focus attention on specific information, and to initiate
behavior anticipatorily.
During the early stages of auditory processing it is probably
more relevant to rapidly detect events and to generate precise
internal representations of temporal structure. This may be nec-
essary to encode temporal detail before this information becomes
erratic due to long neural transmission lines and numerous
synapses (Adams, 2006). This function may involve the cerebel-
lar temporal processing system and its connections to the earliest
stages of auditory processing (Petacchi et al., 2005). The audi-
tory cortex may keep reference to the immediate auditory past
and future (Näätänen et al., 2001), probably processing temporal
regularity without depending on it. This would explain the robust-
ness of the pre-attentive ERPs against the temporal manipulation.
Furthermore, given that temporal irregularity or deviation from a
temporalpatternmayrepresentimportantinformationinitself,the
initial processing should be comparable, independent of whether
the input indeed conveys regularity or whether it is irregular.
In contrast, we observed an influence of temporal regularity
in the attentive session. Whereas the earlier N2b effect remained
unaffected, the later P3b effect was significantly larger for deviant
events embedded in isochronous context. In line with DAT, this
mayreflectstimulus-drivensynchronizationofattentionthatleads
to facilitation in cognitive processing. Furthermore, this dissoci-
ation hints at a difference in the time-course of the underlying
processes. With respect to the moment at which attention affects
temporal processing, these results speak for an impact of atten-
tion on later mechanisms relative to those represented in the
earlier N2b. The influence of attention-dependent temporal pro-
cessing was not reflected in the detection of deviant events. It
became apparent in subsequent memory processing and model
updating, possibly referring to successful memory storage in order
to facilitate retrieval and recognition (Polich, 2007). These pro-
cesses may involve the ongoing evaluation of an interval-based
representation of temporal inter-event relations in order to track
regularity. Interestingly, the cortical generators of the P3b include
thetemporo-parietaljunctionandtheinferiorparietallobe(Linden,
2005), an area that is also associated with implicit temporal pro-
cessing (Coull and Nobre, 2008; Wiener et al., 2010). Furthermore,
at this stage, temporal and memory processing may draw upon
the same prefrontal capacities (Lustig et al., 2005; Lewis and Miall,
2006).
The observed influence of temporal regularity in the atten-
tive session was independent of explicit attention to time or an
explicit estimation of time. As long as attention was directed
towards the auditory stimuli, temporal structure was processed
and exploited without estimating time. The current results thereby
offer an example for the interplay of top-down, task-specific atten-
tion and stimulus-driven attending in order to guide attention
along a sequential stimulation. In line with previous findings
(Schmidt-Kassow et al., 2009) the P3b should hence be consid-
eredasanindexforthequalityofstimulus-drivensynchronization.
The specific pattern of results suggests that the attentive detection
of a deviant event functions independent of temporal regularity,
whereas subsequent processes benefit from temporal predictabil-
ityofthestimulussequence.Wewereabletoshowthattemporally
regular stimulus presentation (the “when” aspect of sensory input)
supportstheattentiveprocessingofformalstimuluscharacteristics

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M. Schwartze et al. / Biological Psychology 87 (2011) 146–151
151
(the “what” aspect of sensory input). Although the current exper-
iment restricted the formal aspect to a single difference in pitch,
we expect this principle to be effective in other modalities and in
complex settings such as music and speech processing (Kotz and
Schwartze, 2010). This in turn may hint at a predisposition for con-
stant attempts to synchronize cognition and action to perceived
regularity in the succession of changes in the environment.
Acknowledgements
The third author was supported by a grant from the German
Research Foundation (DFG SCHM 2693/1-1).
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