despite the presence of constantly changing sensory input , we perceive a continuous and unitary interpretation of the current state of the environment at all times .
sensitivity to change necessitates high temporal resolution for stimulus segregation , while stability of perceptual representations requires integration of signals over time .
temporal segregation can occur with millisecond resolution . in humans , flicker - fusion thresholds  the frequency at which intermittent light stimulation appears continuous  range typically between 40 and 60  hz .
temporal offsets as brief as 520  ms can be detected between two sequential stimuli [ 2 , 3 ] , and first - order motion detection can exceed 30  hz .
neural responses in retinal ganglion cells , the lateral geniculate nucleus ( lgn ) , and even in primary visual cortex   can track temporal properties driven by fast external stimulation .
this high temporal resolution of visual signals supports sensitivity to change and may reduce motion blur ( [ 8 , 9 ] ; for a review , see .
temporal segregation sharply contrasts with the need to integrate information over extended intervals of time to perceive the  stability of object identity and location [ 11 , 12 ] , to accumulate information to reach reliable perceptual decisions , and to understand sensory signals related to self and object motion .
temporal integration is supported by the brain s capacity for self - organized information retention and is based on persisting neural activity after the input has already vanished [ 14 , 15 ] .
an example of temporal integration is the finding that two flashes separated by a brief delay may be perceived as a single item when the inter - stimulus blank period is less than 50  ms .
similarly , in forward- and backward - masking paradigms , integration of target and mask is reported for delays of 80 to 120  ms .
another example of integration is the perception of apparent motion between two briefly flashed stimuli , which can occur across a temporal gap of hundreds of milliseconds [ e.g. , 18 ] . here
, we aim to characterize the neural mechanisms that determine whether two stimuli are temporally integrated into a single event or , instead , perceived as separate entities . to this end
, we directly contrast the time course of stimulus segregation and integration with a variant of the missing - element task [ 19 , 20 ] . human observers viewed the same sequence of two patterns separated by a brief inter - stimulus interval ( isi ) but were instructed to either segregate or integrate stimuli over time ( figure  1a ) . on integration trials ,
participants were instructed to report the location of the missing element , which was the single cell in a virtual grid where no item was presented in either the first or the second display .
this task was only possible when the two displays were combined over time [ 19 , 20 ] . on segregation trials , in contrast , the task was to report the location in which an odd element ( half annulus ) was shown in both displays .
performance in the latter task required the two displays to be segregated in time , since integration of the two half annuli rendered them indistinguishable from a full annulus . as expected , performance was near perfect for the integration task with a brief isi and worsened with longer delays [ 19 , 20 ] , while segregation showed the opposite pattern ( figure  1b ) .
for each subject , we determined the isi at which performance on the two tasks was matched ; yielding equal proportions between correct / incorrect trials for both segregation and integration tasks ( figure  1c ) .
thus , this stimulus display allowed us to match task difficulty and to use the identical physical stimulus while measuring the brain mechanisms underlying temporally separate or combined visual percepts .
we tested the hypothesis that the visual system coordinates stimulus segregation and integration over time by aligning the phase of slow - frequency brain oscillations to the onset of newly arriving sensory samples .
first , we used magneto - encephalography ( meg ) to compare the converging measures of stimulus - evoked fields , frequency - specific phase coherence , and multivariate pattern analysis ( mvpa ) decoding between segregation and integration trials . across all three meg measures , we found a task - specific pattern of brain states for either segregation or integration in alternation at 3  hz after stimulus onset , possibly due to a phase shift in ongoing brain oscillations .
consistent with our hypothesis , oscillatory activity in the pre - stimulus time interval was already informative about both task processing and behavioral outcome , with opposite phases in the theta frequency band for segregation / integration , as well as distinguishing correct / incorrect trials for each task separately . in a second study , we investigated the role of saccadic eye movements in shifting slow - frequency alternations between task states .
like stimulus onset , each saccade confronts the visual system with a transient change in sensory input , creating a conflict between stimulus segregation and integration .
analogous to the temporal patterns decoded from the meg data when aligned to stimulus onset , the densely sampled time courses of task performance alternated at a rate of 35  hz when aligned to the onset of each new eye fixation .
together , these findings uncovered a counter - phase alternation between pattern segregation and integration in visual processing that determined perceptual experience .
the isi that yielded equal proportions of correct trials for both tasks was determined individually for each subject prior to running the meg experiment ( figure  1b ; see supplemental information ) .
integration performance decreased , and segregation increased with longer isi , with isi explaining more than 90% of the variance ( figure  1b ) .
for both experiments , performance did not differ significantly between tasks : meg experiment , t(18 )  = 0.4 , n.s .
( not significant ) ; eye movement experiment , t(27 )  = 1.8 , n.s . )
( figure  1c ) . the analysis of meg data focused on differences in neural activity , for an identical stimulus and with matched task difficulty , as a function of task ( integration / segregation ) and performance ( correct / incorrect ) .
this involved the analysis of event - related fields ( erfs ) , inter - trial phase coherence ( itc ) , and mvpa decoding in the post - stimulus time period , plus theta frequency band phase bifurcation in the pre - stimulus period .
first , we investigated stimulus - evoked activity in the time interval ranging from the second stimulus display onset to  + 500  ms afterward , as measured by the erf and itc ( see supplemental information ) .
statistical significance between conditions was assessed by means of nonparametric cluster - based permutation t  statistics , effectively controlling for multiple statistical comparisons at multiple time , frequency , and sensor samples ( see supplemental information ) . both measures ( erf and itc averaged over frequencies between 5 and 25  hz ) resulted in strong response peaks relative to pre - stimulus baseline periods : z(erf )  = 2.5 , and z(itc ) 
= 2.3 . as shown in figure  2 , the relative strength of the evoked activity alternated between tasks , time locked to stimulus onset . for the erf
, segregation trials evoked a stronger response from 160 to 290  ms after display 2 onset ( cluster - corrected p  < 0.004 ) .
then , the pattern reversed so that the same sensor locations displayed stronger evoked amplitude in integration trials from 300 to 450  ms ( cluster - corrected p  <  0.007 ; figure  2a ) . averaged over this significant cluster of sensors ( highlighted with white dots in figure  2c ) , evoked activity alternated four times between segregation and integration trials in time windows of approximately 150  ms in duration , starting from the onset of the stimulus sequence until  + 600  ms ( figure  2c ) : 250 to 100  ms , t(18 )  = 1.9 , n.s . ; 50 to  + 100  ms , t(18 )  = 3.7 , p  < 0.002 ;  + 150 to 300 , t(18 )  = 5.3 , p  < 0.001 ;  + 300 to  + 450 , t(18 )  = 6.2 , p  < 0.001 ;  + 450 to  + 600  ms , t(18 )  = 2.5 , p  < 0.024 ;  + 600 to  + 750  ms , t(18 )  = 0.5 , n.s . ) .
this erf effect could result either from differences in stimulus - evoked response amplitude or stimulus - reset phase coherence between conditions . in order to disentangle these possibilities , we estimated the amount of phase alignment to stimulus onset with itc .
both erf and itc activity peaked around 100  ms after  display 2 onset ( mean   sd : 120   56  ms for erf , and 98   31  ms for itc ; no latency difference , t(18 )  = 1.6 , n.s . ) , and the baseline - corrected effect sizes correlated moderately over subjects ( r  =  0.41 , p  < 0.085 ) . between tasks , we found a stronger itc  for segregation trials immediately after display 2 onset ( 0  to  + 150  ms ) at 67  hz within a central gradiometer sensor cluster ( figure  2b ; cluster - corrected p  < 0.001 for the time interval from 200 to  + 500  ms and the frequency range between 5 and 25  hz ) . confirming previous results using integration masking
, these findings suggest that the initial stronger response for segregation trials , evident in the erf , was , at least in part , due to stronger phase coherence of slow - frequency oscillations .
we used mvpa classification to further investigate the differences in the post - stimulus time period as a function of task ( integration / segregation ) and behavioral outcome ( correct / incorrect ; supplemental information ) .
task was decodable as early as 100  ms after the second stimulus display onset ( cluster - corrected zcor  = 3.1 , p  < 0.002 ) , peaked at 260  ms ( zcor  = 3.7 , p  < 0.001 ) , and persisted for almost an entire second ( zcor  = 3.2 , p  < 0.002 at 950  ms ; figures 3a and 3b ) . across subjects , the highest decoding accuracy ( z(task decoding )  = 2.3 ; measure and baseline intervals identical to those mentioned earlier ) correlated significantly with erf ( r  = 0.55 , p  < 0.015 ) and itc effect sizes ( r  = 0.59 , p  < 0.008 ) but peaked in a significantly later time interval ( mean   sd : 353   96  ms ; decoding versus erf peak latency , t(18 )  = 9 , p  < 0.001 ; versus itc ,
topographical maps and source projections ( see supplemental information ) revealed two temporally distinct time windows ( 150450  ms and 600900  ms ) , with maximal decoding accuracy at occipital - parietal sensor locations and occipital - parietal sources ( figure  3c ; table s1 ) .
the meg signal also contained information about task outcome in terms of correct or incorrect trials , separately for integration or segregation blocks . for segregation
, we found significant above - chance decoding of outcome by 140  ms after display 2 onset ( zcor  = 2.1 , p  < 0.037 ) .
however , outcome decoding was most accurate and reliable in the time window from around  + 500 to  + 900  ms , when the participants response was probed ( figures 3a and 3b ; see also figure  2a ) ( for segregation : peak sample at 570  ms , zcor  = 3.7 , p  <
0.001 ; for integration : peak sample at 620  ms , zcor  = 2.3 , p  < 0.022 ) . for both integration and segregation blocks , the lcmv beamformer algorithm ( see supplemental information ) suggested neural generators in occipital areas as source solutions for outcome decoding , indicating that the mvpa signal reflected perceptual rather than purely decisional or motor processes ( figures 3d and 3e ; table s1 ) .
statistical significance was assessed by means of cluster - corrected z statistics of decoding accuracy against chance level , using a threshold - free method for clustering and a monte carlo permutation approach for multiple comparison correction ( see supplemental information ) .
meg - mvpa decoding was equally robust when the sensor topographies were normalized for overall response amplitude ( figure  s1 ) and/or when chance level was estimated based on random permutations of the data partitions ( in contrast to assuming chance level as 50% a priori ; figure  s2 ) .
the temporal generalization method ( see supplemental information ) was used to characterize the temporal pattern of task decoding and its interaction with task outcome ( correct versus incorrect ) .
as shown in figure  4a , we generated matrices mapping each classifier s task - decoding accuracy in the training  set against the entire testing time interval from 500 to  + 1,500  ms , relative to display 2 onset ( in steps of 10  ms ) .
the strong above - chance decoding accuracy along the main diagonal suggests a series of distinct patterns of brain activity for integration versus segregation trials ( zcor  = 3.3 , p  < 0.001 ; training / testing time ,  + 280/270  ms ) . on - diagonal , above - chance decoding was accompanied by off - diagonal , below - chance accuracy , with consistent and highly significant misclassification of integration and segregation trials during the earlier and later intervals ( around 150300  ms before and after ) on the basis of the trained pattern at a given time point ( zcor  = 3.3 , p  < 0.001 ; training / testing time ,  + 780/500  ms ; figure  4a ) .
this pattern suggests that the signal dissociating task processing reoccurred at a  later time point , but with reversed polarity .
the pattern of reversed decoding persisted for almost an entire second after stimulus onset ( figures 4a and s3 ; table s2 ) , originated in occipital brain regions for both the on- and the off - diagonal signals ( figure  4b ; table s1 ) , and alternated at a rate of approximately 3  hz ( figures 4c and 4d ) . the strength of task decoding ( segregation versus integration trials ) interacted with task outcome .
decoding was significantly better in correct trials ( used in both training and testing sets ) , with more accurate classification for the on - diagonal signal and stronger misclassification for the off - diagonal signal ( figures 4c and s4 ; tables s3 and s4 ) .
in other words , incorrect segregation / integration trials were more likely to be classified as belonging to the other task , respectively .
this resulted in significantly stronger 3-hz amplitude in decoding accuracy for correct trials ( 3.3-hz amplitude peak , correct versus incorrect , t(18 )  = 3.2 , p  < 0.006 ; figure  4d ) .
consistent with univariate analysis , mvpa temporal generalization confirmed that task processing alternated at a rate of approximately 3  hz . however , the most prominent pattern between segregation and integration signals was the robust phase opposition in the first two 150-ms time windows after the stimulus - evoked response . additionally , we found indications for further alternations but with decaying signal amplitude from the time - locking event ( figures 2a , 2c , 4c , and 4d ) . in order to estimate the longevity of the task - dissociating pattern and
how often the signal alternated between segregation and integration states , we compared the explained variance ( least - square ) in the task - decoding signal between the best - fitting models from three different model classes : oscillatory ( sinusoid function , or s ) , decaying ( gabor function , or d ) or dampened oscillatory ( sinusoid function  decay function , or ds ; see supplemental information ) .
the best - fitting dampened sinusoid function provided a strong explanation for the observed mean decoding signal ( r  = 0.89 ; figure  s5 ) , accounting for significantly more variance compared to the optimal sinusoid function ( r  = 0.31 ) or monotonic response decay function ( r  = 0.61 ; change in r 
  f test : ds versus s , f(1 , 147 )  = 781.7 , p  < 0.001 ; ds versus d , f(2 , 147 )  = 185.9 ,
p  < 0.001 ) . averaged across the single - subject parameter estimates , both steady and dampened sinusoid functions were best fit with a signal alternation rate around 3  hz ( mean frequency   sd [ f ] : for s , f  = 2.9   0.5  hz ; and for ds , f  = 3.4   0.4  hz ) .
in contrast to a longer - lasting ongoing alternation between tasks , however , the dampened oscillation model accounted for the signal variance foremost in a limited time window of one or two cycles from stimulus onset ( mean   sd for full - duration half maximum [ fdhm ]  = 395   224  ms , 1.3   0.5 cycles ) .
the dampened oscillatory pattern might be evident of a phase reset in ongoing brain oscillations [ 23 , 24 ] , aligning the optimal phases for segregation and integration to the onset of the stimulus display . in order to directly test whether a shift in oscillatory phase accounted for the alternations between task signals observed here , we analyzed the oscillatory activity in the pre - stimulus period . if the observed , stimulus - evoked alternations were due to a phase shift in ongoing oscillations , the phase information of slow - frequency oscillations before stimulus onset should be informative about task processing and/or behavioral outcome .
to this end , we first extracted the instantaneous phase in the theta frequency band ( 3- to7-hz band - pass - filtered time courses ; figure  5a ) for the 1-s time period preceding the onset of stimulus display 1 with a hilbert transform . then , we calculated the phase bifurcation index ( pbi )   between segregation and integration trials , as well as between correct and incorrect trials for each task separately .
statistical significance was assessed with a permutation approach based on 10,000 surrogate datasets with shuffled condition labels and corrected for multiple comparisons with the false discovery rate procedure ( see supplemental information ) .
a positive pbi indicates that two conditions exhibit strong phase coherence ( as measured with  itc ) but at polar - opposite phase angles : pbi  = ( itccond1  itcall trials )  ( itccond2  itcall trials ; see supplemental information ) .
consistent with our hypothesis , we found significant phase bifurcation in the pre - stimulus interval between segregation and integration trials ( smallest p  < 0.01 ) , mainly over occipital sensor locations ( 19/102 significant magnetometer sensors , p  < 0.05 ; figure  5b ) .
in addition , for each task separately , we observed significantly stronger phase opposition than expected by chance between correct and incorrect trials over temporal sensor locations ( for integration : smallest p  < 0.023 , ten significant sensors ; for segregation : smallest p  < 0.021 , six significant sensors ; figures 5c and 5d ) .
we found positive phase bifurcation indicative of phase opposition between tasks , mainly in the pre - stimulus time window .
after stimulus onset , phase coherence ( itc ) was stronger in segregation trials ( as also shown in the stronger itc effect reported earlier ) , which resulted in a negative pbi for task processing due to stronger phase locking to stimulus onset in one condition ( figure  s6 ) .
next , we tested whether this pattern of alternations between temporal integration and segregation in the theta frequency band has perceptual consequences . in the meg study , we predicted that stimulus onset would lead to a phase reset of ongoing slow - frequency oscillations , and we were able to trace the effects of the onset on neural signals at subsequent points in time . for behavioral oscillations , however , it is necessary to define a reset point prior to the stimulus / probe in order to trace the time course of performance aligned to that event [ 26 , 27 , 28 , 29 ] .
we hypothesized , based on both theoretical reasons [ 30 , 31 ] and neurophysiological evidence for theta - band phase resets after saccades [ 32 , 33 , 34 , 35 , 36 ] , that fluctuations would be aligned to new fixations .
moreover , it has been shown that phase alignment influences the temporal precision of neural coding [ 32 , 37 ] , leading to the hypothesis that segregation performance , which relies on high temporal precision , might be best after a saccade - induced reset .
on each trial , we measured the onset of an 8 saccadic eye movement and then timed stimulus presentation relative to eye fixation onset .
stimuli were presented over the first 500  ms ( 20-ms time bins , 50-hz sampling ) in experiment 2a ( expt 2a ) or the entire first second after eye - fixation onset in experiment 2b ( expt 2b ) ( 40-ms bins , 25  hz ; figure  6a ) .
subsequently , we calculated the proportion of correct responses at each time point  ( dense sampling ; see supplemental information ) .
we hypothesized that the saccade , like the stimulus onset in the meg study , would create a phase reset and lead to alternations in performance , with an initial benefit for segregation trials .
consistent with this hypothesis , the temporal dynamics for segregation and integration differed significantly with alternations between the two tasks in terms of accuracy occurring in 150-ms time windows for both expts 2a and 2b ( figure  6b ; tables s5 and s6 ) . following the logic used in previous studies measuring behavioral oscillations [ 26 , 27 , 28 , 29 ] , we fourier - transformed the accuracy time courses for each task and the difference time course between tasks ( segregation - integration ) in order to reveal temporal structure in data .
statistical reliability of the peaks in the fourier spectra was assessed with a nonparametric permutation approach based on shuffled surrogate data .
the spectral amplitude of the accuracy - difference time course between tasks revealed a significant peak at 5.2  hz ( expt 2b : permutation test , p  < 0.009 ; figure  6c ) .
likewise , the phase of the complex fourier vectors across observers at 3  hz deviated significantly from a uniform distribution ( rayleigh test : expt 2a , 3.75  hz , z  = 4.2 , p  < 0.0125 ; expt 2b , 3.1  hz , z  = 5 , p  < 0.005 ) and was significantly more concentrated ( inter - observer coherence [ ioc ] ; see supplemental information ) compared to random time series ( permutation test : expt 2a , p  < 0.015 ; expt 2b , p  < 0.004 ; figure  6d ) . to confirm the phase opposition between the two tasks , we assessed the average angular phase relation across observers between integration and segregation with the pbi that is sensitive to strong phase locking across observers ( ioc ) at polar - opposite angles (; see supplemental information ) . a counter - phase relationship indicative of a phase shift between integration and segregation time series
was found at 3  hz in both experiments ( permutation test : expt 2a , 3.3  hz , p  < 0.004 ; expt 2b , 3  hz , p  < 0.009 ; figure  6e ) .
taken together , the time course , spectral amplitude , and spectral phase analyses indicate that integration and segregation performance alternated in the theta range ( 35  hz ) and in counter - phase locked to the new eye - fixation onset .
similar to the modeling approach for the meg data , we estimated the longevity of these behavioral oscillations with least - square curve fitting of the accuracy - difference time course with a sinusoid function ( or s ) , a decaying function ( or d [ exponential ] ) or a combination of the two ( ds ) .
the average behavioral time course in expt 2a ( + 110 to  + 510  ms ) was equally well modeled by a sinusoid function ( f  = 3.6  hz , r  = 0.49 ) or dampened sinusoid function ( f  = 3.5  hz ; half - life [ t(1/2 ) ]  = 401  ms ( 1.4 cycles ) , r  = 0.47 ) , both explaining significantly more variance compared to a monotonic decay ( r  = 0.22 ; f test : s versus d , f(1 , 18 )  = 7.8 , p  < 0.012 ; ds versus d , f(2 , 18 )  = 4.2 ,
the behavioral time course ( + 160 to  + 1,000  ms ) was best fit with a dampened sinusoid function ( f  = 2.9  hz , t1/2  = 143  ms [ 0.4 cycles ] , r  = 0.57 ; figure  s5 ) , followed by a steady sinusoid function ( f  = 2.9  hz , r  = 0.33 ) , and then a decaying function ( r  = 0.22 ; f test : ds versus s , f(1 ,  19 )  = 9.3 , p  < 0.007 ; ds versus d , f(2 , 19 )  = 6.8 , p 
< 0.006 ; s versus d , f(1 , 19 )  = 4.3 , p  < 0.051 ) .
thus , in accordance with the meg results reported earlier in the text , the behavioral oscillations between integration and segregation decayed with increasing time from fixation onset , evident of short - lived phase synchronization triggered by the saccadic eye movement .
the findings reported here uncover the temporal coordination of opposing processing demands for segregation and integration . for meg , we found an alternating temporal pattern between segregation and integration in converging erf , itc , and mvpa measures , as well as pre - stimulus phase .
meg - mvpa task decoding correlated highly with classical measures of visual evoked activity ( erf , itc ) and spread over time in the caudal - to - rostral direction .
consistent with previous studies using electroencephalography , we found the strongest meg signatures of pattern integration / segregation in intervals after the first feed - forward sweep of visually evoked activity ( 150450  ms ) .
critically , neither peak intensity nor latency of any meg measures ( erf , itc , mvpa ) was correlated with the temporal offsets between the two stimulus frames for individual observers ( r  < 0.35 , all ps were n.s . ) .
hence , the latency in evoked activity between segregation and integration time courses does not simply reflect a short - lived effect of selecting different target displays , i.e. , selection of the first or second display for segregation or integration , respectively .
mvpa generalization showed that integration and segregation trials were predominantly decoded from the meg signal on the basis of a pattern that reverses polarity with a period of approximately 150  ms , consistent with a dampened 3-hz oscillation alternating for a limited time window of one or two cycles .
importantly , the mvpa decoding pattern between tasks ( segregation versus integration ) interacted with task outcome , consistent with its holding functional relevance for perception . to the best of our knowledge ,
this provides the first report of significant mvpa decoding of top - down signals ( i.e. , task instructions ) in visual cortex using meg , with decoding performance in line with recent reports decoding top - down factors using functional magnetic resonance imaging ( fmri ) . in the meg study , we measured alternations in segregation / integration time locked to stimulus onset .
time - frequency analysis of the pre - stimulus time period suggested that the post - stimulus neural signals were due to a phase shift in ongoing brain oscillations favoring either task in opposite phases in the theta frequency band . in natural viewing , however , it is more typically the case that the stimulus is continuously present but discretely sampled by saccadic eye movements at a rate of about 35  hz . in the second experiment , we show that the visual system aligns its susceptibility for segregation and integration to this overt sampling behavior .
when time locked to fixation onset , behavioral performance alternated in time in the theta frequency range , with a phase alignment similar to that of the stimulus - locked meg activity .
interestingly , performance , when time locked to either stimulus onset or fixation onset , was initially better for segregation .
one possible explanation is that performance in the segregation task relies on high temporal resolution . in terms of neural processing ,
high temporal resolution may reflect precision in spiking activity ; for a review , see .
such increases in spike rate precision have been linked to both ongoing and saccade - induced oscillations [ 32 , 37 ] . for perception , high temporal resolution may be critical for encoding dynamic stimuli as well as supporting rapid scene segmentation . in the case of saccades , the bias toward segregation
may also reflect the need of the visual system to preserve separate retinal images across saccades or may be a strategy to account for lingering effects of saccadic remapping [ 30 , 41 ] .
because eye movements are used to actively sample the environment , the close coordination between motor and sensory systems found here might compensate for the drastic sensory changes associated with each saccade and prepare the  visual system for a new spatiotemporal pattern of input with each new fixation ; for reviews , see [ 30 , 31 , 41 ] .
consistent with this idea , recent neurophysiological studies have demonstrated saccade - related phase resets of ongoing oscillations in the local field potential of temporal lobe regions during natural viewing [ 32 , 33 , 34 ] and , in particular , in theta frequencies around 35  hz [ 35 , 36 ] . here , we show that saccades reset fluctuations in human perceptual processing consistent with a dampened oscillation in the theta range ( 35  hz ) .
the alignment of processing to new fixations , either by resetting ongoing oscillations or by creating a new fluctuation ex novo , influenced processing for less than 1 s , possibly due to factors such as the intentions to make further saccades or micro - saccades ( resetting the fluctuation ) or neural oscillators moving out of phase .
for both meg and behavioral measures , integration performance became more dominant in the second phase .
integration supports the more extended processing of dynamic or complex stimuli   and may ensure the consolidation and stability of specific object representations over time and across saccades [ 11 , 12 , 18 , 30 ] .
however , integration requires temporal buffering of sensory input for extended processing , at the cost of temporal precision and local details .
thus , there is a natural trade - off between the needs for integration and segregation .
one potential explanation for the overall pattern of results found here is that perceptual outcome , in terms of whether two stimuli are integrated or segregated , may depend on a single oscillatory mechanism [ 16 , 22 , 43 , 44 , 45 ] .
for example , studies of trial - by - trial variability in seeing two flashes as either a single event or two events [ 16 , 45 ] , as well as studies of integration masking , have also shown that the ability to segregate two stimuli depends on the timing of those events with respect to the phase of oscillatory activity .
serial ,  bottom - up mechanism in which perception is determined by whether the two stimuli fall into the same , or different , cycles ; see also . such studies , which used variants of a temporal segregation task , rather than both integration and segregation , suggest that cortical oscillations provide natural temporal frames for the grouping or chunking of neural activity [ 43 , 44 ] . alternatively , sensory systems might perform integration and segregation , at least partially , in parallel , and the time course differences found here might , then , result from an active , top - down bias toward either state .
information initially used to segregate the two displays ( in the first phase ) may be maintained in a temporal buffer / window in order to also support temporal integration in the second phase , followed by segregation again in the third  phase .
previous trans - cranial magnetic stimulation ( tms ) studies have demonstrated such long - lasting biasing signals for feature integration in visual cortex .
in addition , evidence for retention of information across multiple oscillatory cycles comes from studies showing regularly recurring  perceptual echoes  at 10  hz   and integration cycles at 5  hz for repeated natural images . in conclusion ,
the present study provides converging evidence for behavioral and neural oscillations in states of neural susceptibility and suggests that these alternations may play a role not just in the detection of sub - threshold stimuli   but also , more generally , in the parsing of continuous sensory input . specifically , these findings link alternations in neural processing and perception to phase reset / alignment based on input transitions such as stimulus onsets or saccadic eye movements .
overall , these findings suggest that the alignment of integration windows to new sensory or oculomotor events may serve as an organizing principle for the temporal processing of continuous sensory input .
participants gave written , informed consent before each experimental session . in all experiments , participants viewed the same sequence of two patterns separated by a brief isi but were instructed to locate either the missing element ( which requires temporal integration ) or the odd element ( segregation ) in separate blocks ( figure  1a ) .
we used a blocked design based on pilot studies , which showed that participants were worse at performing both tasks simultaneously . in a random - trial design , participants typically chose the strategy of prioritizing one task over the other , with poor performance in the non - prioritized task .
thus , the blocked design with explicit task instructions ensured equal performance and physically identical stimuli in the two tasks ( both targets were shown on each trial , but only one was task relevant in each block ) . psychophysical performance was matched between integration and segregation tasks by selecting a critical isi for each participant ( see the psychophysics section in results ) . in experiment 1 ,
the two displays ( 10-ms duration each  + subject - specific isi ) were presented after a randomly jittered pre - stimulus time period ( 12 s ) and followed by a response screen after 500  ms .
meg was recorded continuously to contrast pre - stimulus oscillatory activity , the stimulus - evoked fields , frequency - specific phase coherence , and mvpa decoding between tasks . in experiment 2
, we timed stimulus presentation ( 10  ms for each display  + 50-ms isi ) relative to eye fixation onset and contrasted the fixation - aligned behavioral time courses ( 500  ms in expt 2a , and 1,000  ms in expt 2b ) between tasks . a complete description of the materials and methods can be found in the online supplemental experimental procedures .
; methodology , a.w . ; formal analysis , a.w . ; investigation , a.w . and e.m .
; visualization , a.w . ; funding acquisition , d.m . ; resources , m.g.v.k . and n.w .
 summarywhen processing dynamic input , the brain balances the opposing needs of temporal integration and sensitivity to change . 
 we hypothesized that the visual system might resolve this challenge by aligning integration windows to the onset of newly arriving sensory samples . in a series of experiments , 
 human participants observed the same sequence of two displays separated by a brief blank delay when performing either an integration or segregation task . 
 first , using magneto - encephalography ( meg ) , we found a shift in the stimulus - evoked time courses by a 150-ms time window between task signals . 
 after stimulus onset , multivariate pattern analysis ( mvpa ) decoding of task in occipital - parietal sources remained above chance for almost 1 s , and the task - decoding pattern interacted with task outcome . in the pre - stimulus period , 
 the oscillatory phase in the theta frequency band was informative about both task processing and behavioral outcome for each task separately , suggesting that the post - stimulus effects were caused by a theta - band phase shift . 
 second , when aligning stimulus presentation to the onset of eye fixations , there was a similar phase shift in behavioral performance according to task demands . in both meg and behavioral measures , 
 task processing was optimal first for segregation and then integration , with opposite phase in the theta frequency range ( 35  hz ) . 
 the best fit to neurophysiological and behavioral data was given by a dampened 3-hz oscillation from stimulus or eye fixation onset . 
 the alignment of temporal integration windows to input changes found here may serve to actively organize the temporal processing of continuous sensory input . 
Introduction
Results
Discussion
Experimental Procedures
Author Contributions