All in Good Time: Long-Lasting Postdictive Effects Reveal Discrete Perception
Authors: Michael H. Herzog, Leila Drissi-Daoudi, Adrien Doerig
Journal: Trends in Cognitive Sciences (2020)

Conscious perception seems to be a continuous stream of percepts. Is this true? Recent research sheds new light on this age-old debate.In long-lasting postdictive effects, later events can determine the perception of events that occurred several hundreds of milliseconds earlier.Long-lasting postdiction requires high capacity buffers, which store information unconsciously for substantial periods of time. This favors a two-stage model, in which continuous unconscious processing precedes discrete conscious percepts.Such a two-stage model solves the problems of both traditional continuous and discrete models. Is consciousness a continuous stream of percepts or is it discrete, occurring only at certain moments in time? This question has puzzled philosophers, psychologists, and neuroscientists for centuries. Both hypotheses have fallen repeatedly in and out of favor. Here, we review recent studies exploring long-lasting postdictive effects and show that the results favor a two-stage discrete model, in which substantial periods of continuous unconscious processing precede discrete conscious percepts. We propose that such a model marries the advantages of both continuous and discrete models and resolves centuries old debates about perception and consciousness. Is consciousness a continuous stream of percepts or is it discrete, occurring only at certain moments in time? This question has puzzled philosophers, psychologists, and neuroscientists for centuries. Both hypotheses have fallen repeatedly in and out of favor. Here, we review recent studies exploring long-lasting postdictive effects and show that the results favor a two-stage discrete model, in which substantial periods of continuous unconscious processing precede discrete conscious percepts. We propose that such a model marries the advantages of both continuous and discrete models and resolves centuries old debates about perception and consciousness. Intuitively, consciousness seems to be a continuous stream of percepts. Imagine a diver jumping from a cliff down into the ocean. We feel that we see their motion trajectory at each moment of time. For this reason, most philosophical models propose that consciousness is continuous [1.Dainton B. Temporal consciousness.in: Zalta E.N. The Stanford Encyclopedia of Philosophy Winter 2018. Metaphysics Research Lab, Stanford University, 2018Google Scholar] (Box 1). However, despite their intuitive appeal, continuous theories of consciousness face a number of problems [2.Doerig A. et al.Building perception block by block: a response to Fekete et al..Neurosci. Conscious. 2019; (Published online January 28, 2019. https://doi.org/10.1093/nc/niy012)Crossref PubMed Scopus (10) Google Scholar, 3.Herzog M.H. et al.Time slices: what is the duration of a percept?.PLoS Biol. 2016; 14e1002433Crossref PubMed Scopus (90) Google Scholar, 4.VanRullen R. Koch C. Is perception discrete or continuous?.Trends Cogn. Sci. 2003; 7: 207-213Abstract Full Text Full Text PDF PubMed Scopus (421) Google Scholar]. In particular, sensory information must be integrated over time before motion, melodies, etc. can be perceived. Hence, consciousness cannot happen instantly.Box 1Philosophical ModelsMore than 1500 years ago, Saint Augustine was driven to despair [98.Augustine S. Les confessions de Saint Augustin. Charpentier, Libraire-Editeur, 1841Google Scholar]. Since only an infinitesimally short presence exists, he thought we can only be conscious at this infinitesimally short moment in time. But how can we then perceive motion and change, since both encompass past and future events? Augustine proposed that the past aspects come from memory (such models are called cinematic models). However, humans perceive motion directly, not through memory. For this reason, subsequent philosophers [99.Husserl E. The Phenomenology of internal time-consciousness. Marinus Hijhoff, The Hague1928/1964Google Scholar] proposed that infinitesimally short percepts contain past and future aspects (such models are called retentional models). Retentional models code temporal information in a nontemporal format, similar to how the color red is not coded by a red neuron. For example, sliding windows, in which information is constantly combined over the past few milliseconds, are one way to implement continuous retentional models (Box 2). More recent models propose that percepts are not infinitesimally short. They rather last for substantial amounts of time; that is, conscious moments are extended (such models are called extensional models). During these conscious periods, we directly perceive motion, for example.In accordance with intuition, consciousness is seen as a continuous stream in most classic philosophical models (continuous consciousness; left column). In psychology, research has focused less on how long a conscious percept lasts. Rather it has asked whether we are conscious at all times (right column) or only at certain discrete moments of time (left column). Many postdictive effects, known since ancient Buddhist times, favor discrete theories of consciousness. Combining the philosophical and psychological research directions, we arrive at six types of models (Figure I). Our two-stage model is a discrete retentional model (Figure I, middle-right panel). The classification of the philosophical models follows [1.Dainton B. Temporal consciousness.in: Zalta E.N. The Stanford Encyclopedia of Philosophy Winter 2018. Metaphysics Research Lab, Stanford University, 2018Google Scholar] (see [51.Lee G. Temporal experience and the temporal structure of experience.Philos. Impr. 2014; 14: 1-21Google Scholar,100.Miller J. Discrete and continuous models of human information processing: Theoretical distinctions and empirical results.Acta Psychol. 1988; 67: 191-257Crossref PubMed Scopus (232) Google Scholar] for other classifications). More than 1500 years ago, Saint Augustine was driven to despair [98.Augustine S. Les confessions de Saint Augustin. Charpentier, Libraire-Editeur, 1841Google Scholar]. Since only an infinitesimally short presence exists, he thought we can only be conscious at this infinitesimally short moment in time. But how can we then perceive motion and change, since both encompass past and future events? Augustine proposed that the past aspects come from memory (such models are called cinematic models). However, humans perceive motion directly, not through memory. For this reason, subsequent philosophers [99.Husserl E. The Phenomenology of internal time-consciousness. Marinus Hijhoff, The Hague1928/1964Google Scholar] proposed that infinitesimally short percepts contain past and future aspects (such models are called retentional models). Retentional models code temporal information in a nontemporal format, similar to how the color red is not coded by a red neuron. For example, sliding windows, in which information is constantly combined over the past few milliseconds, are one way to implement continuous retentional models (Box 2). More recent models propose that percepts are not infinitesimally short. They rather last for substantial amounts of time; that is, conscious moments are extended (such models are called extensional models). During these conscious periods, we directly perceive motion, for example. In accordance with intuition, consciousness is seen as a continuous stream in most classic philosophical models (continuous consciousness; left column). In psychology, research has focused less on how long a conscious percept lasts. Rather it has asked whether we are conscious at all times (right column) or only at certain discrete moments of time (left column). Many postdictive effects, known since ancient Buddhist times, favor discrete theories of consciousness. Combining the philosophical and psychological research directions, we arrive at six types of models (Figure I). Our two-stage model is a discrete retentional model (Figure I, middle-right panel). The classification of the philosophical models follows [1.Dainton B. Temporal consciousness.in: Zalta E.N. The Stanford Encyclopedia of Philosophy Winter 2018. Metaphysics Research Lab, Stanford University, 2018Google Scholar] (see [51.Lee G. Temporal experience and the temporal structure of experience.Philos. Impr. 2014; 14: 1-21Google Scholar,100.Miller J. Discrete and continuous models of human information processing: Theoretical distinctions and empirical results.Acta Psychol. 1988; 67: 191-257Crossref PubMed Scopus (232) Google Scholar] for other classifications). For this reason, discrete theories of consciousness, in which conscious percepts occur only at certain moments of time, have been proposed (Box 1). Traditionally, the duration of a discrete percept is determined by the temporal resolution of conscious perception (see Glossary) [4.VanRullen R. Koch C. Is perception discrete or continuous?.Trends Cogn. Sci. 2003; 7: 207-213Abstract Full Text Full Text PDF PubMed Scopus (421) Google Scholar, 5.Pöppel E. A hierarchical model of temporal perception.Trends Cogn. Sci. 1997; 1: 56-61Abstract Full Text PDF PubMed Scopus (479) Google Scholar, 6.Pöppel E. Pre-semantically defined temporal windows for cognitive processing.Philos. Trans. R. Soc. Lond. B Biol. Sci. 2009; 364: 1887-1896Crossref PubMed Scopus (138) Google Scholar, 7.Allport D.A. Phenomenal simultaneity and the perceptual moment hypothesis.Br. J. Psychol. 1968; 59: 395-406Crossref PubMed Scopus (140) Google Scholar]. For example, two lines are perceived as simultaneous even when presented with a delay of 40 ms [8.Kristofferson A.B. Attention and psychophysical time.Acta Psychol. 1967; 27: 93-100Crossref PubMed Scopus (85) Google Scholar, 9.Elliott M.A. et al.The effects of subthreshold synchrony on the perception of simultaneity.Psychol. Res. 2007; 71: 687-693Crossref PubMed Scopus (23) Google Scholar, 10.White P.A. Is conscious perception a series of discrete temporal frames?.Conscious. Cogn. 2018; 60: 98-126Crossref PubMed Scopus (36) Google Scholar]. For longer delays the nonsimultaneity is detected. Thus, it may seem that a discrete percept is about 40 ms long. However, the temporal resolution of conscious perception depends strongly on the stimulus paradigm and parameters, extending over two orders of magnitude from 3 ms (apparent motion; [11.Westheimer G. McKee S.P. Perception of temporal order in adjacent visual stimuli.Vis. Res. 1977; 17: 887-892Crossref PubMed Scopus (77) Google Scholar]) to over 100 ms (color change during motion; [12.Holcombe A.O. Seeing slow and seeing fast: two limits on perception.Trends Cogn. Sci. 2009; 13: 216-221Abstract Full Text Full Text PDF PubMed Scopus (155) Google Scholar,13.Moutoussis K. Zeki S. A direct demonstration of perceptual asynchrony in vision.Philos. Trans. R. Soc. Lond. B Biol. Sci. 1997; 264: 393-399Google Scholar]). Hence, it seems there is no universal duration for discrete percepts, challenging discrete theories in general [3.Herzog M.H. et al.Time slices: what is the duration of a percept?.PLoS Biol. 2016; 14e1002433Crossref PubMed Scopus (90) Google Scholar,10.White P.A. Is conscious perception a series of discrete temporal frames?.Conscious. Cogn. 2018; 60: 98-126Crossref PubMed Scopus (36) Google Scholar]. We call this the problem of multiple temporal resolutions [3.Herzog M.H. et al.Time slices: what is the duration of a percept?.PLoS Biol. 2016; 14e1002433Crossref PubMed Scopus (90) Google Scholar,10.White P.A. Is conscious perception a series of discrete temporal frames?.Conscious. Cogn. 2018; 60: 98-126Crossref PubMed Scopus (36) Google Scholar]. Much discussion about the temporal aspects of consciousness centers on effects shorter than 100 ms and whether or not low level mechanisms, such as visual persistence or short neural latencies (<100 ms), support discrete or continuous perception [6.Pöppel E. Pre-semantically defined temporal windows for cognitive processing.Philos. Trans. R. Soc. Lond. B Biol. Sci. 2009; 364: 1887-1896Crossref PubMed Scopus (138) Google Scholar,14.Breitmeyer B. Öğmen H. Visual Masking: Time Slices through Conscious and Unconscious Vision. Oxford University Press, 2006Crossref Scopus (387) Google Scholar, 15.Efron R. The duration of the present.Ann. N. Y. Acad. Sci. 1967; 138: 713-729Crossref Scopus (108) Google Scholar, 16.Holcombe A. The temporal organization of perception.in: Wagemans J. Handbook of Perceptual Organization. Oxford University Press, 2013: 820-840Google Scholar, 17.Montemayor C. Wittmann M. The varieties of presence: hierarchical levels of temporal integration.Timing Time Percept. 2014; 2: 325-338Crossref Google Scholar]. Recently, long-lasting postdictive effects have brought the debate in a territory beyond the reach of low level mechanisms, provoking a rethinking about the temporal structure of consciousness [2.Doerig A. et al.Building perception block by block: a response to Fekete et al..Neurosci. Conscious. 2019; (Published online January 28, 2019. https://doi.org/10.1093/nc/niy012)Crossref PubMed Scopus (10) Google Scholar,3.Herzog M.H. et al.Time slices: what is the duration of a percept?.PLoS Biol. 2016; 14e1002433Crossref PubMed Scopus (90) Google Scholar,10.White P.A. Is conscious perception a series of discrete temporal frames?.Conscious. Cogn. 2018; 60: 98-126Crossref PubMed Scopus (36) Google Scholar,18.VanRullen R. Perceptual cycles.Trends Cogn. Sci. 2016; 20: 723-735Abstract Full Text Full Text PDF PubMed Scopus (308) Google Scholar, 19.White P.A. The three-second "subjective present": a critical review and a new proposal.Psychol. Bull. 2017; 143: 735Crossref PubMed Scopus (24) Google Scholar, 20.Fekete T. et al.In the interest of saving time: a critique of discrete perception.Neurosci. Conscious. 2018; (Published online April 19, 2018. https://doi.org/10.1093/nc/niy003)Crossref PubMed Google Scholar]. Here, we argue that the temporal structure of consciousness cannot be determined by investigating the temporal parameters of the content of consciousness, but postdictive effects can provide upper and lower bounds. We review the literature and propose a two-stage model, in which long-lasting unconscious processing precedes discrete conscious percepts. We explain how such a model marries the advantages of both traditional continuous and discrete models. Finally, we outline important implications for neuroscience, consciousness, and philosophy. Investigating whether conscious perception is continuous or discrete is challenging. We can measure the subjective duration of the content of consciousness; for example, the perceived duration of a stimulus. However, it is an open question whether we can measure how long a percept itself lasts. As mentioned, the temporal resolution of the content of conscious perception is often used to determine the duration of a percept. However, the temporal resolution of conscious perception and the temporal structure of consciousness (i.e., whether it is continuous or discrete, how often discrete percepts occur, etc.) are logically independent. For example, if nonsimultaneity detection has a temporal resolution of 40 ms, this only tells us about the temporal resolution of the nonsimultaneity detector, which may operate fully unconsciously. It does not show that conscious percepts themselves last 40 ms, nor that consciousness is discrete or continuous. Nevertheless, as we show, postdictive effects can provide temporal bounds on conscious perception. In postdictive effects, a late stimulus can affect perception of another stimulus presented earlier, which differs from priming, where earlier stimuli affect perception of later ones. In certain postdictive effects, earlier and later stimuli can even mutually affect each other and bring about truly integrated percepts. For example, in color fusion, a red disk is presented for 40 ms, followed by a 40-ms green disk at the same location. The percept is a single yellow disk [21.Efron R. Conservation of temporal information by perceptual systems.Percept. Psychophys. 1973; 14: 518-530Crossref Scopus (60) Google Scholar,22.Pilz K.S. et al.Long-lasting visual integration of form, motion, and color as revealed by visual masking.J. Vis. 2013; 1312–12Crossref Scopus (11) Google Scholar]. There is no red or green in the percept. Hence, the representations of the red and green disks influence each other and form a single percept. The percept cannot have occurred before 80 ms; that is, before the second disk appeared. Hence, with postdictive effects we can empirically investigate how long unconscious processing lasts before a conscious percept occurs. In the SQM paradigm [23.Otto T.U. et al.The flight path of the phoenix – the visible trace of invisible elements in human vision.J. Vis. 2006; 6: 1079-1086Crossref PubMed Scopus (61) Google Scholar,24.Otto T.U. et al.Feature integration across space, time, and orientation.J. Exp. Psychol. Hum. Percept. Perform. 2009; 35: 1670-1686Crossref PubMed Scopus (25) Google Scholar] (Figure 1), a sequence of vertical lines is presented, eliciting the percept of two diverging motion streams. When one of the lines has a horizontal vernier offset, all other lines are perceived as offset in the same direction – even though they are in fact straight. Observers can easily report the perceived vernier offset (left vs right) but they cannot locate which specific line carries the offset [23.Otto T.U. et al.The flight path of the phoenix – the visible trace of invisible elements in human vision.J. Vis. 2006; 6: 1079-1086Crossref PubMed Scopus (61) Google Scholar]. When several verniers are present in the stream, the offsets integrate (Figure 1). This integration is spatiotemporally precise. For example, only offsets within a motion stream integrate; that is, they segregate if they are in different streams [23.Otto T.U. et al.The flight path of the phoenix – the visible trace of invisible elements in human vision.J. Vis. 2006; 6: 1079-1086Crossref PubMed Scopus (61) Google Scholar]. Most importantly, integration is mandatory. Even when observers are told that there are two verniers in the SQM stream, they are unable to report the two offsets separately (Figure 1; [25.Drissi-Daoudi L. et al.Feature integration within discrete time windows.Nat. Commun. 2019; 10: 1-8Crossref PubMed Scopus (19) Google Scholar]). They perceive only one single integrated offset; that is, they have no conscious access to the individual offsets. This mandatory and mutual integration lasts up to 450 ms, depending on the observer. If the verniers are 490 ms apart, their offsets are perceived separately and can be reported individually (Figure 1; [25.Drissi-Daoudi L. et al.Feature integration within discrete time windows.Nat. Commun. 2019; 10: 1-8Crossref PubMed Scopus (19) Google Scholar]). Hence, there is a long unconscious processing period before a conscious percept occurs with a lower bound of ~400 ms and an upper bound of 490 ms. Furthermore, these unconscious processing windows seem to be temporally discrete. When three offsets are presented in the stream (at 0, 330, and 490 ms), only the first two integrate. The third vernier is reported independently, even though it is temporally twice as close to the second than to the first vernier (160 vs 330 ms). It seems that vernier offsets integrate only when they are in the same discrete window lasting ~400 ms. Similar long-lasting postdictive effects have been reported in a variety of other visual paradigms. For example, in a rapid serial visual presentation (RSVP) task, integration times up to 240 ms have been reported [26.Akyürek E.G. Wolff M.J. Extended temporal integration in rapid serial visual presentation: Attentional control at Lag 1 and beyond.Acta Psychol. 2016; 168: 50-64Crossref PubMed Scopus (16) Google Scholar]. As another example, a cue presented up to 400 ms after a faint Gabor grating can influence whether or not the grating is consciously perceived (Figure 2A ; [27.Sergent C. et al.Cueing attention after the stimulus is gone can retrospectively trigger conscious perception.Curr. Biol. 2013; 23: 150-155Abstract Full Text Full Text PDF PubMed Scopus (92) Google Scholar, 28.Sergent C. The offline stream of conscious representations.Philos. Trans. R. Soc. Lond. B Biol. Sci. 2018; 373: 20170349Crossref PubMed Scopus (18) Google Scholar, 29.Thibault L. et al.Retrospective attention gates discrete conscious access to past sensory stimuli.PLoS One. 2016; 11e0148504Crossref PubMed Scopus (26) Google Scholar, 30.Xia Y. et al.Retrospective triggering of conscious perception by an interstimulus interaction.J. Vis. 2016; 163–3Crossref Scopus (8) Google Scholar]). Finally, volition can affect the perception of stimuli presented 300 ms earlier [31.Sun L. et al.Back from the future: volitional postdiction of perceived apparent motion direction.Vis. Res. 2017; 140: 133-139Crossref PubMed Scopus (5) Google Scholar]. Long-lasting postdictive effects are not restricted to vision but also occur in audition [32.McWalter R. McDermott J.H. Illusory sound texture reveals multi-second statistical completion in auditory scene analysis.Nat. Commun. 2019; 10: 1-18Crossref PubMed Scopus (13) Google Scholar] and across modalities [33.Sergent C. et al.Top-down modulation of human early visual cortex after stimulus offset supports successful postcued report.J. Cogn. Neurosci. 2011; 23: 1921-1934Crossref PubMed Scopus (28) Google Scholar,34.Rimsky-Robert D. et al.Retrospective auditory cues can improve detection of near-threshold visual targets.Sci. Rep. 2019; 9: 1-11Crossref PubMed Scopus (3) Google Scholar]. For example, three flashes were presented, each paired with a sound. When the central flash was missing but the central sound was present, a central flash was illusorily perceived. When the central flash was present but the central sound was absent, the central flash was illusorily perceived as absent ([35.Stiles N.R.B. et al.What you saw is what you will hear: two new illusions with audiovisual postdictive effects.PLoS One. 2018; 13e0204217Crossref PubMed Scopus (9) Google Scholar]; Figure 2B). Hence, motion can be disambiguated and elements can be illusorily suppressed or added postdictively across hundreds of milliseconds. In most of the above examples, postdiction occurred with stimuli presented several hundreds of milliseconds apart. Many postdictive effects are shorter than 100 ms [36.Sugita Y. et al.Visual percepts modify iconic memory in humans.Sci. Rep. 2018; 8: 1-7Crossref PubMed Scopus (8) Google Scholar, 37.Schouten J.F. Subjective stroboscopy and a model of visual movement detectors.in: Models for the Perception of Speech and Visual Form: Proceedings of a Symposium. MIT Press, 1967: 44-55Google Scholar, 38.Purves D. et al.The wagon wheel illusion in movies and reality.Proc. Natl. Acad. Sci. 1996; 93: 3693-3697Crossref PubMed Scopus (111) Google Scholar, 39.Shimojo S. Postdiction: its implications on visual awareness, hindsight, and sense of agency.Front. Psychol. 2014; 5: 196Crossref PubMed Scopus (55) Google Scholar, 40.Eagleman D.M. Sejnowski T.J. Motion integration and postdiction in visual awareness.Science. 2000; 287: 2036-2038Crossref PubMed Scopus (397) Google Scholar]. For example in visual masking, masks presented about 100 ms after the target do not interfere with the target anymore [14.Breitmeyer B. Öğmen H. Visual Masking: Time Slices through Conscious and Unconscious Vision. Oxford University Press, 2006Crossref Scopus (387) Google Scholar]. Still, even when postdictive effects are short, conscious percepts may occur later, emphasizing again that temporal resolution and temporal structure of consciousness are independent. For instance, it was shown that target visibility in masking can be decoded from brain imaging data only >250 ms after stimulus onset, even though the stimulus itself is shorter (Figure 2C; [41.Del Cul A. et al.Brain dynamics underlying the nonlinear threshold for access to consciousness.PLoS Biol. 2007; 5e260Crossref PubMed Scopus (511) Google Scholar,42.King J.-R. et al.Brain mechanisms underlying the brief maintenance of seen and unseen sensory information.Neuron. 2016; 92: 1122-1134Abstract Full Text Full Text PDF PubMed Scopus (98) Google Scholar]). Similarly, in RSVP tasks, multiple images can unconsciously cohabit for hundreds of milliseconds, but only the ones that are available for conscious report elicit late activity around 350 ms [43.Marti S. Dehaene S. Discrete and continuous mechanisms of temporal selection in rapid visual streams.Nat. Commun. 2017; 8: 1-13Crossref PubMed Scopus (50) Google Scholar]. Relatedly, crossmodal integration of audiovisual stimuli presented for 120 ms can take more than 200 ms [44.Fiebelkorn I.C. et al.Staying within the lines: the formation of visuospatial boundaries influences multisensory feature integration.Eur. J. Neurosci. 2010; 31: 1737-1743Crossref PubMed Scopus (23) Google Scholar]. Even though it is unclear which electroencephalography event-related potentials (e.g., VAN around 200 ms or P300 around 400 ms) are linked to consciousness [45.Koivisto M. Revonsuo A. Event-related brain potential correlates of visual awareness.Neurosci. Biobehav. Rev. 2010; 34: 922-934Crossref PubMed Scopus (178) Google Scholar], these results suggest that conscious percepts may take hundreds of milliseconds to form. Percepts can be altered by transcranial magnetic stimulation (TMS) during a long-lasting period after the stimulus is gone [46.Scharnowski F. et al.Long-lasting modulation of feature integration by transcranial magnetic stimulation.J. Vis. 2009; 91–1Crossref Scopus (35) Google Scholar]. Two vernier offsets are presented in succession for 30 ms each. The two verniers fuse [21.Efron R. Conservation of temporal information by perceptual systems.Percept. Psychophys. 1973; 14: 518-530Crossref Scopus (60) Google Scholar,22.Pilz K.S. et al.Long-lasting visual integration of form, motion, and color as revealed by visual masking.J. Vis. 2013; 1312–12Crossref Scopus (11) Google Scholar]; that is, the resulting percept is a single aligned vernier, similarly to the color fusion example mentioned before. TMS modulates the perceived offset up to 370 ms: for early TMS pulses, the fused vernier is predominantly perceived to have an offset in the direction of the second vernier, while the first vernier dominates the percept for later TMS pulses. Hence, the two verniers must have independent unconscious representations for as long as 370 ms. Therefore, even for short stimulus durations, there seems to be a long-lasting window during which the percept can be modified postdictively. As shown, elements can postdictively interact with each other across hundreds of milliseconds before a conscious percept emerges. Elements can integrate or segregate, be added or suppressed, fused, disambiguated and potentially there is more. The SQM suggests that these postdictive effects occur in discrete temporal windows. How can these long-lasting and complex effects be explained? Classically, interactions between temporally distinct stimuli are discussed in terms of low-level neural processing, such as visual persistence [47.Eriksen C.W. Collins J.F. Some temporal characteristics of visual pattern perception.J. Exp. Psychol. 1967; 74: 476Crossref PubMed Scopus (195) Google Scholar] or short neural latency differences [16.Holcombe A. The temporal organization of perception.in: Wagemans J. Handbook of Perceptual Organization. Oxford University Press, 2013: 820-840Google Scholar], which are typically assumed to happen before 100 ms [48.Lamme V.A. Roelfsema P.R. The distinct modes of vision offered by feedforward and recurrent processing.Trends Neurosci. 2000; 23: 571-579Abstract Full Text Full Text PDF PubMed Scopus (1583) Google Scholar, 49.Foxe J.J. Simpson G.V. Flow of activation from V1 to frontal cortex in humans.Exp. Brain Res. 2002; 142: 139-150Crossref PubMed Scopus (523) Google Scholar, 50.Center E.G. et al.Examining the role of feedback in TMS-induced visual suppression: a cautionary tale.Conscious. Cogn. 2019; 75: 102805Crossref PubMed Scopus (4) Google Scholar]. For example, masking may be explained by proposing that the mask catches up with the target because the mask is processed with a shorter latency. However, the long-lasting postdictive effects we review operate on a longer timescale and are too specific for such explanations. There are two avenues of explanation: discrete models and delayed continuous models. In continuous models, even though consciousness of a stimulus is substantially delayed, there is always a conscious percept. Continuous models may explain long-lasting postdiction by sliding windows: elements are combined over the past few hundreds of milliseconds and the output is continuously delivered as a conscious percept [20.Fekete T. et al.In the interest of saving time: a critique of discrete perception.Neurosci. Conscious. 2018; (Published online April 19, 2018. https://doi.org/10.1093/nc/niy003)Crossref PubMed Google Scholar,51.Lee G. Temporal experience and the temporal structure of experience.Philos. Impr. 2014; 14: 1-21Google Scholar] (R. Grush, unpublished). However, this would create too many percepts (we call this the too-many-percepts problem; Box 2; [1.Dainton B. Temporal consciousness.in: Zalta E.N. The Stanford Encyclopedia of Philosophy Winter 2018. Metaphysics Research Lab, Stanford University, 2018Google Scholar,2.Doerig A. et al.Building perception block by block: a response to Fekete et al..Neurosci. Conscious. 2019; (Published online January 28, 2019. https://doi.org/10.1093/nc/niy012)Crossref PubMed Scopus (10) Google Scholar], R. Grush, unpublished). For example, in the SQM, the window would first contain large parts of the empty pre-SQM screen and the first vernier offset. Observers perceive only this offset. When the window p